Explanation:

Hospital acquired pneumonia (or nosocomial pneumonia) is defined as a pneumonia that mates more than 48 hours after admission to the hospital. It more commonly affects patients who are in the ICU or are mechanically ventilated. The most frequent causative microorganisms are Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumoniae, E.coli, and Enterobacter. Pathologic features are those of acute bronchopneumonia, but the mortality rate is high, around 50%. Anaerobic pneumonia occurs in individuals predisposed to aspiration, i.e., those with depressed levels of consciousness, impaired deglutition, or tracheal/nasogastric tubes. Periodontal disease is an additional risk factor, as it leads to increased numbers of anaerobic bacteria in aspirated material. Necrotizing pneumonia, lung abscess, and pleural empyema are the most common pathologic lesions. Community acquired pneumonia is usually caused by pneumococcus (Streptococcus pneumoniae) and results in homogeneous consolidation of an entire lobe. Microscopically, a fibrinopurulent exudate fills the alveolar spaces. Lipid pneumonia is characterized histologically by large numbers of lipid-laden macrophages. This form of pneumonia occurs in association with obstructive bronchial lesions or aspiration of mineral oils. In primary atypical pneumonia there is a lympho monocytic infiltrate confined to interalveolar septa and interstitium. Mycoplasma pneumoniae is the most frequent etiologic agent.

Explanation:

Adults with sickle cell disease have undergone decades of accelerated RBC formation and destruction, leading to accelerated erythropoiesis in the bone marrow. Consequently, the bone marrow becomes hyperplastic, with marked increases in the number of normoblasts (erythroblasts) at the expense of marrow fat and marrow bone. Although the white cell and megakaryocyte lines are undiminished, there is a marked increase in RBC precursors and iron stores. Iron storage increases as a consequence of both chronic transfusions and increased dietary absorption; these increased iron stores can be appreciated with a Prussian blue stain.

Explanation:

The most common cause of thrombocytosis is a reactive thrombocytosis. Thrombocythaemia may occur in any of the myeloproliferative disorder particularly polycythaemia rubra vera (PRV). Thrombopoietin is the key hormone in the regulation of megakaryocyte differentiation. Secondary thrombocytosis does not place the patient at risk for haemostatic or cardiovascular events.

Explanation:

Chlamydia psittaci is endemic in birds including psittacine birds, canaries, finches, pigeons and poultry. Pet owners, vets and zoo keepers are most at risk. It is rare in children. Person to person transmission occurs especially in a hospital environment. Sputum Gram stain reveals a few leucocytes and no predominant bacteria. There are few signs and few laboratory/x ray findings. Positive serology is with complement fixing antibodies. It is treated with tetracycline.

Explanation:

Klinefelter´s syndrome and Down syndrome are diagnosed principally by chromosomal analysis/karyotype – XXY in the former and trisomy 21 or translocation in the latter. A trinucleotide CAG repeat expansion in the Huntington gene is diagnostic of Huntington disease.
The majority of cases of hypertrophic cardiomyopathy (HOCM) are autosomal dominantly inherited yet defective genes are located on a variety of chromosomes.
DNA linkage analysis is used to assist in the diagnosis of adult polycystic kidney disease (PCKD) but the presence of multiple copies continues to complicate the development of reagents for direct genetic testing, at least of the 70% of PKD1 that is replicated elsewhere.

Explanation:

α1-antitrypsin deficiency is inherited in an autosomal recessive pattern, which causes emphysema and cirrhosis and has a prevalence of 1 in 2500

Explanation:

Type I hypersensitivity, also known as immediate or anaphylactic hypersensitivity, usually takes 15 – 30 minutes from the time of exposure to the antigen. The reaction may cause a range of symptoms from minor inconvenience to death. The reaction involves preferential production of IgE, in response to certain antigens, which in turn initiates a sequence of event: leading to the release various pharmacologically active substances that are responsible for the clinical features. Diagnostic tests include skin tests, measurement of total IgE and specific IgE antibodies against the suspected allergens. However, this question asks which of the following tests would provide confirmatory information and that would be Tryptase. Tryptase is a neutral protease stored in mast cell secretory granules that is secreted by human mast cells. Levels in normal blood are undetectable (< l ng/ml). Elevated serum levels demonstrate that mast cell activation with mediator release has occurred whether triggered IgE-mediated anaphylaxis or non-IgE-mediated anaphylactoid reactions. The greater the severity of anaphylaxis, the more likely that serum -tryptase levels will be elevated

Explanation:

When requesting an ANCA test, both immunofluorescence and an ELISA test are generally performed. On immunofluoresecence, if ANCA are present the staining pattern; the staining pattern may be cytoplasmic (cANCA) or perinuclear (pANCA). Typical antigen specificity includes proteinase 3 or myeloperoxidase. cANCA and specificity for the PR-3 antigen is most specific for Wegener´s granulomatosis. This pattern is also seen in microscopic polyarteritis nodosa and rarely Churg-Strauss syndrome. PANCA and MPO are less specific findings detected in various vasculitic illnesses and occasionally in chronic infections.

Explanation:

Adipocytes cease growth after they reach a volume of approximately one microgram (C). Adipocytes (fat cells) form a reservoir of energy that expands or contracts, depending on the energy balance of the organism (A). These cells develop from precursor preadipocytes to accommodate excess nutrient calories (B). New adipocytes are formed ad infinitum in response to continuing positive energy balance (D). Despite subsequent weight loss, the fat cell number remains constant (E).

Explanation:

CA-125 may be elevated in ovarian epithelial tumors, such as a cystadenocarcinoma. AFP can be elevated with either an endodermal sinus tumor or embryonal carcinoma. An elevated hCG can be seen with choriocarcinomas. Sertoli-Leydig and granulosa-theca cell tumors do not usually produce an elevated CA- 125, AFP, or hCG level;

Explanation:

Decreased size of the female reproductive organs and breasts is a direct consequence of estrogen deficiency. Menopause is defined as the final episode of menstrual bleeding in women. The climacteric is the physiologic period during which ovarian function regresses. The menstrual cycle shortens due to a shortened follicular phase, with increased FSH, normal LH, and decreased E2 and progesterone, when compared to normal ovulatory cycles. Vasomotor instability typified by the hot flash, is accompanied by decreased skin resistance, peripheral vasodilatation, and LH pulses. Development of osteoporosis is affected by many factors, including diet, smoking, and estrogen deprivation.

Explanation:

As currently understood, a series of genetic changes occur in concert to initially produce an adenoma that may subsequently progress to a carcinoma. The initial step probably involves a mutation of the K-ras proto-oncogene. The gene for familial adenomatous polyposis has been mapped to chromosome 5. Chromosome 17(p53 gene) and chromosome 18 (DDC gene) deletions are thought to be important in malignant transformation. Overexpression of the c-myc gene has been reported in colon cancers.

Explanation:

Although 70% of compound fractures are contaminated with bacteria, less than 10% result in infection because of extensive operative debridement and perioperative antibiotic therapy. The anatomic location of hematogenous osteomyelitis depends on the age of the affected person. In children, hematogenous osteomyelitis usually affects the metaphysis of the long bones due to its large blood flow. In adults, the vertebrae are more vascular than other skeletal tissues. Therefore, bacteremias seed vertebral bodies preferentially at the more vascular anterior end plates. In up to two thirds of diabetics, osteomyelitis may develop by contiguous spread from an infected foot ulcer. Indwelling foreign bodies, such as prosthetic joints, decrease the quantity of bacteria necessary to establish a bone infection. These devices also permit pathogens to persist on their surface, protected from circulating immune factors and systemic antibiotics.

Explanation:

Macrophages are long lived phagocytic cells important in the inflammatory response. Some of the many secretory products of macrophages include binding proteins such as fibronectin, enzyme inhibitors such as alpha-2 macroglobulins, pyrogens such as interleukin I, and tumor necrosis factor, also known as cachectin. Exotoxin is secreted by bacteria

Explanation:

Surface components and extracellular products produced by Group A streptococci are important in the development of infection. The M protein is the major surface protein of Group A streptococci. This protein acts as a membrane anchor and correlates with the capacity of a strain to resist phagocytic killing. The extracellular enzyme, hyaluronidase, facilitates the spread of infection along fascial planes by hydrolyzing hyaluronic acid in deeper tissues. Pyrogenic exotoxins types A, B, and C induce lymphocyte blastogenesis, potentiate endotoxin-induced shock, induce fever, and suppress antibody synthesis. Streptolysins O and S damage cell membranes and account for the hemolysis produced by the bacterium. CAMP factor is a phospholipase produced by Group B streptococci, which causes hemolysis synergistically with beta-lysins.

