USMLE STEP 1 STYLE PRACTICE EXAM WITH 60 HIGH-YIELD QUESTIONS. EACH
QUESTION HAS THE CORRECT ANSWER IN BOLD AND THE RATIONALE IN ITALICS.
Question 1
A 45-year-old man with chronic alcoholism presents with confusion, ataxia, and
ophthalmoplegia. Which vitamin deficiency is most likely responsible?
A) Vitamin A
B) Vitamin B12
C) Thiamine (Vitamin B1)
D) Vitamin C
E) Vitamin D
Rationale: The triad of confusion, ataxia, and ophthalmoplegia is classic for
Wernicke encephalopathy, caused by thiamine (B1) deficiency, often seen in
chronic alcoholism.
Question 2
A 30-year-old woman develops hemolytic anemia after starting an antibiotic.
Laboratory studies show low haptoglobin, elevated LDH, and a positive direct
antiglobulin test (Coombs test). Which type of hypersensitivity reaction is this?
A) Type I
B) Type II
C) Type III
D) Type IV
E) Type V
Rationale: Type II hypersensitivity involves antibody-mediated destruction of cells
(IgG/IgM against RBCs) → positive direct Coombs test. Drug-induced hemolytic
anemia is a classic example.
,Question 3
A 60-year-old man with hypertension is on a thiazide diuretic. Which electrolyte
abnormality is most commonly associated with this medication?
A) Hypernatremia
B) Hyperkalemia
C) Hypokalemia
D) Hypercalcemia
E) Hypomagnesemia
Rationale: Thiazide diuretics increase sodium delivery to the distal tubule,
promoting potassium excretion, leading to hypokalemia. They also cause
hypomagnesemia but less consistently; hypokalemia is the classic finding.
Question 4
A biopsy of a mediastinal mass shows CD15+, CD30+ Reed–Sternberg cells with
abundant reactive lymphocytes. What is the most likely diagnosis?
A) Burkitt lymphoma
B) Diffuse large B-cell lymphoma
C) Hodgkin lymphoma, nodular sclerosis type
D) Small lymphocytic lymphoma
E) Mantle cell lymphoma
*Rationale: CD15+, CD30+ Reed–Sternberg cells in a background of reactive cells
are diagnostic of classical Hodgkin lymphoma. Nodular sclerosis is the most
common subtype, often presenting as a mediastinal mass.*
Question 5
A 25-year-old medical student experiences palpitations and sweating while
drinking coffee. Caffeine antagonizes which receptor?
, A) Nicotinic acetylcholine receptor
B) Adenosine A1 and A2A receptors
C) Dopamine D2 receptor
D) GABAA receptor
E) β1-adrenergic receptor
Rationale: Caffeine is a nonselective antagonist of adenosine receptors (A1 and
A2A). Blocking these receptors increases arousal and sympathetic activity, leading
to palpitations and sweating.
Question 6
A patient has a defect in the enzyme branched-chain alpha-keto acid
dehydrogenase. Which amino acids will accumulate?
A) Phenylalanine, tyrosine, tryptophan
B) Leucine, isoleucine, valine
C) Methionine, threonine, lysine
D) Alanine, glycine, serine
E) Arginine, ornithine, citrulline
Rationale: Deficiency of branched-chain alpha-keto acid dehydrogenase causes
maple syrup urine disease, with accumulation of leucine, isoleucine, and valine.
Question 7
A 55-year-old woman with breast cancer treated with doxorubicin develops
dyspnea and peripheral edema. Echocardiography shows dilated cardiomyopathy.
What is the mechanism of doxorubicin cardiotoxicity?
A) Microtubule stabilization
B) Free radical generation and topoisomerase II inhibition
C) Mitochondrial DNA intercalation
QUESTION HAS THE CORRECT ANSWER IN BOLD AND THE RATIONALE IN ITALICS.
Question 1
A 45-year-old man with chronic alcoholism presents with confusion, ataxia, and
ophthalmoplegia. Which vitamin deficiency is most likely responsible?
A) Vitamin A
B) Vitamin B12
C) Thiamine (Vitamin B1)
D) Vitamin C
E) Vitamin D
Rationale: The triad of confusion, ataxia, and ophthalmoplegia is classic for
Wernicke encephalopathy, caused by thiamine (B1) deficiency, often seen in
chronic alcoholism.
Question 2
A 30-year-old woman develops hemolytic anemia after starting an antibiotic.
Laboratory studies show low haptoglobin, elevated LDH, and a positive direct
antiglobulin test (Coombs test). Which type of hypersensitivity reaction is this?
A) Type I
B) Type II
C) Type III
D) Type IV
E) Type V
Rationale: Type II hypersensitivity involves antibody-mediated destruction of cells
(IgG/IgM against RBCs) → positive direct Coombs test. Drug-induced hemolytic
anemia is a classic example.
,Question 3
A 60-year-old man with hypertension is on a thiazide diuretic. Which electrolyte
abnormality is most commonly associated with this medication?
A) Hypernatremia
B) Hyperkalemia
C) Hypokalemia
D) Hypercalcemia
E) Hypomagnesemia
Rationale: Thiazide diuretics increase sodium delivery to the distal tubule,
promoting potassium excretion, leading to hypokalemia. They also cause
hypomagnesemia but less consistently; hypokalemia is the classic finding.
Question 4
A biopsy of a mediastinal mass shows CD15+, CD30+ Reed–Sternberg cells with
abundant reactive lymphocytes. What is the most likely diagnosis?
A) Burkitt lymphoma
B) Diffuse large B-cell lymphoma
C) Hodgkin lymphoma, nodular sclerosis type
D) Small lymphocytic lymphoma
E) Mantle cell lymphoma
*Rationale: CD15+, CD30+ Reed–Sternberg cells in a background of reactive cells
are diagnostic of classical Hodgkin lymphoma. Nodular sclerosis is the most
common subtype, often presenting as a mediastinal mass.*
Question 5
A 25-year-old medical student experiences palpitations and sweating while
drinking coffee. Caffeine antagonizes which receptor?
, A) Nicotinic acetylcholine receptor
B) Adenosine A1 and A2A receptors
C) Dopamine D2 receptor
D) GABAA receptor
E) β1-adrenergic receptor
Rationale: Caffeine is a nonselective antagonist of adenosine receptors (A1 and
A2A). Blocking these receptors increases arousal and sympathetic activity, leading
to palpitations and sweating.
Question 6
A patient has a defect in the enzyme branched-chain alpha-keto acid
dehydrogenase. Which amino acids will accumulate?
A) Phenylalanine, tyrosine, tryptophan
B) Leucine, isoleucine, valine
C) Methionine, threonine, lysine
D) Alanine, glycine, serine
E) Arginine, ornithine, citrulline
Rationale: Deficiency of branched-chain alpha-keto acid dehydrogenase causes
maple syrup urine disease, with accumulation of leucine, isoleucine, and valine.
Question 7
A 55-year-old woman with breast cancer treated with doxorubicin develops
dyspnea and peripheral edema. Echocardiography shows dilated cardiomyopathy.
What is the mechanism of doxorubicin cardiotoxicity?
A) Microtubule stabilization
B) Free radical generation and topoisomerase II inhibition
C) Mitochondrial DNA intercalation
