USMLE Step 1 NBME Form 31 Comprehensive Review & Quiz 2026/2027

During autopsy of a 70-year-old man who died in a motor vehicle collision, a small, pedunculated polyp is identified in the transverse colon. Histologic examination shows closely packed tubular glands lined by dysplastic columnar epithelium. Which diagnosis is most likely? A. Hyperplastic polyp B. Tubular adenoma C. Juvenile polyp D. Inflammatory pseudopolyp Correct Answer: B. Tubular adenoma Rationale: A tubular adenoma is a neoplastic polyp composed predominantly of dysplastic tubular glands and carries malignant potential. Hyperplastic polyps contain serrated but nondysplastic glands and generally have little malignant risk. Juvenile polyps contain cystically dilated glands and usually occur in children. Inflammatory pseudopolyps arise from regenerating mucosa in inflammatory bowel disease rather than from neoplastic transformation. Question 2 A 38-year-old man has watery, itchy eyes, sneezing, and rhinorrhea every spring. Examination reveals pale, inflamed nasal mucosa without wheezing or lower respiratory tract findings. Which medication is most appropriate for controlling his symptoms? A. Loratadine B. Albuterol C. Prednisone D. Ipratropium inhalation Correct Answer: A. Loratadine Rationale: Loratadine is a second-generation H1-receptor antagonist that effectively treats allergic rhinitis and allergic conjunctivitis with minimal sedation. Albuterol treats bronchospasm rather than isolated nasal symptoms. Systemic prednisone is unnecessarily potent for uncomplicated seasonal allergies and carries substantial adverse effects. Inhaled ipratropium is primarily used for bronchospasm and does not adequately treat the histamine-mediated itching and sneezing. Question 3 A 16-year-old girl has fever, fatigue, nonproductive cough, and bilateral interstitial pulmonary infiltrates. While her blood specimen awaits laboratory transport, visible agglutination occurs at room temperature. Which antibody isotype most likely caused this finding? A. IgA B. IgE C. IgG D. IgM Correct Answer: D. IgM Rationale: Mycoplasma pneumoniae infection can produce cold agglutinins, which are usually IgM antibodies directed against erythrocyte I antigens. IgM efficiently causes agglutination because its pentameric structure allows extensive cross-linking. IgG is smaller and less efficient at direct agglutination. IgA primarily protects mucosal surfaces, whereas IgE mediates immediate hypersensitivity and defense against parasites. Question 4 A 24-year-old man develops multiple painful, grouped vesicles on an erythematous base over his penis three days after unprotected sexual intercourse. Which infectious agent is the most likely cause? A. Haemophilus ducreyi B. Herpes simplex virus type 2 C. Treponema pallidum D. Human papillomavirus Correct Answer: B. Herpes simplex virus type 2 Rationale: Genital herpes typically produces painful, grouped vesicles that rupture and form shallow ulcers. HSV-2 is the classic cause, although HSV-1 can also produce genital infection. Treponema pallidum causes a painless chancre. Haemophilus ducreyi causes painful, irregular ulcers with associated lymphadenopathy rather than vesicles. Human papillomavirus produces painless verrucous genital warts. Question 5 A 42-year-old woman has recurrent facial erythema involving her cheeks and nose. The condition worsened after she moved to a sunnier climate, and spicy foods trigger flushing. Examination shows telangiectasias and scattered inflammatory papules without comedones. Which diagnosis is most likely? A. Acne vulgaris B. Rosacea C. Seborrheic dermatitis D. Systemic lupus erythematosus Correct Answer: B. Rosacea Rationale: Rosacea causes central facial flushing, persistent erythema, telangiectasias, papules, and pustules. Common triggers include sunlight, heat, alcohol, and spicy foods. Unlike acne vulgaris, rosacea does not produce comedones. Seborrheic dermatitis causes greasy scales, particularly around the scalp and nasolabial folds. Lupus may cause a malar rash but typically spares the nasolabial folds and lacks inflammatory papules. Question 6 A 53-year-old