Explanation:

Wegener´s granulomatosis is an immune disorder associated with abnormal production of c-ANCA autoantibodies. The vasculitis typically affects small and medium sized vessels. However, there is often an accompanying necrotizing glomerulonephritis and necrotizing granuloma formation in the upper respiratory tract. The therapy for Wegener´s granulomatosis is immunosuppression. “Palpable purpura” is associated with hypersensitivity angiitis.

Explanation:

A single dose of a prophylactic antibiotic given as surge is about to begin (sometimes given intravenously to assure the timing) has become more common because it is associated with a decreased wound infection rate. Such antibiotic usage does not prevent organisms from entering the tissues, but effectively prevents them from becoming established as they try to grow and divide (e.g., leave the lag phase and enter the log or exponential phase of colony growth). The stationary phase and phase of decline (formerly called death phase) would occur much later, after a colony had been established (which is what the surgeons were trying to prevent).

Explanation:

The ABO blood group allotypes reflect the presence of glycoproteins on the erythrocyte surface. Humans make IgM isohemagglutinins naturally against similar glycoproteins found on the surface of normal flora organisms, but self-tolerance should prevent the production of antibodies that would agglutinate the person´s own erythrocytes. This patient is AB, Rh+. Persons with this blood type will not possess isohemagglutinins in their bloodstream against either A or B antigens. Their PBCO will agglutinate in the presence of sera from individuals with type A, type B or type C blood. The Rh factor is either present (+) or absent (-) from red cells. Since the patient´s cells agglutinated in the presence of anti-Rh serum, it is clear that the patient is ´RhD+.
In emergencies, it is always a convenient short cut to use blood that is C, RhD-, the “universal donor,” since it has none of the alloantigens that could be recognized on the surfaces of cells. The question, however, inquires which type of blood would match the patient, not which could be used in case of emergency.

Explanation:

Severe combined immunodeficiency (SCID) is associated with deficiencies in both Band T cells due to a defect in differentiation of an early stem cell. Over 50 % of the cases are caused by a gene defect on the X chromosome, resulting in a defective IL-2 receptor. Adenosine deaminase deficiency is an autosomal recessive disease characterized by a deficiency of adenosine deaminase, which results in accumulation of metabolites that are toxic to both B and T stem cells in the bone marrow. Children with severe infections usually die within the first 2 years of life unless they receive bone-marrow transplants. A defective CD40L molecule causes hyper-IgM syndrome. This makes it impossible for B lymphocytes to receive the signal to switch isotypes, and they are therefore “stuck” making IgM alone. It is not classified as a SCID. Inability to produce MHC-II causes bare lymphocyte syndrome, which causes patients to be unable to produce CD4 cells. It results in a type of SCID since TH cells are necessary for the function of all immune responses. Nonsense mutation of rag genes results in a SCID because without the ability to perform VDJ recombinations, lymphocytes cannot express surface receptors for antigen; and in that case, lymphocyte precursors are induced to undergo apoptosis in the bone marrow. Recombination activating genes (rag genes) are responsible for the VDJ rearrangements that allow lymphocytes to create the idiotype of their antigen receptors.

Explanation:

Common variable immunodeficiency is a disease caused by abnormal B cell differentiation, characterized by decreased numbers of plasma cells and inadequate immunoglobulin production of all classes. It is distinguished from Bruton X-linked hypogammaglobulinemia by the fact that the number of B lymphocytes in the blood and lymphoid organs will be near normal. In Bruton agammaglobulinemia, B-cell maturation stops after the rearrangement of heavy-chain genes, and therefore, B cells in the bloodstream and lymphoid organs will be decreased in number or absent. Absence of plasma cells would be expected with both common variable immunodeficiency and Bruton hypogammaglobulinemia. Normal T-lymphocyte function would be expected with both common variable immunodeficiency and Bruton hypogammaglobulinemia. Rudimentary germinal centers would be found in Bruton hypogammaglobulinemia but not in common variable immunodeficiency. Susceptibility to mucosal surface pathogens would be observed with both common variable immunodeficiency and Bruton hypogammaglobulinemia.

Explanation:

This child has MHC class I deficiency, which causes detect in the development of CD8+cells in the thymus. Because there is no MHC class l, cytotoxic cells cannot be selected, although helper cells (CD4+), which recognize MHC class II molecules, are normally produced.
The gamma-delta T-cell receptor is present on a small proportion of T cells that do not undergo thymic selection. Their function in the body is not known, but they would not be affected by the absence of the class I MHC.
Intercellular adhesion molecule-1 is a molecule found on the surface of antigen- presenting cells in the body that reacts with LEA-1 on T cells for the purpose of cell-to-cell adhesion. Its absence would not affect the development of cells in the thymus. The killer inhibitory receptor is one of two receptors found on the surface of natural killer cells. It inhibits the killing of an attached cell if it is bound to MHC class I. Because this child has normal levels of CD16+ (natural killer) cells, it is unlikely he has a deficiency of this receptor. MHC class II is the molecule that presents peptides that have been processed in intracellular vesicles by antigen presenting cells to T-helper cells. If this molecule were absent from the child, he would be suffering from bare lymphocyte syndrome, which is associated with a failure of education of CD4+ helper cells, not CD8+ cells as described here.

Explanation:

Babesia microti is an intraerythrocytic parasite that causes a mild anemia and fever in affected humans. It is transmitted by the same tick that transmits Lyme disease Ixodes scapularis. Red blood cells are the only cells in the body that are devoid of MHC class I molecules so lysis of these cells by a cytotoxic cell would only be possible using NK cells.
NK cells are the cytotoxic cell that kills in the absence of MHC class I recognition. NK cells are actively inhibited if they recognize these antigens on a target cell. The most specific marker for the identification of NK cells is CD56, although CD16 is also found on their surface. CD4 cells are helper T cells. They assist in both antibody-mediated and cell-mediated immune responses, but by themselves, as stipulated in this question stem, they would not be capable of lysis of red blood cells. CD8 cells are cytotoxic T cells. These cells kill by identifying alterations in the MHC class I molecule. Since such molecules are absent from erythrocytes, cytotoxic T cells are not capable of lysing erythrocytes. CD14 is the endotoxin receptor that is found on macrophages. Macrophages are capable of ingesting and destroying infected erythrocytes in the spleen, but are not capable of causing their lysis in this system. CD16 is the receptor for the Fc component of immunoglobulin G. It is present on a variety of cells, including natural killers, macrophages, and neutrophils. Therefore, it is not the best marker for the NK cell uniquely but would label several populations of cells.

Explanation:

Enlargement of the distal segments of the fingers and toes due to proliferation of connective tissue is known as clubbing. Clubbing maybe associated with lung cancer, mesothelioma, bronchiectasis, and hepatic cirrhosis. In these conditions, the clubbing is accompanied by formation of new subperiosteal bone (hypertrophic osteoarthropathy or hypertrophic pulmonary osteoarthropathy-HPO). Additionally, this patient has emphysema likely due to smoking, which also causes lung cancer. It is now the subject of vigorous debate whether it is the cancer that actually causes HPO or the emphysema, which is often associated with lung cancer. Either way, when HPO is identified, it is incumbent upon the clinician to look for a potential lung cancer. Chronic renal failure causes renal osteodystrophy, which may manifest s combination of osteitis fibrosa cystica and osteomalacia. This is due to elevated parathyroid hormone, which causes the leaching of bones. Multiple exostoses are sometimes associated with multiple colonic polyps and colon cancer in Gardner syndrome. A variety of endocrine adenomas can be seen in polyostotic fibrous dysplasia. The most well known of these is McCune-Albright syndrome: precocious puberty and polyostotic fibrous dysplasia. Profound anemia can be seen in diseases that destroy the marrow, such as ac osteopetrosis, mastocytosis, myelofibrosis, lymphoma, or leukemia.

Explanation:

The most frequent cause of nephrotic syndrome in children is minimal change disease (Iipoid nephrosis), which is characterized by an absence of findings by light microscopy and by fusion of epithelial toot processes on electron microscopy. Dense deposits are seen in type II membranoproliferative glomerulonephritis. Mesangial deposits are a prominent feature of IgA nephropathy and are seen to a lesser degree in several other glomerulonephritides. Subendothelial deposits are seen in type I membranoproliferative glomerulonephritis. Subepithelial spikes are a feature of membranous glomerulonephritis.

