USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 251:

  A 64-year-old man with long-standing hypertension experiences severe abdominal pain and loses consciousness. He dies en route to the hospital. Significant autopsy findings include dilation of the aorta just above the iliac bifurcation and massive abdominal hemorrhage. Which of the following was most likely the initiating event that resulted in his fatal lesion?

  A. antibody-mediated endothelial damage

  B. autosomal dominant inheritance of an abnormal gene on chromosome 15

  C. intimal proliferation with fibrous cap formation

  D. luminal narrowing of the vasa vasorum leading to medial degeneration and fibrosis

  E. ossification of calcific deposits in the tunica media

  Correct Answer: C

  Section: Pathology and Path physiology This man had a ruptured abdominal aortic aneurysm. Most commonly, this is the result of severe atherosclerotic changes that lead to weakening, dilation, and possible rupture of the affected aorta. (In this case, the hypertension would have accelerated the atherosclerotic changes and increased the likelihood of rupture of the aneurysm.) Initial vascular changes found in atherosclerosis include intimal thickening and fibrous cap formation. Antibodymediated endothelial damage (choice A) is a common cause of vasculitis but is not involved in atherosclerosis. Of the diseases that result from autosomal dominant inheritance of an abnormal gene on chromosome 15 (choice B), the most common is probably adult polycystic disease but this has no bearing on the development of atherosclerosis. Luminal narrowing of the vasa vasorum leading to medial degeneration and fibrosis (choice D) is seen in the development of a syphilitic aortic aneurysm but has no role in this patient's disease process. Ossification of calcific deposits in the tunica media (choice E) and other areas of dystrophic calcification may occur as a complication of atherosclerotic plaques, but even if present in this patient, this process would not represent the initiating event.

• Question 252:

  The changes seen in the kidney shown in below figure were an incidental finding in the autopsy of a 39year-old woman. The most likely cause is which of the following?

  

  A. abuse of analgesics

  B. hypertension

  C. postrenal obstruction

  D. renal cell carcinoma

  E. renal infarct

  Correct Answer: C

  Section: Pathology and Path physiology The kidney in figure demonstrates severe hydronephrosis characterized by dilation of the renal pelvis at the expense of the subadjacent renal medulla and cortex. Postrenal obstruction, such as a ureteral stone, is the most likely etiology. Abuse of analgesics (choice A) may be associated with necrosis of the renal papillae. The papillae in the photo are not necrotic. Hypertension (choice B) mainly affects the blood vessels of the renal cortex, sparing the pelvic region of the kidney. Renal cell carcinoma (choice D) displays a yellowish cortical-based tumor, not hydronephrosis. An acute renal infarct (choice E) demonstrates a pale, wedge-shaped area with its base along the renal capsule. A chronic infarct shows either fibrous scarring or cyst formation. The renal pelvis is usually unaffected by renal infarcts.

• Question 253:

  A 19-year-old freshman football player collapses during preseason workouts on a very hot afternoon. He has no significant prior medical history other than a recent upper respiratory infection. He is taken to the emergency room but cannot be revived. An autopsy reveals an enlarged heart that, on microscopic examination, shows myocyte disarray. Which of the following was the most likely cause of death?

  A. alcoholism

  B. cardiac amyloidosis

  C. heat stroke

  D. hypertrophic cardiomyopathy

  E. viral myocarditis

  Correct Answer: D

  Section: Pathology and Path physiology Hypertrophic cardiomyopathy often presents with dyspnea and chest pain. Arrhythmias are a common problem in these individuals and sudden death, particularly after very strenuous exercise, can occur. There is good evidence that at least half of these cases are familial--probably autosomal dominant. Adistinctive microscopic finding is myocyte disarray. Alcoholism (choice A) can produce dilated cardiomyopathy which does not show myocyte disarray. Cardiac amyloidosis (choice B) would not be expected in a young adult with no history of chronic disease and would show interstitial hyaline deposits of amyloid microscopically. Heat stroke (choice C) is marked by a lifethreatening increase in core temperature and would not produce the changes described above. Viral myocarditis (choice E) can produce an enlarged flabby heart but does not have myocyte disarray

• Question 254:

  A 74-year-old woman with left heart failure develops pulmonary edema. This accumulation of fluid is best explained by which of the following mechanisms?

