USMLE USMLE Certifications USMLE Questions & Answers

• Question 431:

  A group of research scientists are studying immunohistochemical stains used for detecting the different types of cell. The stain which is used to detect epithelial cells is:

  A. chromogranin

  B. cytokeratin

  C. desmin

  D. neurofilaments

  E. vimentin

  Correct Answer: B

  Explanation:

  Cytokeratin is a keratin-containing intermediate filament found in the intracytoplasmic cytoskeleton of epithelial tissue. In the cytoplasm, the keratin filaments form a complex network which extends from the surface of the nucleus to the cell membrane. The cytokeratin stain is used to detect epithelial cells and tumors.

• Question 432:

  A 2-year-old male is brought to the physician due to mental retardation. Physical examination reveals a single palmar crease, flat face and prominent epicanthal folds. The most likely cause of these findings is:

  A. heteroplasmy

  B. incomplete penetrance

  C. meiotic nondisjunction

  D. mosaicism

  E. Robertsonian translocation

  Correct Answer: C

  Explanation:

  This patient with a flat face, mental retardation, prominent epicanthal folds and a single palmar crease most likely has trisomy 21 also called Down syndrome. It is the most common cause of genetic intellectual disability. Other findings in patients with trisomy 21 include duodenal atresia, Hirsch sprung disease, atrioventricular septal defects, Brush field spots and early onset Alzheimer disease. The most common cause of Down syndrome is meiotic nondisjunction in older pregnant females. A few cases of Down syndrome are caused by unbalanced Robertsonian translocations mostly between chromosomes 14 and 21 and only 1% of cases are due to post-fertilization mitotic errors. Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division. Meiotic nondisjunction is implicated in 95% of Down syndrome cases.

• Question 433:

  A 40-year-old male comes to the emergency department due to a two-week history of a productive cough

  that is occasionally associated with blood. He has had similar episodes in the past. Vitals reveal a blood

  pressure of 140/80 mmHg, a heart rate of 75/min, a temperature of 37.6°C (99 6°F) and a respiratory rate

  of 16/min. Oxygen saturation is 90% on room air. Laboratory results are as follows:

  Complete blood count

  Hemoglobin 11.8 g/dL

  Hematocrit 35.4%

  Mean Corpuscular Volume 85 µm³

  Leukocytes10,000/mm³

  Differential: Neutrophils 60%

  Bands 3%

  Lymphocytes 25%

  Monocytes 7%

  Eosinophils 3%,

  Liver function studies

  Alanine aminotransferase – 15 U/L

  Aspartate aminotransferase – 90 U/L

  Serum chemistry Creatinine – 1.5 mg/dL

  Blood urea nitrogen – 23 mg/dL

  Urinalysis2+ blood, red blood cell casts.

  The most likely other finding in this patient's serum is

  A. anti-basement membrane antibodies

  B. anti-double stranded DNA antibodies

  C. anti-mitochondrial antibodies

  D. anti-myeloperoxidase antibodies

  E. anti-proteinase 3 antibodies

  Correct Answer: A

  Explanation:

  This patient most likely has Good pasture syndrome which is a type of rapidly progressive glomerulonephritis characterized by the presence of autoantibodies to the glomerular and alveolar basement membranes. It usually presents with hemoptysis, glomerulonephritis and hematuria. Good pasture syndrome is an example of a type II cytotoxic hypersensitivity reaction. Laboratory findings include a linear pattern of IgG deposition within glomeruli on fluorescent antibody testing. Treatment is with plasmapheresis.

• Question 434:

  A 45-year-old female comes to the physician because of headaches and palpitations. Vitals reveal a blood pressure of 190/140 mm Hg and a heart rate of 105/min. A CT scan of the abdomen is obtained which reveals an adrenal mass. The hormones secreted by the adrenal mass are derived from:

  A. arginine

  B. glutamate

  C. glycine

  D. tryptophan

  E. tyrosine

  Correct Answer: E

  Explanation:

  This patient has an adrenal pheochromocytoma which is the most common adrenal medullar tumor in adults. It usually presents with episodic hypertension, headaches and palpitations. The tumor arises from the sympathetic chromaffin cells in the adrenal gland hence it secretes catecholamines such as epinephrine, norepinephrine and dopamine which are derived from tyrosine.

• Question 435:

  A 3-year-old male is brought to the physician due to an enlarging abdominal mass. Physical examination reveals a mass in the left abdomen that does not cross the midline. Ophthalmic examination is unremarkable. Microscopic examination of a biopsy specimen from the abdomen reveals dense immature islands of epithelial cells, ribbons of spindle fibroblastic stromal cells and poorly formed tubular structures. The most likely diagnosis:

  A. embryonal rhabdomyosarcoma

  B. Ewing sarcoma

  C. Hodgkin disease

  D. neuroblastoma

  E. Wilms tumor

  Correct Answer: E

  Explanation: Wilms tumor is the most common renal malignancy of early childhood (ages 2–4) that can present as an abdominal mass with hypertension, nausea, hematuria, and intestinal obstruction. Histologically, it is a neoplasm of the embryonic renal tissue that consists of both neoplastic epithelia and a stromal component. It is associated with mutations of the tumor suppressor genes WT1 or WT2 on chromosome 11. A close differential diagnosis for this child is a neuroblastoma but it is an extrarenal tumor which crosses the midline. Wilms tumor may also be associated with several syndromes such as the aniridia, genitourinary malformations and mental/motor retardation syndrome (WAGR complex), Denys-Drash syndrome and Beckwith-Wiedemann syndrome.