Explanation:

Although many of the events that produce atherosclerotic plaques remain elusive, several steps in the process are known. The first gross findings associated with atherosclerotic plaque formation are fatty streaks. Fatly streaks are found in the vasculature of most people in the second decade of life. The fatty streak is a focal accumulation of serum lipoproteins within the intima of the blood vessel wall. As smooth muscle cells migrate to the lesion they produce a connective tissue matrix that overlies the lipid-laden foam cells. When this fibrous covering dislodges, the thrombogenic contents of the lesion are exposed to the circulation and the ensuing clot then occludes the vessels. Tissue ischemia and infarction then occur. The fibrous lesions that follow the fatty streak seldom produce infarction through direct extension of the lesion ischemia may occur with resulting angina, but because the lesion growth is slow, collateral vessels may grow and thus prevent infarction. The fatly streak precedes fibrous lesions found in coronary artery disease. Lipid-laden macrophages, called foam cells, contribute to the core of atherosclerotic lesions. They do not, however, release their lipids through exocytosis, forming a lipid-based occlusion.

Explanation:

Scalded skin syndrome is a pediatric condition caused by an exfoliative toxin produced by Staphylococcus aureus (which is a common cause of cellulitis). The toxin splits the epidermis at the level of the stratum granulosum, causing global denudation of the skin. Scalded skin syndrome is not associated with suntanning or sunburn. Impetigo is a superficial skin infection, usually caused by group A beta-hemolytic streptococci or staphylococci. Classic clues are eroded pustules covered by honey colored crusts. Impetigo may lead to post-streptococcal glomerulonephritis, a sign of which is red cell casts in the urine. Melasma consists of irregular patches of hyperpigmentation on the face. It most commonly appears during pregnancy and may not completely regress. Tinea corporis is a fungal infection. It is also known as “ringworm” because it presents as an expanding round lesion with an erythematous circinate border. Vitiligo is characterized by irregular patchy depigmentation of the skin that exhibits melanocyte deficiency microscopically. It is possibly autoimmune in origin and maybe related to stress. It is not associated with sun exposure and is a chronic condition.

Explanation:

Infectious mononucleosis is a benign infection caused by the Epstein Barr virus (EBV), a herpesvirus. Although B lymphocytes are infected by the virus, the characteristic atypical cells are activated cytotoxic and suppressor T cells-thus the paracortical location (T cell zone) in the lymph node. Lymph nodes in viral infections show expansion of germinal centers without loss of normal architecture. All lymphomas, including Burkitt, Hodgkin, and non Hodgkin lymphomas, destroy the normal architecture of the lymph node. AIDS is associated with a number of neoplastic and infectious processes that may alter the lymph node structure. The characteristic lymph node changes in AIDS are progressive transformation of the germinal centers, not paracortical hyperplasia. Burkitt lymphoma produces a sea of monotonous, mitotically active cells in a “starry sky” appearance. Hodgkin lymphoma also can show nodular or diffuse patterns but is characterized by the presence of Reed-Sternberg cells. Other non Hodgkin lymphomas show either a nodular appearance or diffuse sheets of cells that replace the germinal centers.

Explanation:

Explanation:

This patient has Chagas´ disease, which is endemic to Central American countries.
Infection with Trypanosoma cruzi is transmitted via reduviid bugs and can cause myocarditis, leading to congestive heart failure in its chronic stages.
Diagnosis of acute Chagas´ disease is by examination of the peripheral smear. Diagnosis of chronic Chagas´ disease is by immunofluorescence testing and ELISA. Echocardiogram would only tell us that the patient has cardiomegaly and a low ejection fraction, but not the cause of congestive heart failure. The barium swallow would diagnose achalasia or dilated esophagus secondary to Chagas´ disease. This would cause symptoms of dysphagia. Peripheral smear examination is useful to diagnose acute Chagas´ disease. Acute phase is generally limited to facial edema and nodule (chagoma) near the bite coupled with fever, lymphadenopathy, and hepatosplenomegaly. Cardiac manifestations are associated with the chronic form of the disease in which few trypomastigotes are found in the blood. The electrocardiogram may reveal conduction defects, but the specific diagnosis of Chagas´ disease cannot be made from the electrocardiogram.

Explanation:

Explanation:

Explanation:

Explanation:

Staphylococcus aureus is isolated in 60% of the cases of endocarditis from intravenous drug abuse (IVDA). Streptococci, enterococci, Gram negative bacilli, and fungi are also significant causes.

Explanation:

Melanoma is most commonly associated with which one of the following?

Explanation:

This child has floppy baby syndrome, caused by ingestion of the spores of Clostridium botulinum germination of the organism in the gut of the infant and subsequent production of the botulinum toxin, which causes a flaccid paralysis by blocking release of acetylcholine in cholinergic synapses. The genetic coding for production of this neurotoxin is found in the genome of a lysogenic phage, and therefore is produced only in virus infected bacterial cells. Other medically important attributes that are encoded in this way include the O antigen of Salmonella the erythrogenic exotoxins of Streptococcus pyogenes and the diphtheria toxin. The bacterial chromosome is the location of all essential genes in the bacterium. Loss of any essential gene will result in the death of the organism. Although most exotoxins are encoded on bacterial plasmids, endotoxin production and the cholera toxin are chromosomally encoded. An episome is a plasmid, which has become stably integrated into the bacterial chromosome. This is the mechanism by which Hfr cells arise in nature, but is not known to play a role in exotoxin production in bacteria. Plasmids are extrachromosomal circles of DNA that replicate autonomously and carry genes for most exotoxins, fertility factors, and most antibiotic resistances. The botulinum toxin, the erythrogenic exotoxins of Streptococcus pyogenes, and the diphtheria toxin are not encoded on plasmids, but in the genomes of lysogenic phages. Transposons are mobile segments of DNA, which are capable of mediating their own movement with in and between strands of DNA inside cells. Transposition is believed to be responsible for the arising of multiple drug resistance plasmids, but is not believed to play a role in exotoxin production.

Explanation:

Explanation:

Explanation:

The patient has progressed from being asymptomatic to the point that he has a condition attributed to HIV infection, but not an AIDS defining condition. The most likely CD4 count associated with this stage of disease would be between 200 and 400 cells per mm^3 0-199 would be the expected CD4 cell count of a patient who has progressed to full blown AIDS. Full-blown AIDS is defined by the presence of a variety of infections or conditions that demonstrate a life-threatening collapse of the immune system. Examples of such conditions would include HIV encephalopathy, Pneumocystis pneumonia, Kaposi sarcoma, cryptosporidiosis, or Mycobacterium avium-intracellulare infections.
400-599 is a range of CD4 cell counts that would be associated with a finding of generalized lymphadenopathy or asymptomatic infection. The existence of thrush in the patient described indicates that he has progressed to the early symptomatic phase of the disease. 600-799 is a range of CD4 cell counts that would be expected in an asymptomatic patient, without generalized lymphadenopathy or thrush. Above 800 is considered a normal value for CD4 cells in an uninfected individual.

Explanation:

The best markers for identification of B cells are CD19, CD20, and CD21. The CD21 marker is a receptor for EBV (Epstein – Barr virus). The CD3 marker is present on all T cells with either a CD4 or CD8 marker. This is the marker that is used to identify total T cell count in a blood sample. The CD3 marker is used for signal transduction in the different T cells. The CD4 marker is used to identify T helper cells. These are the cells that recognize exogenous peptides presented on MHC class II molecules by macrophages. CD4+ T helper cells are also involved in cell-mediated delayed hypersensitivity, production of cytokines for stimulation of antibody production by B cells, and stimulation of macrophages. The CD8 marker is used to identity cytotoxic T cells. These are the cells that recognize viral epitopes attached to the MHO class I molecules of a virally infected cell. The CD56 marker is used to identify NK (natural killer) cells. These cells are important in innate host defense, specializing in killing virally infected cells and tumor cells by secreting granzymes and perforins.