  A. decreased hydrostatic pressure

  B. decreased lymphatic drainage

  C. decreased oncotic pressure

  D. increased hydrostatic pressure

  E. increased lymphatic drainage

  F. increased oncotic pressure

  Correct Answer: D

  Section: Pathology and Path physiology In left-sided heart failure, poor chamber contractility results in impaired systolic outflow, creating an increase in end diastolic volume and a corresponding increase in ventricular hydrostatic pressure. Impaired ventricular emptying causes stasis in the pulmonary circulation, resulting in a similar increase in volume and pressure in the microvasculature. Capillary congestion leads to widening of endothelial intercellular junctions, leakage of fluid into the interstitium/ alveoli, and the formation of pulmonary edema. Decreased hydrostatic (choice A) and oncotic (choice C) pressures and increased lymphatic drainage (choice E) theoretically would reduce total blood volume, thus acting to retard, not induce, pulmonary edema. Decreased lymphatic drainage (choice B) and increased oncotic pressure (choice F) could potentially lead to pulmonary edema; however, they would be secondary factors in cases of left heart failure, as increased hydrostatic pressure is directly responsible for the accumulation of fluid in the lungs.

• Question 255:

  A 26-year-old man is found dead in his apartment. A neighbor, who had seen him the previous day, said that he appeared to be perfectly healthy at that time. The coroner performs an autopsy and the only significant finding is hyperinflation of the lungs with areas of atelectasis and thick mucus in the bronchioles. Microscopically, there is thickening of the bronchial epithelial basement membranes, hyperplasia of submucosal mucous glands and bronchial smooth muscle, and infiltration by eosinophils. All of these findings are consistent with which of the following diagnoses?

  A. adult respiratory distress syndrome

  B. bronchiolitis obliterans--organizing pneumonia

  C. chronic bronchitis

  D. emphysema

  E. status asthmaticus

  Correct Answer: E

  Section: Pathology and Path physiology Characteristic microscopic findings in asthma are thickened basement membranes, hyperplasia of bronchial smooth muscle, hyperplasia of submucosal mucous glands, and the presence of eosinophils, all of which were seen in this case. The hyperinflation of the lungs and mucous plugging are common gross findings in someone dying in status asthmaticus. The principal microscopic finding in adult respiratory distress syndrome (choice A) is the formation of hyaline membranes rather than the changes described above. Idiopathic bronchiolitis obliterans with organizing pneumonia (BOOP) (choice B) is often a difficult clinical diagnosis to make and may require a lung biopsy which will show connective tissue forming in alveoli and distal bronchioles. Chronic bronchitis (choice C) shows hyperplasia of the bronchial mucous glands and fibrosis of bronchial walls. Emphysema (choice D) is marked by the loss of alveolar walls, leaving large irregular air spaces.

• Question 256:

  A 78-year-old woman is found to have a first morning urine specific gravity of 1.010. Assuming that she has not had anything to drink since yesterday evening, this is most indicative of which of the following?

  A. acute pyelonephritis

  B. advanced renal failure

  C. diabetic glomerulosclerosis

  D. hyperlipidemia

  E. normal kidney function

  Correct Answer: B

  Section: Pathology and Path physiology Aurine specific gravity of 1.010 is the same as the specific gravity of glomerular filtrate (i.e., isosthenuric). Thus, this woman was not concentrating her urine overnight (usual SG > 1.020) which is an indication of severe renal damage as seen in advanced renal failure. Patients with acute pyelonephritis (choice A), diabetic glomerulosclerosis (choice C), and hyperlipidemia (choice D) who are not in advanced renal failure would still be expected to show some overnight concentrating ability as, of course, would normal kidney function (choice E).

• Question 257:

  A 16-year-old boy fractured his leg while running track at school. X-ray studies revealed an abnormality at the lesion site indicating that this was a pathological fracture. Abiopsy of the area was taken and a photomicrograph of the tissue is shown in below figure. The most likely diagnosis is which of the following?

  

  A. chondroblastoma

  B. chondrosarcoma

  C. osteoid osteoma

  D. osteoblastoma

  E. osteochondroma

  F. osteosarcoma

  Correct Answer: F

  Section: Pathology and Path physiology This section in figure shows many large, hyperchromatic, pleomorphic cells that are producing osteoid, typical of an osteosarcoma. A chondroblastoma (choice A) would display sheets of primitive chondroblasts within a cartilage matrix that is irregularly calcified. Chondrosarcoma (choice B) most typically occur in the age range of 4060 with the most common locations being the pelvic girdle, ribs, shoulder girdle, and to a lesser extent the long bones, vertebrae, and sternum. Microscopically, the lower grade tumors will show chondroid differentiation whereas a grade 3 tumor may appear as a spindle cell tumor with little chondroid differentiation. Osteoid osteoma (choice C) and osteoblastoma (choice D) have a very similar microscopic appearance consisting of a random pattern of woven bone with many osteoblasts in evidence within a stroma of granulation-like tissue. Osteoid osteomas are small, very painful tumors that are found in teenagers and young adults and respond very well to aspirin. It usually occurs in the long bones of the leg. Osteoblastomas are larger tumors that more usually affect the vertebrae. Osteochondromas (choice E) (or exostoses) are mushroom-like growths that usually bud from the metaphysic of long bones but may occur, less frequently, at many other sites. Microscopically, one sees irregular trabecular bone covered by a cartilaginous cap.