man develops high fever, headache, and abdominal discomfort after returning from sub-Saharan Africa. A Wright-stained peripheral blood smear demonstrates ring-shaped organisms within erythrocytes. Which diagnosis is most likely? A. Babesiosis B. Malaria C. African trypanosomiasis D. Visceral leishmaniasis Correct Answer: B. Malaria Rationale: Malaria is caused by Plasmodium species, which produce intraerythrocytic ring forms visible on peripheral blood smears. Travel to an endemic African region strongly supports the diagnosis. Babesiosis may also produce intraerythrocytic organisms but is associated with tick exposure and occasionally Maltese cross formations. Trypanosomes are extracellular, whereas Leishmania amastigotes are found within macrophages rather than erythrocytes. Question 7 A 68-year-old woman has type 2 diabetes, hypertension, and persistent proteinuria. Her blood pressure remains 150/96 mm Hg despite hydrochlorothiazide therapy. Which medication should be added to slow the progression of her renal disease? A. Amlodipine B. Lisinopril C. Propranolol D. Hydralazine Correct Answer: B. Lisinopril Rationale: Lisinopril, an ACE inhibitor, reduces angiotensin II-mediated efferent arteriolar constriction and decreases intraglomerular pressure. This lowers proteinuria and slows diabetic nephropathy progression. Amlodipine and hydralazine lower systemic blood pressure but provide less direct antiproteinuric protection. Propranolol may control blood pressure but does not offer the same renal protective effect and can mask hypoglycemic symptoms. Question 8 A patient with metastatic colon cancer develops severe diarrhea after receiving irinotecan-based chemotherapy. The physician prescribes an opioid antidiarrheal medication that acts peripherally and has minimal central nervous system effects. Which medication was prescribed? A. Diphenoxylate B. Loperamide C. Morphine D. Naloxone Correct Answer: B. Loperamide Rationale: Loperamide is a peripheral μ-opioid receptor agonist that decreases intestinal motility and increases fluid absorption. It has very limited penetration of the blood-brain barrier and therefore produces minimal analgesia or euphoria. Diphenoxylate can enter the central nervous system and is combined with atropine to discourage abuse. Morphine has substantial central effects, while naloxone is an opioid antagonist. Question 9 A medical volunteer develops profuse “rice-water” diarrhea, severe dehydration, and hypotension after returning from Honduras. Stool microscopy reveals comma-shaped gram-negative organisms without fecal leukocytes. Which cellular mechanism is responsible for the diarrhea? A. Inhibition of adenylate cyclase B. Activation of guanylate cyclase C. Persistent activation of adenylate cyclase D. Destruction of intestinal villi by cytotoxic lymphocytes Correct Answer: C. Persistent activation of adenylate cyclase Rationale: Vibrio cholerae toxin ADP-ribosylates the stimulatory Gs alpha subunit, locking it in an active state. This persistently activates adenylate cyclase, raises intracellular cAMP, and stimulates chloride and water secretion. Heat-stable enterotoxin from enterotoxigenic E. coli activates guanylate cyclase. Villous destruction occurs in disorders such as celiac disease and would cause malabsorption rather than massive secretory diarrhea. Question 10 A 59-year-old woman with metastatic breast cancer develops progressive loss of coordination in her left arm and leg. Strength, sensation, reflexes, and proprioception are normal. Where is the metastatic lesion most likely located? A. Left cerebellar hemisphere B. Right cerebellar hemisphere C. Left internal capsule D. Right dorsal column Correct Answer: A. Left cerebellar hemisphere Rationale: Cerebellar hemisphere lesions produce ipsilateral limb ataxia, dysmetria, and impaired rapid alternating movements. Because the patient’s deficits involve the left arm and leg, the lesion is in the left cerebellar hemisphere. Internal capsule lesions cause contralateral weakness and hyperreflexia. Dorsal column lesions impair proprioception and vibration, which remain normal in this patient.