Explanation:

Explanation:

Pseudomembranous enterocolitis is caused by the toxins produced by Clostridium difficile. Even if it is difficult to determine the exact antibiotic this patient is currently taking the report of a recently started therapy should instantly make you think of antibiotic associated diarrhea or pseudomembranous colitis. The oral antibiotic this patient is currently taking is clindamycin, which is an antibiotic commonly used (in addition to tetracyclines) for the treatment of moderate to severe acne. As stated in the question, it has a similar mechanism of action and resistance as macrolides and is generally used to treat infections caused by anaerobic and some gram positive organisms. Patients develop fever and abdominal pain, with diarrhea often containing leukocytes and blood. Characteristic features of the disease include the formation of inflammatory, yellow tan pseudomembranes in the colon. The diagnosis is made by the C. difficile toxin assay, and the initial treatment of choice is with metronidazole (an alternative is vancomycin). Gastroenteritis is an acute condition, usually caused by a virus or bacterium that presents with vomiting and diarrhea. There is typically no blood in diarrhea associated with gastroenteritis, and most of these infections are self-limited. There is no association with oral antibiotic intake irritable bowel syndrome is predominantly a pain syndrome of unknown etiology in which there is increased frequency of the normal peristaltic and segmentation contractions of the bowel. It is a chronic condition that produces episodic diarrhea with periods of constipation. Salmonella infection is a common cause of food poisoning. Findings include nausea, vomiting, abdominal pain, and diarrhea often with blood.
Ulcerative colitis is a chronic condition that has features of bloody diarrhea, abdominal pain and weight loss. It is limited to the large bowel, and is exclusively a mucosal disease. Ulcerative colitis involves predominantly the rectum, has no skip lesions (mucosa is affected in its entire extension), and does not cause oral or perianal complications.

Explanation:

The lesion is a port wine stain, a vascular lesion that, unlike the more common strawberry nevus, does not usually regress with age. Port wine stains can be a component of Sturge Weber disease, which can also include similar vascular lesions of the meninges (leptomeningeal angiomatosis) and sometimes cutaneous angiomatosis at other sites. CT of the brain demonstrates a characteristic pattern of hemispheric atrophy thought to be due venous infarction, with tram-track calcification along the cortical ribbon.
Arnold-Chiari malformations are a cluster of related brain and spinal cord malformations in which there is a downward displacement of the cerebellar vermis and tonsils into the foramen magnum. Dandy-Walker malformation includes a distended fourth ventricle with a hypoplastic (or absent) cerebellum.
Neurofibromatosis includes benign and malignant peripheral nerve lesions and café au-lait spots. Tuberous sclerosis includes cortical tubers, adenoma sebaceum of the skin, pancreatic cysts, renal angiomyolipomas, and cardiac rhabdomyomas.

Explanation:

Untreated hypertension leads to hypertrophy of arteries and arteriole. The wall to lumen ratio increases as the walls of the blood vessels thicken. It is not entirely clear why arteries and arterioles hypertrophy in hypertensive patients; however, the vessel walls are subjected to extra amounts of stretch at the higher luminal pressures which may stimulate smooth muscle cell growth. Thus the thickened walls of arteries and arterioles in hypertensive patients is an adaption to the hypertension rather than a cause of the hypertension. The increase in blood pressure that occurs during normal exercise can cause the walls of arteries to thicken (and thus the wall to lumen ratio to increase) when the exercise is frequent, even though the normal resting blood pressure is not necessarily elevated in individuals who exercise regularly. [“Wall to lumen ratio” refers to the ratio of wall thickness to lumen radius or to the ratio of the two cross-sectional areas.] Arteriolar density and capillary density are thought to be decreased in hypertensive individuals. The capillaries lack smooth muscle cells in their walls so the wall to lumen ratio of capillaries does not change. Because the density of capillaries and arterioles decreases in hypertensive individuals the total cross-sectional areas of the capillaries and arterioles are also decreased.

Explanation:

Explanation:

Scalded skin syndrome is a pediatric condition caused by an exfoliative toxin produced by Staphylococcus aureus (which is a common cause of cellulitis). The toxin splits the epidermis at the level of the stratum granulosum, causing global denudation of the skin. Scalded skin syndrome is not associated with suntanning or sunburn. Impetigo is a superficial skin infection, usually caused by group A beta-hemolytic streptococci or staphylococci. Classic clues are eroded pustules covered by honey colored crusts. Impetigo may lead to post-streptococcal glomerulonephritis, a sign of which is red cell casts in the urine. Melasma consists of irregular patches of hyperpigmentation on the face. It most commonly appears during pregnancy and may not completely regress. Tinea corporis is a fungal infection. It is also known as “ringworm” because it presents as an expanding round lesion with an erythematous circinate border. Vitiligo is characterized by irregular patchy depigmentation of the skin that exhibits melanocyte deficiency microscopically. It is possibly autoimmune in origin and maybe related to stress. It is not associated with sun exposure and is a chronic condition.

Explanation:

Lipofuscin is a brown pigment that accumulates with aging. It is believed to be produced from the peroxidation of lipids. Lipofuscin accumulation does not necessarily impair the ability of the cell to function and can be found in the hearts and livers of healthy elderly patients. Beta-carotene is a carotenoid ingested in the diet (found in yellow vegetables such as squash, pumpkins, and carrots) and converted to vitamin A. Excessive beta-carotene can cause a benign yellow orange discoloration of the skin in a condition known as carotenemia. Bilirubin is a pigment derived from the metabolism of the heme group of hemoglobin. As hemoglobin is broken down, it first forms biliverdin, which is subsequently converted to bilirubin. Bilirubin can be conjugated (to glucuronic acid) or unconjugated. The conjugated form (also called the direct reacting portion) accumulates in biliary obstructions. The unconjugated form of bilirubin (indirect reacting) accumulates in hemolytic processes. Hemosiderin is the storage form of iron and stains blue with Prussian blue. Hemosiderin accumulation from breakdown of red cells is seen in chronic passive congestion of the lung (inside hemosiderin-laden macrophages called “heart failure cells”). Hemosiderin deposition is also seen in hemochromatosis, a disorder characterized by abnormal iron storage. Hemochromatosis is seen in patients with increased iron uptake from the gastrointestinal tract and in patients receiving repeated blood transfusion therapy. Melanin is a brown black pigment made by melanocytes in the skin. Melanin is also found in the iris, giving the eye its color. Neuromelanin is a type of melanin found in catecholamine neurons in the brain.

Explanation:

This patient has a history consistent with Boerhaave syndrome. In this syndrome, the patient ruptures the esophagus after episodes of retching. The tear usually occurs 3-5 cm above the gastroesophageal junction, and patients display retrosternal chest pain that may radiate to the back. Signs of the disease may include: left pneumothorax, pleural effusion, subcutaneous or mediastinal emphysema, tachypnea, tachycardia, and signs of infection, if more than 24 hours have elapsed since onset. The aorta, left ventricle, lung, and sternum are not involved in the patient´s condition. A history of retching should direct suspicion away from these other structures.

Explanation:

The autosomal recessive disease is α-1-antitrypsin deficiency, in which an abnormal form of α-1-antitrypsin can be produced by, but not released from, liver cells. This enzyme was named when it was found in vivo to function as a good inhibitor of the pancreatic protease trypsin. However, it actually inactivates a wide variety of enzymes with protease activity that have an essential serine residue in the catalytic centers. Examples of these serine proteases include all of the answer choices, and additionally cathepsin G and plasminogen. Surprisingly, α-1-antitrypsin disease specifically targets only the liver and the lungs. The liver disease, which can be mild to life threatening (either due to cirrhosis or, rarely, massive acute hepatic failure), is related to retained α-1-antitrypsin with residual enzymatic activity. The lung disease seems to be the specific result of an inability to turn off elastase produced by neutrophils during lung infections. Neutrophil elastase is one of the few enzymes that can successfully destroy the heavily crosslinked, insoluble, elastin that is presented in the lung interstitium and contributes to its elasticity. With destruction of this lattice like elastic tissue support structure, emphysema can develop in the lungs. Chymotrypsin is a pancreatic enzyme formed in the intestinal lumen that cleaves aromatic aminoacyl bonds. Plasmin is an enzyme involved in fibrinolysis. Thrombin is an enzyme involved in coagulation. Trypsin is a pancreatic enzyme found in the intestinal lumen that cleaves arginyl and lysyl bonds.

Explanation:

The patient has developed hyperparathyroidism, a well recognized sequela of chronic renal failure. This condition is caused by high levels of serum phosphate and low serum calcium, which stimulate the release of parathyroid hormone (PTH) in an effort to normalize the calcium/phosphate ratio. PTH binding to osteoblasts causes increased expression of RANKL (receptor activator for nuclear factor K ligand), which promotes the differentiation of osteoclast precursors, leading to enhanced bone resorption. This condition, known as renal osteodystrophy, may lead to osteomalacia and osteitis fibrosa cystica, which is classically associated with dissecting osteitis, as described in this question. Calcitonin, which serves to lower serum calcium levels, is produced in small quantities in chronic renal failure, as serum calcium is already pathologically low. Excess cortisol may produce osteoporosis and pathologic fractures, but there is no relationship between chronic renal failure and cortisol excess. Cushing syndrome is generally secondary to adrenal or pituitary adenomas or primary adrenal hyper function. Erythropoietin production is deficient in chronic renal failure. Excess erythropoietin activates erythrocyte precursors but does not activate osteoclasts. Glucagon excess is a very rare entity, occurring in a minority of islet cell tumors, and is not associated with renal failure. High glucagon produces a transitory skin rash, anemia, and a form of diabetes mellitus.