• Question 258:

  A 59-year-old man complains of periorbital edema and ankle swelling which has been gradually increasing over the past few months. Blood pressure is 120/80 mm Hg. Urinalysis shows a 4+ proteinuria but no cells or casts. Serum albumin is moderately decreased but blood urea nitrogen (BUN) and creatinine are normal. Which of the following is the most likely diagnosis?

  A. acute proliferative glomerulonephritis

  B. diabetic nephropathy

  C. IgA nephropathy

  D. lupus nephritis

  E. membranous glomerulopathy

  Correct Answer: E

  Section: Pathology and Path physiology This patient has nephrotic syndrome as indicated by the edema, 4+ proteinuria, and hypoproteinemia and the most common cause of this syndrome in adults is membranous nephropathy. Acute proliferative glomerulonephritis (choice A) produces a nephritic syndrome marked by a mild proteinuria, hematuria, azotemia, and hypertension. Diabetic nephropathy (choice B) does produce proteinuria that is sometimes sufficient to cause nephrotic syndrome, but hypertension is often present along with some indication of chronic renal failure neither of which are seen in this case. IgA nephropathy or Berger disease (choice C) is a cause of nephrotic syndrome but with hematuria often associated with an upper respiratory infection unlike the presentation in this case. Patients with lupus nephritis (choice D) may present with either nephritic or nephritic syndrome, but certainly this is a much less common cause of nephrotic syndrome than membranous glomerulonephritis.

• Question 259:

  A 66-year-old woman initially develops some subtle changes in memory, judgment, and behavior. However, this is followed by a very severe and rapidly progressive dementia that is accompanied by startle myoclonus. She dies 8 months after the original onset of her symptoms. Her disease is most likely the result of which of the following?

  A. acquired or inherited prion

  B. hereditary lysosomal storage disease

  C. increased neurofibrillary tangles (NFTs)

  D. protozoan infection

  E. repeated exposure to a chemical toxin

  Correct Answer: A

  Section: Pathology and Path physiology Creutzfeldt-Jakob disease is caused by a prion that may either be inherited or acquired during life. Prions are composed of protein only and behave like a slow viral infection. Human prion disease has recently become more prominent with the outbreak of mad cow disease in England due to human consumption of beef tainted with prions. Creutzfeldt- Jakob disease is not known to be inherited as a lysosomal storage disease (choice B) or to be caused by protozoan infections (choice D). Increased NFTs (choice C) are seen with Alzheimer's disease (AD), not Creutzfeldt- Jakob disease. Repeated exposure to chemical toxins (choice E) can cause dementia. Alcohol is a common example. However, the histology of chemical dementia usually differs in character and distribution from the cortical spongiform changes seen in Creutzfeldt-Jakob disease.

• Question 260:

  Molecular studies on a certain carcinoma demonstrate DNA containing multiple sites of adjacent pyrimidine cross-linking to form pyrimidine dimers. This malignancy most likely arose in which of the following sites?

  A. bladder

  B. colon

  C. lung

  D. pancreas

  E. skin

  Correct Answer: E

  Section: Pathology and Path physiology DNApyrimidine dimer formation is a possible carcinogenic consequence induced by the ultraviolet (UV) component of solar radiation. UV radiation comprises three wavelength ranges that are designated UVA, UVB, and UVC. UVB is the principal fraction responsible for the induction of squamous cell carcinoma, basal cell carcinoma, and possibly malignant melanoma of the skin (UVC is also carcinogenic, but is more effectively absorbed by the ozone layer). Aberrant pyrimidine linkages are normally corrected by DNA repair genes (nucleotide excision pathway); however, some errors remain uncorrected if these mechanisms are overwhelmed by excessive sun exposure, potentially leading to transcription errors and oncogenesis. Bladder, colon, lung, and pancreatic cancers (choices AD) frequently arise from mutations in various RAS oncogene proteins, resulting in defective guanine triphosphate (GTP) enzyme activity and increased growth factor signal transduction.