• Question 436:

  A 60-year-old male with a past medical history of hyperlipidemia and hepatic dysfunction comes to the physician for a routine examination. He states that he has had difficulty initiating urination for the past seven months with an intermittent urine stream and urinary urgency. Vitals reveal a blood pressure of 150/90 mmHg,a heart rate of 65/min, a temperature of 37.0°C (98.6°F) and a respiratory rate of 12/min. Digital rectal examination reveals diffuse enlargement of the prostate. The most appropriate pharmacologic treatment for this patient is most likely a drug that:

  A. activates central alpha-2 receptors

  B. blocks alpha and beta receptors

  C. blocks muscarinic receptors

  D. inhibits 5-alpha reductase

  E. selectively blocks alpha-1 receptors

  Correct Answer: E

  Explanation:

  This patient has the clinical findings consistent with benign prostatic hyperplasia (BPH). He also seems to have hypertension. BPH usually presents with difficulty initiating urination, a decreased urinary stream, nocturia, high postvoid residual volume and urinary retention. High concentrations of alpha-1-adrenergic receptors are found in the smooth muscle of the bladder neck and stroma and capsule of the prostate. Stimulation of these receptors causes increased smooth muscle tone and blockade of these receptors can reversibly relax these muscles, leading to decreased urinary symptoms. Terazosin and doxazosin are examples of alpha-l-adrenergic antagonists that act in vascular smooth muscle, producing relaxation and relief of urinary symptoms. They are indicated for the treatment of both BPH and hypertension (vascular smooth muscle).

• Question 437:

  A 50-year-old male is brought to the emergency department due to an acute onset chest pain that radiates to his jaw. An ECG reveals ST segment elevation in leads II, III and a VF. He undergoes percutaneous coronary intervention with stenting without any complications. The patient is discharged from the hospital three days later with aspirin and clopidogrel. He returns to the emergency department eight weeks later due to recurrent chest pain which he describes as a sharp pain that worsens when he lies flat. The pain does not radiate or improve with nitroglycerin tablets. Vitals reveal a blood pressure of 135/87 mmHg, a heart rate of 84/min, a temperature of 38.0°C (100.5°F) and a respiratory rate of 12/min. Oxygen saturation is 98% on room air. Physical examination reveals a harsh three component extra heart sound heard best at the left lower sternal border. An ECG is obtained which reveals diffuse ST elevations. The most likely cause of the current findings is

  A. autoimmune pericarditis

  B. infective endocarditis

  C. papillary muscle rupture

  D. prinzmetal angina

  E. stent thrombosis

  Correct Answer: A

  Explanation:

  This patient most likely has Dressler syndrome, which is an autoimmune post-myocardial infarction phenomenon resulting in fibrinous pericarditis. Fibrinous pericarditis presents with fever and positional chest pain, with patients generally preferring to remain upright and leaning forward. Physical examination findings include a loud three component pericardial friction rub heard on auscultation and ECG changes include diffuse ST segment elevations. Patients with autoimmune pericarditis typically present several weeks after an acute myocardial infarction.

• Question 438:

  An 18-month-old male is brought to the physician due to mental retardation and abdominal distention. Physical examination reveals enlargement of the liver and spleen. Fundoscopy reveals a cherry red spot on the macula. The most likely other finding in this patient is increased levels of

  A. ceramide trihexoside

  B. cerebroside sulfate

  C. galactocerebroside

  D. GM2 ganglioside

  E. sphingomyelin

  Correct Answer: E

  Explanation:

  This patient most likely has Niemann-Pick disease which is an autosomal recessive lysosomal storage disease caused by a deficiency of sphingomyelinase. Itis more common is Ashkenazi Jews. Deficiency of sphingomyelinase leads to the accumulation of sphingomyelin, progressive neurodegeneration, hepatosplenomegaly and lipid laden macrophages also called foam cells. Similar to Tay-Sachs disease, a “cherry-red” spot can be seen on the macula.

• Question 439:

  A 34-year-old female comes to the physician with nausea and abdominal pain. She indicates that the pain is epigastric, and it improves with food intake. She also reports recent weight gain. A urease breath test is obtained which is positive. This patient is most likely at an increased risk for developing

  A. bladder cancer

  B. brain abscesses

  C. gastric adenocarcinoma

  D. heart block

  E. myocarditis

  Correct Answer: C

  Explanation:

  This patient most likely has a duodenal ulcer caused by infection with Helicobacter pylori. Helicobacter pylori is a urease positive, catalase positive, oxidase positive, curved shaped gram-negative bacterium. It may colonize the antrum of the stomach and cause gastric ulcers or colonize the first part of the duodenum causing duodenal ulcers. Infection with H. pylori increases the risk for developing peptic ulcer disease, gastric adenocarcinomas and MALT lymphomas.

• Question 440:

  A 27-year-old male comes to the physician with skin lesions as shown in the exhibit. Physical examination reveals soft tissue crepitus and the smell of decomposing tissue. The most likely cause of these findings can also cause infection through

  A. ingestion

  B. fecal-oral transmission

  C. respiratory droplet inhalation

  D. sexual transmission

  E. skin to skin transmission

  Correct Answer: A

  Explanation:

  This patient's clinical findings are consistent with gas gangrene and myonecrosis caused by an infection with the gram-positive bacteria Clostridium perfringens. The myonecrosis which causes gas gangrene heard as crepitus in the soft tissues is caused by the bacterium's alpha toxin which functions as a phospholipase. The route of infection resulting in myonecrosis is infection of an open skin wound by the soil-borne anaerobic bacteria. The spores of C. perfringens can also survive in undercooked food and when ingested, cause food poisoning. To answer this question correctly, you first have to make the diagnosis, know the cause of the diagnosis, the other type of illness it causes and its route of infection.