Explanation:

Neonatal respiratory distress syndrome (hyaline membrane disease) occurs in premature infants as the result of a deficiency in pulmonary surfactant (composed primarily of dipalmitoyl lecithin). This is due to inadequate lecithin synthesis by immature type II pneumocytes. It can be diagnosed before birth by analyzing the amniotic fluid: a lecithin:sphingomyelin ratio greater than 2:1 and the presence of phosphatidylglycerol implies lung maturity. The syndrome is the most common cause of death in premature neonates. Risk factors include birth before the 37th week of gestation, birth by cesarean section, and maternal diabetes. Less than 0.5 L of amniotic fluid is the definition of oligohydramnios, which can be associated with renal agenesis. (Failure of the fetal kidneys to pro-duce urine will result in a low amniotic fluid volume.) Alpha-1 antitrypsin deficiency in amniotic fluid is not associated with lung immaturity.
However, deficiency of this enzyme is associated with both emphysema and liver failure in adults. Elevated maternal HbA1c would indicate poor glycemic control in the mother and a potentially increased risk for fetal abnormalities, but it does not serve as direct evidence of lung immaturity. Elevated maternal serum alpha-fetoprotein (AFP) would be expected in fetal neural tube defects. A low maternal AFP is associated with fetal Down syndrome.

Explanation:

Transfusion of blood increases cardiac output by increasing mean systemic tilling pressure (MSFP) and decreasing the resistance to venous return. The dashed curve in the figure shows a venous return curve that is shifted to the right and rotated up ward. The right ward shift is caused by increasing MSFP from a normalvaIueof+7 to +12 mm Hg. The increase in blood volume distends the blood vessels and thereby decreases the resistance to venous return (which causes the venous return curve to rotate upward). Even with no change in the cardiac output function curve, the cardiac output has increased to 15 L/min, as shown in the figure.
The increase in sympathetic stimulation that accompanies exercise constricts venules and veins and thus increases the “tightness” of the circulation, as reflected by an increase in MSFP. Although the dashed venous return curve shown in the figure could very well be attributed to exercise or sympathetic stimulation, both of these perturbations also shift the cardiac output curve (i.e., cardiac function curve) in an upward direction because they both increase myocardial contractility. Hemorrhage causes a reduction in blood volume which decreases MSFP and thus shifts the venous return curve to the left. Also, the cardiac out put curve is shifted downward when hemorrhagic shock decreases myocardial contractility. Spinal anesthesia blocks the sympathetic nervous system, which lowers MSFP (i.e., the venous return curve shifts to the left) and decreases myocardial contractility (i.e., the cardiac output curve shifts downward).

Explanation:

The prevalence of coeliac disease is 1% in western societies, and is thus one of the commonest immune-mediated diseases. It arises as a result of genetic predisposition, at least 95% of patients are HLA-DQ2 or HLA-DQ8 positive, and also from the specific immune response to the alpha-gliadin component of gluten.
Cow´s milk can produce an immunologically mediated enteropathy, but the condition is rare and transient. The action of tissue transaminases on alpha-gliadin generates epitopes to CD4+ T-lymphocytes, which provoke an inflammatory response in the intestinal wall. In untreated individuals, alpha-gliadin specific CD4+ T cells can be found producing interferon-gamma in the intestinal wall.

Explanation:

Gaucher´s and Marfan syndrome do not present with infertility. Noonan´s is associated with short stature. K1inefelter´s is a sex chromosome disorder affecting 1:400 -1:600 male births typically with 47 XXY, XXXYY or XXYY. Andropause is the term for the gradual decrease in serum testosterone concentration with age, but does not occur, usually, until after the age of 50.

Explanation:

Mutation in the fibrillin-1 gene is felt to be responsible for Marfan syndrome. In Marfan syndrome the lack of normal fibrillin-l lease to overactivity of TGF-b in the wall of the aorta and the heart valves, leading to damage and destruction to the connective tissue which weakens that aortic wall and heart valves, causing them to stretch. SPINK1 mutations are present in pancreatitis. HLA-DR3 mutations are seen in Autoimmune hepatitis, Sjogren syndrome, Diabetes Type 1, SLE, etc. FMR-1 in Fragile X Syndrome and Collagen Type V in Ehlers Danlos syndrome.

Explanation:

A 25-year-old man presents with dark urine, especially in the early morning. Further investigations show that he has haemoglobinuria and haemolyticanaemia. A diagnosis of paroxysmal nocturnal haematuria is made. What is the likely mechanism underlying this condition?

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Explanation:

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Explanation:

The level of HDL is inversely associated with the risk of atherosclerosis. All of the other states are associated with increased atherogenesis.

Explanation:

Staphylococcus aureus is the most common cause of septic arthritis in older children and adults, while group B Streptococci and Escherichia coli are important in neonates.

Explanation:

Henoch Schonlein purpura is a vasculitis disorder associated with immune complexes.

Explanation:

Primary amyloidosis, or amyloidosis that occurs as a result of multiple myeloma, is associated with macroglossia (tongue), peripheral neuropathy (nerves), arrhythmias (heart), and skin manifestations. Spleen involvement is seen in secondary amyloidosis.

Explanation:

Wernicke Korsakoff´s psychosis is a form of psychosis in which confabulation plays a major role. It is most often associated with chronic alcoholism. It is not observed in encephalitis or meningococcemia. The patient´s paresthesias are consistent with a peripheral neuropathy but are not typical of carpal tunnel syndrome or mononeuritis multiplex, neither of which would cause psychosis.

Explanation:

A 54 year old woman has fatigue, trouble sleeping, and feels “sore all over.” She has no synovitis, but expresses pain upon palpation of multiple parts of her trunk and extremities. Remaining examination is unremarkable. Her rheumatoid factor, antinuclear antibody titers are negative, and her ESR is normal. Her serum analysis is also normal. The most likely diagnosis is

Explanation:

Poliovirus is an acute illness produced by three antigenically different strains. Although immunity to each of the three types is life long, infection with one strain does not confer protection against subsequent infection by another strain. Polioviruses are resistant to lipid solvents and stable at a low pH because they lack a lipid envelope. The virus is acquired by the oral route. It subsequently replicates in the oropharynx and lower gastrointestinal tract. Following replication and spread to the local lymphatics, a viremia occurs, with spread to the nervous system. Within the central nervous system, the virus disseminates along neural pathways. Motor neurons are principally affected, primarily in the spinal cord, lower brain stem, and brain stem reticular formation.

Explanation:

Acne has not been shown to be a risk factor in basal cell or squamous cell skin cancer. Individuals with fair complexions and blond hair are more prone to sunburns and subsequent skin cancer. This is thought to be due to less protection from sunburn due to a lower quantity of melanin pigment in the skin. Chronic UV exposure from the sun is a risk factor for skin cancer. Previous bums or scars are a predisposing factor for skin cancer (called scar carcinomas). Exposure to previous ionizing radiation or inorganic arsenic can be a risk factor for skin cancer.

Explanation:

Primary sclerosing cholangitis is associated with ulcerative colitis, and this disease is more common in males. Some patients present with cirrhosis; others with hepatosplenomegaly. The combination of cirrhosis and portal hypertension suggests end stage disease. Primary biliary cirrhosis is more common in middle aged women, and there is no association with ulcerative colitis. Jaundice is rare. This patient is too young for cholangiocarcinoma, which is seen mainly in the elderly Patients with cholecystitis present initially with right upper quadrant pain and fever. Acute schistosomiasis presents with intense pruritis and, in some cases portal hypertension and hepatic fibrosis. There is no association with ulcerative colitis.

Explanation:

Explanation:

CD8+ cytotoxic T cells are stimulated by the presence of endogenously produced peptides presented in the groove of a class I MHC molecule. In the presence of costimulatory molecules such as B7 and CD28, these killer cells can be stimulated directly in the absence of TH cells. The test performed in the microtiter plate here is a cytotoxicity assay to define the class I haplotype of the cancer patient. Cells exposed to specific anti-class I antisera plus complement will become leaky and take up dye molecules. The haplotype of this patient is HLA-A1/7, HLA-B1/7, and HLA-C2/3, so any of these MHC molecules loaded with peptides from the intracellular virus would stimulate a killing response. The peptides loaded into the groove of the class I molecule must be endogenously synthesized: Whole virus will not be effective. EBNA is a molecule found on the membrane of Epstein-Barr virus transformed cells and would be a good candidate for CTL recognition. Whole EBV by itself would not serve as a stimulus for cytotoxic killing. Small peptides produced during viral infection and transported to the cell membrane in the groove of class I MHC molecules serve as the stimulus for this response. HLA-A1/7 by itself would not serve as a stimulus for cytotoxic killing in this patient. This haplotype is syngeneic for the patient and would not be recognized by itself as foreign. HLA-B2/3 would stimulate a cytotoxic response in this patient, but not one which would be directed against EBV-transformed cells. This haplotype is allogeneic to the patient, so it would stimulate a cytotoxic response, but not the desired one. HLA-C2/3 would not serve as a stimulus for cytotoxic killing in this patient. This haplotype is syngeneic for the patient and would not be recognized as foreign.

Explanation:

The most frequent cause of nephrotic syndrome in children is minimal change disease (Iipoid nephrosis), which is characterized by an absence of findings by light microscopy and by fusion of epithelial toot processes on electron microscopy. Dense deposits are seen in type II membranoproliferative glomerulonephritis. Mesangial deposits are a prominent feature of IgA nephropathy and are seen to a lesser degree in several other glomerulonephritides. Subendothelial deposits are seen in type I membranoproliferative glomerulonephritis. Subepithelial spikes are a feature of membranous glomerulonephritis.

Explanation:

Chronic inflammatory conditions, such as collagen vascular diseases, rheumatoid arthritis, and bronchiectasis, may lead in time to accumulation of a specific form of amyloid known as AA (amyloid associated protein). Systemic amyloidosis affects many organs, especially the heart, kidneys, spleen, GI tract, liver, and tongue. The ventricular walls become thickened and inelastic, and the resulting pathophysiologic picture is that of restrictive cardiomyopathy. Congestive heart failure ensues because of decreased ventricular compliance and secondary reduced stroke volume. Note how the ventricular lumina are narrowed and the walls are extremely thickened. A waxy texture is highly suggestive of amyloid deposition which can be confirmed histologically by using Congo red staining. Atherosclerosis of coronary arteries may give three different types of clinical manifestations: arrhythmias (with sudden death), angina pectoris, and myocardial infarction. Loss of myocardial tissue due to ischemic necrosis may lead to congestive heart failure. The heart will show evidence of old infarcts in the form of scars, and the ventricular cavities will become dilated.
Coxsackievirus myocarditis is the most common etiologic form of viral myocarditis, which may resolve without clinical consequences or lead to dilated cardiomyopathy and heart failure. Mutations of myosin chain genes are the most common causes of hypertrophic cardiomyopathy. This manifests with thickening of the interventricular septum (so called asymmetric cardiac hypertrophy), with resultant impediment to both systolic outflow and diastolic filling. Here, the ventricular walls are uniformly thickened and the remaining postmortem findings (liver, kidney, and spleen changes) cannot be explained based on a diagnosis of hypertrophic cardiomyopathy. Systemic hypertension in the early stages is associated with cardiac hypertrophy, but progressive ventricular dilatation develops with decompensation. In a patient dying of hypertension related heart failure the heart is usually large (hypertrophic) and the ventricles are markedly dilated.

Explanation:

Although many of the events that produce atherosclerotic plaques remain elusive, several steps in the process are known. The first gross findings associated with atherosclerotic plaque formation are fatty streaks. Fatly streaks are found in the vasculature of most people in the second decade of life. The fatty streak is a focal accumulation of serum lipoproteins within the intima of the blood vessel wall. As smooth muscle cells migrate to the lesion they produce a connective tissue matrix that overlies the lipid-laden foam cells. When this fibrous covering dislodges, the thrombogenic contents of the lesion are exposed to the circulation and the ensuing clot then occludes the vessels. Tissue ischemia and infarction then occur. The fibrous lesions that follow the fatty streak seldom produce infarction through direct extension of the lesion ischemia may occur with resulting angina, but because the lesion growth is slow, collateral vessels may grow and thus prevent infarction. The fatly streak precedes fibrous lesions found in coronary artery disease. Lipid-laden macrophages, called foam cells, contribute to the core of atherosclerotic lesions. They do not, however, release their lipids through exocytosis, forming a lipid-based occlusion.

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Explanation:

This patient has systemic sclerosis, also called scleroderma. Antibodies to topoisomerase I (anti-Scl-70) occur in up to 70% of patients with diffuse systemic sclerosis, but only rarely in other disorders. Systemic sclerosis, is characterized initially by excessive fibrosis and edema of the skin, especially the hands and fingers, producing sclerodactyly (characteristic changes in the fingers, which resemble claws). Raynaud phenomenon is common. The diffuse type of systemic sclerosis generally spreads to include visceral organs, such as the esophagus (producing dysphagia), the lungs (producing pulmonary fibrosis), the heart (leading to heart failure or arrhythmia), and the kidneys (renal failure causes 50% of scleroderma deaths). Females are affected more than males (3:1 ratio). A more restricted variant of systemic sclerosis, with a somewhat more benign course, is CREST syndrome (Calcinosis, Raynaud syndrome, Esophageal dysmotility, Sclerodactyly, and Telangiectasia), characterized by the presence of anti-centromere antibodies (although 10% of CREST patients will have anti-topoisomerase antibody as well). Anti-ds DNA and anti-Sm (Smith antigen) are characteristic of systemic lupus erythematosus (SLE) but are not common in patients with systemic sclerosis. Rheumatoid factor is an autoantibody directed against IgG. It is found in patients with rheumatoid arthritis. Anti-SS-A is typically seen in Sjögren syndrome (although it may also be seen in SLE).

Explanation:

This patient has disseminated gonococcal infection. Gonococcal arthritis and tenosynovitis typically involve both the upper and lower extremities equally. Vesicular skin lesions are characteristic of disseminated gonococcal disease. Females are at particular risk of gonococcemia during menstruation, since sloughing of the endometrium allows access to the blood supply, necrotic tissue enhances the growth of Neisseria gonorrhoeae, and there is an alteration of the pH. Patients who have a C6-8 deficiency have both an increased risk of gonococcemia and a tendency to have multiple episodes. These patients are also at risk for bacteremia from Neisseria meningitides. Cl esterase inhibitor deficiency can occur as an autosomal dominant disorder or may be acquired. Patients have angioedema without urticaria. The syndrome is also associated with recurrent attacks of colic and episodes of laryngeal edema. Ciliary dysfunction is a marker of Kartagener syndrome (immotile cilia syndrome). The syndrome includes infertility, bronchiectasis, sinusitis, and situs inversus. It is an autosomal recessive disorder caused by abnormalities in the dynein arm of the cilia. Endothelial adhesion molecule deficiency, or beta-2 integrin deficiency, is characterized by failure of neutrophils to express CD18 integrins on their surface. Patients have impaired phagocyte adherence, aggregation, chemotaxis, and phagocytosis of C3b-coated particles. Clinically, there is delayed separation of the umbilical cord, sustained agranulocytosis, recur-rent infections of skin and mucosa, gingivitis, and periodontal disease. Eosinophil deficiency or eosinopenia occurs with stressors such as acute bacterial infection and following administration of glucocorticoids. There is no known adverse effect of eosinopenia.

Explanation:

Bacillus cereus produces a self limited diarrhea due to ingestion of the preformed enterotoxin in contaminated fried rice and seafood. The incubation period is typically around 4 hours. The degree of vomiting is greater than the diarrhea. B. cereus is also associated with keratitis, producing a corneal ring abscess. Clostridium botulinum produces a neurotoxin that blocks the release of acetylcholine, resulting in a symmetric descending paralysis that may lead to respiratory complications causing death. Symptoms include blurred vision, photophobia, dysphagia, nausea, vomiting, and dysphonia. Most cases are associated with the ingestion of contaminated home canned food. Clostridium perfringens produces a severe diarrhea with abdominal pain and cramping (sometimes called “church picnic” diarrhea). The incubation period is 8-24 hours after ingesting contaminated meat, meat products, or poultry. The meats have usually been cooked, allowed to cool, and then warmed, which causes germination of the clostridia) spores. EHEC-Enterohemorrhagic Escherichia coli, produces a bloody, noninvasive diarrhea due to the ingestion of verotoxin found in undercooked hamburger at fast food restaurants. The O157:H7 serotype typically produces this syndrome. Some patients develop a life threatening complication called hemolytic-uremic syndrome. Vibrio cholerae typically produces a watery, nonbloody diarrhea with flecks of mucus (rice water stools). Abdominal pain is not a feature. Massive fluid loss and electrolyte imbalance are complications. Patients who ingest contaminated shellfish experience fever, copious watery diarrhea, and abdominal cramps within 48 hours after eating.

Explanation:

The disease presented in this question is poliomyelitis which is caused by the poliovirus, a picornavirus. The virus is spread via the fecal oral route and can then cause paralysis by infecting the alpha-motor neurons of the anterior horn of the spinal cord. Early symptoms include malaise, headache, fever, nausea, abdominal pain, and sore throat. Later symptoms include flaccid paralysis, muscle atrophy, fasciculations, and areflexia. The central canal has no nerve fibers inside. The corticospinal tract contains upper motor neurons. A lesion of this tract would lead to upper motor neuron symptoms, such as ipsilateral spastic paresis and hyperreflexia. The dorsal columns are a common target of syphilis, a condition known as tabes dorsalis. Dorsal root ganglia contain the neuronal cell bodies of sensory neurons, not motor neurons. The spinothalamic tract has sensory nerve fibers responsible for pain and temperature.

Explanation:

The pathologic picture is classic for papillary necrosis. This complication develops most commonly in diabetic patients, but other conditions may result in this renal complication. Among these, analgesic abuse, urinary tract obstruction, and sickle cell disease are the most important. Papillary necrosis may lead to acute renal failure. Fragments of tissue that slough off necrotic papillae may become impacted into the ureters and cause ureteral colic. Gout may cause two renal complications: interstitial nephritis due to deposition of urate crystal within the renal interstitium, and formation of urate calculi within the pelvis. Miliary tuberculosis often involves the kidney. Tubercular infection will give rise to whitish, seedlike nodules most apparent in the renal cortex and consisting of caseating granulomas. Mural thrombosis in the heart frequently leads to systemic thromboembolism. Consequently, embolic infarcts develop in peripheral organs, including kidney, spleen, brain, and the heart itself. In the kidneys, infarcts manfiest grossly as wedge shaped areas of pale coagulative necrosis in the cortex. Recent streptococcal infection may be associated with postinfectious glomerulonephritis (manifesting with nephritic syndrome). The kidneys are edematous and enlarged, and microscopically there is acute glomerulonephritis.

Explanation:

The infant has congenital syphilis. The tibial deformity develops when spirochetes localize in the periosteum, where they produce an active inflammation with many plasma cells. This then causes a massive, reactive, periosteal deposition of bone on the medial and anterior surfaces of the tibia (“saber shin”). “Saddle nose” deformity, another feature of congenital syphilis, is due to inflammatory destruction of the nasal and palatal bones. Gummas, in which a central necrotic focus is surrounded by layers of granulomatous and nonspecific chronic inflammation, can also be found in and near the saber shin and saddle nose. The bone changes are not neoplastic, and involvement of the medulla and cortical layer of the bone is less marked than are the periosteal changes.

Explanation:

11β-HSD is responsible for the conversion of cortisol to the inactive cortisone, preventing activation of the mineralocorticoid receptor by cortisol but permitting activation by aldosterone. Both Liquorice and Carbenoxolone inhibit 11β-HSD and produce pseudohyperaldosteronism with hypertension and hypokalaemia yet appropriately low renin and aldosterone concentrations.

Explanation:

Leptin is synthesised within the adipocyte and plasma concentrations are directly related to adipocyte (fat) mass. It acts on centres within the hypothalamus to produce satiety.

Explanation:

Liver enzymes are elevated in most patients.
Visual disturbances are suggestive of temporal arteritis not PMR, and are due to ischaemic changes in ciliary arteries (optic neuritis/infarction) and less commonly due to central artery occlusion. Raised CK occurs in polymyositis. PMR is rare before the age of 50 years.

Explanation:

The hepatitis D virus, or delta agent, is a defective RNA virus which cannot replicate except in the presence of hepatitis B virus. Consequently, it occurs as a co-infection or, in the presence of chronic HBV infections, as a superinfection. Hepatitis C can lead to chronic hepatitis in 30-40% of cases. It is usually transmitted via blood transfusions and intravenous needles. It is not associated with hepatitis D. Hepatitis A rarely becomes chronic or aggressive. Hepatitis A is transmitted via the fecal-oral route. Alcoholic hepatitis is associated with the same symptoms as presented in this patient, plus right upper quadrant pain and several other symptoms that make it difficult to distinguish alcoholic hepatitis from extrahepatic biliary obstruction. Hepatitis D Virus is irrelevant to Schistosomiasis.

Explanation:

Microangiopathic hemolytic anemia, thrombocytopenia, elevated serum LDH levels, and normal coagulation test are present in both thrombotic thrombocytopenia purpura and hemolytic-uremic syndrome. However, neurologic abnormalities are typically present only in TTP not HUS.

Explanation:

The lesion described is a hydatidiform mole, of which two forms exist, complete and partial. In a complete mole, the karyotype is 46, XX (or, in a few cases, 46, XY). In this form, fetal tissue is not identified. The most common presenting symptom is vaginal bleeding. Serum hCG levels are dramatically increased and the uterus is enlarged. Hyperemesis can occur in patients with complete moles, probably due to the extremely high hCG levels, but is rare in patients with partial moles. The chorionic villi have a characteristic grapelike, multicystic appearance. It is important to note that unlike the partial mole, which very rarely develops into choriocarcinoma, complete moles carry a 2% increased risk for the development of choriocarcinomas.
This represents a postfertilization event with either a diploid or triploid genotype rather than, haploid (choice A). The disease is unrelated to Turner syndrome, XO (choice B)
A complete mole contains the normal number of chromosomes, and does not contain an additional single Y chromosome (choice D)
In a partial hydatidiform mole, fetal tissue is often evident. The conceptus is triploid, with a 69, XXX or 69, XXY karyotype (choice E). Both enlarged and normal villi are present.

Explanation:

Klinefelter´s syndrome is most often due to the 47, XXY karyotype. It is not the result of low testosterone synthesis (A), testosterone resistance (B), 45Y/47, XXY mosaicism (D), or 47, XXX/47, XXY mosaicism (E).

Explanation:

CA-125 may be elevated in ovarian epithelial tumors, such as a cystadenocarcinoma. AFP can be elevated with either an endodermal sinus tumor or embryonal carcinoma. An elevated hCG can be seen with choriocarcinomas. Sertoli-Leydig and granulosa-theca cell tumors do not usually produce an elevated CA- 125, AFP, or hCG level.

Explanation:

Glucose 6 phosphate dehydrogenase deficiency is an X linked disease present in approximately 15% of all black males in America. It is typically unsymptomatic until challenged with a drug agent which may cause hemolysis, such as primaquine, quinidine, or sulfonamides.

Explanation:

Some studies have suggested that minimal consumption of alcohol might actually be beneficial in reducing atherosclerosis. Cigarette smoking, hypertension, elevated serum cholesterol levels, and a family history of coronary artery disease are all well described risk factors

Explanation:

The diagnosis of pseudogout is often mistaken with other disease states, such as hyperparathyroidism, hypothyroidism, hemochromatosis, and hypomagnesemia. However, the presence of linear calcifications on the surface of articular cartilage in affected arthritic joints is only characteristic of pseudogout, or calcium pyrophosphate deposition disease.

Explanation:

During their development, progenitor B and T lymphocytes undergo complex gene segment rearrangements that allow them to create a wide diversity of antigen recognition molecules. In the case of a B lymphocyte, three gene segments (V, D, and J) are randomly recombined to create the coding for the variable domain of the heavy chain of immunoglobulin. Two gene segments (V and J) are randomly recombined to create the coding for the variable domain of the light chain of immunoglobulin. Analogous rearrangements are made in T cells to create the variability of the N-terminal domains of the T-cell receptor beta or alpha chains (respectively). In order to determine the maximum number of distinct idiotypes (antigen combining sites) in this question, you simply multiply the different possible choices: for the heavy chain, 200 x20 x50, or 2 x 10^5 possibilities; for the light chain, 100 x 10, or 1 x 10^3 possibilities. Since heavy and light chains randomly associate following rearrangement, the product of the two possibilities (2 x10^5) x (1 x10^3), or 2 x 10^8 gives the total number of possible combinations. Option A, 1,000 is not correct. This is the number of distinct light-chain variable domains that could be produced. Option B 4000, is not correct. This is the product of they and D gene segment rearrangements only for the heavy chain. Option C, 1 x 10^4, is not correct. There is no way to arrive at this figure by multiplying combinations of VDJ gene segments. Option D, 2 x 10^5, is not correct. This is the total number of heavy-chain variable domains that could be produced, but an immunoglobulin idiotype consists of both heavy and light-chain variable domains.

Explanation:

Sensitization to latex has become a major health-care problem. Local skin irritations are common but more severe allergic reactions occur, up to and including rare anaphylactic reactions that are occasionally fatal. The immune responses to latex are immediate-type hypersensitivity (type I) reactions, expressing themselves in minutes, and/or delayed-type hypersensitivity (type IV) reactions, which will express themselves in 48 to 72 hours. The type I reactions are due to IgE-mediated sensitivity to latex proteins, whereas type IV reactions are due to a cell-mediated response to the chemicals that are added in the processing of latex. The type IV response in this circumstance would be referred to as contact dermatitis. Irritant dermatitis can be observed in the early stages of sensitization and can be due to sweating, rubbing, and residual soap. In the present case, the timing of the reaction after 72 hours points to the type IV reaction rather than an irritant dermatitis. A type I reaction would have been apparent in minutes with characteristic rhinitis, conjunctivitis, urticaria, asthma, angioedema, or anaphylaxis after the technician put on her latex gloves. A type II reaction is a cytolytic response mediated by an antibody. The type II reaction is observed in the context of hemolytic anemias, thrombocytopenia, neutropenia, etc. A type III reaction is an immune complex response that sets into motion an inflammatory response.

Explanation:

Urticaria (hives) is a good example of a local anaphylaxis reaction which is classified as a type I hypersensitivity reaction. Type I hypersensitivity reactions involve preformed IgE antibody bound to mast cells or basophils, which release vasoactive and spasmogenic substances when they react with antigens. The eosinophil-mediated cytotoxicity against parasites is an example of antibody-dependent, cell-mediated cytotoxicity. Type II hypersensitivity is caused by autoantibodies against cells or tissues. When these antibodies activate complement or promote phagocytosis, the tissue is damaged. Type III hypersensitivity is caused by immune complex deposition in the small diameter blood vessels and the subsequent activation of complement and destruction of the vasculature. The tuberculin (PPD) reaction, used to test for tuberculosis exposure, is an example of delayed-type, or type IV, hypersensitivity.

Explanation:

CD4 and CD8 are both markers for T cells, and mature T cells usually express one or the other but not both. However some of the immature T cells in the thymus (that can “leak” into the baby´s blood in small numbers) coexpress these markers, before the cells have “committed” to being either helper T or cytotoxic T cells. In adults, significant numbers of cells coexpressing CD4 and CD8 usually implies the existence of a non-Hodgkin lymphoma with a cell population similar to immature T cells. Normally T-cell precursors entering the thymus are double positive for CD4 and CD8. During thymic selection, cells that recognize MHC class II become CD4-positive only and differentiate into helper T lymphocytes; whereas cells that recognize MHC class I become CD8 positive only and differentiate into cytotoxic T lymphocytes.
Helper T cells are CD4+ and CD8-, suppressor T cells are CD4- and CD8+. Immature B cells and plasma cells will be both CD4- and CD8-, since these are T-cell markers.

Explanation:

Diagram D shows a disturbance in body fluid balance referred to as “hypertonic contraction” which is characteristic of loss of hypotonic fluid from the body. Loss of hypotonic fluid decreases total body water and increases body fluid osmolarity, as indicated in this diagram. Normal function of the thirst center ensures that polyuria (excessive urine output) closely matches polydipsia (excessive water intake) so that dehydration does not occur. However, when adequate replenishment of water loss by excretion is interfered with (i.e., during surgical procedures), dehydration may become severe, causing fever, psychic disturbances, and even death. The plasma sodium concentration of 175 mEq/L in this patient is a clear indication that he is dehydrated and that serum osmolarity is elevated (extracellular osmolarity can be approximated as 2 times the plasma sodium concentration, which is 350 mOsm/L). Option A (isotonic contraction) can be caused by loss of isotonic fluid, e.g., acute diarrhea. Option B (hypertonic expansion) can be caused by excessive intake of sodium chloride without the drinking) of water. Option C (hypotonic contraction) is characteristic of sodium chloride loss from the body, e.g., secondary to lack of aldosterone.
Option E (hypotonic expansion) can be caused by retention of water by the kidneys, e.g., inappropriate secretion of antidiuretic hormone.

Explanation:

This patient most likely has Huntington disease. The caudate degenerates markedly in this disease although the putamen and nucleus accumbens also degenerate. Atrophy of the caudate and putamen can make the lateral ventricles appear very large when imaged. Bradykinesia, resting tremor, and difficulty initiating movements are typical of Parkinson disease, which results from midbrain substantia nigra degeneration. Intention tremor and akinesia are signs of cerebellar dysfunction. Moon facies, amenorrhea, and hypertension are typical of Cushing syndrome. Additional symptoms include truncal obesity, increased facial hair, acne, irritability, depression, and decreased energy. This can be caused by an ACTH-secreting pituitary adenoma. Motor and vocal tics are indicative of Tourette syndrome.

Explanation:

There are four types of myeloproliferative disorders: chronic myeloid leukemia (CML), polycythemia vera, myeloid metaplasia with myelofibrosis (MMM), and essential thrombocythemia (which is very rare). Both CML and polycythemia vera are characterized by hypercellular bone marrow producing all three cell lines. Over a period of years, the bone marrow may burn out, and the marrow space is replaced by fibrosis. In this circumstance, hematopoiesis (including production of neoplastic cells) moves to extramedullary sites, predominantly the spleen and liver. This process is called myeloid metaplasia with myelofibrosis. Polycythemia vera does not involve the lymphoid cell line, so progression to lymphoid malignancies such as acute lymphoblastic leukemia, chronic lymphocytic leukemia, multiple myeloma or Waldenstrom macroglobulinemia is unlikely. Although both polycythemia vera and CML can progress to MMM polycythemia vera does not progress to CML. Hairy cell leukemia a leukemia often associated with massive splenomegaly, is derived from a B lymphocyte, not a myeloid stem cell. It would not progress to a myeloproliferative disorder.

Explanation:

The primary function of blood vessels in skeletal muscles is to supply nutrients and remove metabolic waste products from the muscle tissues. Prolonged increases in metabolic rate lead to growth of the vasculature; decreases in metabolic rate lead to vascular rarefaction, i.e., loss of capillaries as well as other types of blood vessels. In other words, blood vessels grow where they are needed and regress when they are not needed. When a limb is immobilized in a cast, the muscles are inactive and their metabolic rate decreases. This decrease in metabolic rate leads to a decrease in capillarity in the skeletal muscles by mechanisms that are poorly understood. When the metabolic rate of immobilized skeletal muscle decreases, the oxygen consumption of the muscle decreases, which is likely to cause an initial increase in both myoglobin oxygen saturation and intracellular pO2. Vascular endothelial growth factor (VEGF) is thought to stimulate the angiogenesis caused by exercise training. Immobilizing skeletal muscle would be expected to decrease VEGF production.

Explanation:

Explanation:

This patient has aortic stenosis. In aortic stenosis, the blood is ejected from the left ventricle through a smaller-than-normal opening. Because the resistance to ejection of blood is high, the left ventricular pressure can sometimes increase to over 250 mm Hg with normal systolic pressure in the aorta. Note that in this patient, the left ventricular peak systolic pressure has increased to 170mm Hg, the aortic systolic pressure is normal at 120 mm Hg, and a 50mm Hg gradient exists across the aortic valve during systole. In aortic regurgitation, blood flows backward through the aortic valve during diastole when the valve is closed. Left ventricular systolic pressure and aortic systolic pressure are nearly the same with pure aortic regurgitation. Mitral regurgitation means there is backward flow of blood through the mitral valve during systole. This accumulation of extra blood in the left atrium during ventricular systole leads to an elevation in the pulmonary wedge pressure (which is used as an estimate of left atrial pressure). In mitral stenosis, blood must flow from the left atrium into the left ventricle through a smaller-than-normal opening. Because the resistance to blood flow through the mitral valve is higher than normal, the left atrial pressure (estimated by the pulmonary wedge pressure) is often several mm Hg higher than the left ventricular end diastolic pressure. Right-sided heart failure is most commonly due to left-sided heart failure: blood simply backs up through the lungs and into the right heart. However, this patient has not yet developed right heart failure. All of the pressure recordings in the right heart and lungs are normal. Note i that if one undergoes cardiac catheterization, only arterial pressures (left-sideds can be obtained. One must access the venous-side for right-sided pressures. Pulmonic regurgitation would result in a high wedge pressure.