COMPREHENSIVE MEDICAL
EXAMINATION PRACTICE (USMLE
STEP 1 LEVEL) QUESTIONS AND
ANSWERS
1. A 4-year-old boy presents with intellectual disability, self-mutilation behavior including
biting his lips and fingers, and gouty arthritis. Laboratory results show an elevated serum uric
acid level. Which of the following enzymes is most likely deficient in this patient?
A. Adenosine deaminase
B. Phosphoribosylpyrophosphate synthetase
C. Xanthine oxidase
D. Hypoxanthine-guanine phosphoribosyltransferase
Answer: D
Conceptual Explanation: Lesch-Nyhan syndrome is caused by a deficiency of HGPRT,
leading to an inability to salvage purines, resulting in excess uric acid and neurological
symptoms.
,2. A 65-year-old male smoker presents with a cough and recent weight loss. Chest X-ray
reveals a central lung mass. Laboratory studies show a serum calcium level of 12.5 mg/dL.
Which of the following is the most likely histological diagnosis?
A. Small cell carcinoma
B. Adenocarcinoma
C. Squamous cell carcinoma
D. Large cell carcinoma
Answer: C
Conceptual Explanation: Squamous cell carcinoma is centrally located and frequently
associated with paraneoplastic hypercalcemia due to the production of PTHrP.
3. A 28-year-old woman at 32 weeks gestation presents with sudden onset of severe
abdominal pain and vaginal bleeding. Her blood pressure is 160/100 mmHg. Physical exam
reveals a firm, tender uterus. What is the most likely diagnosis?
A. Placenta previa
B. Uterine rupture
C. Vasa previa
D. Abruptio placentae
Answer: D
, Conceptual Explanation: Abruptio placentae typically presents with painful vaginal
bleeding and a rigid, tender uterus, often associated with hypertension.
4. A patient with a history of chronic alcoholism presents with ataxia, ophthalmoplegia, and
confusion. Which of the following vitamin deficiencies is the most likely cause?
A. Vitamin B6 (Pyridoxine)
B. Vitamin B3 (Niacin)
C. Vitamin B1 (Thiamine)
D. Vitamin B12 (Cobalamin)
Answer: C
Conceptual Explanation: Wernicke encephalopathy presents with the triad of ataxia,
ophthalmoplegia, and confusion, caused by thiamine deficiency.
5. A 45-year-old male is treated for a deep vein thrombosis with heparin. Five days later, his
platelet count drops by 50%. Which of the following is the most likely mechanism of this
condition?
A. Antibodies against platelet factor 4 (PF4) complexed with heparin
B. Direct inhibition of platelet aggregation
C. Splenic sequestration of platelets
D. Bone marrow suppression of megakaryocytes
Answer: A
EXAMINATION PRACTICE (USMLE
STEP 1 LEVEL) QUESTIONS AND
ANSWERS
1. A 4-year-old boy presents with intellectual disability, self-mutilation behavior including
biting his lips and fingers, and gouty arthritis. Laboratory results show an elevated serum uric
acid level. Which of the following enzymes is most likely deficient in this patient?
A. Adenosine deaminase
B. Phosphoribosylpyrophosphate synthetase
C. Xanthine oxidase
D. Hypoxanthine-guanine phosphoribosyltransferase
Answer: D
Conceptual Explanation: Lesch-Nyhan syndrome is caused by a deficiency of HGPRT,
leading to an inability to salvage purines, resulting in excess uric acid and neurological
symptoms.
,2. A 65-year-old male smoker presents with a cough and recent weight loss. Chest X-ray
reveals a central lung mass. Laboratory studies show a serum calcium level of 12.5 mg/dL.
Which of the following is the most likely histological diagnosis?
A. Small cell carcinoma
B. Adenocarcinoma
C. Squamous cell carcinoma
D. Large cell carcinoma
Answer: C
Conceptual Explanation: Squamous cell carcinoma is centrally located and frequently
associated with paraneoplastic hypercalcemia due to the production of PTHrP.
3. A 28-year-old woman at 32 weeks gestation presents with sudden onset of severe
abdominal pain and vaginal bleeding. Her blood pressure is 160/100 mmHg. Physical exam
reveals a firm, tender uterus. What is the most likely diagnosis?
A. Placenta previa
B. Uterine rupture
C. Vasa previa
D. Abruptio placentae
Answer: D
, Conceptual Explanation: Abruptio placentae typically presents with painful vaginal
bleeding and a rigid, tender uterus, often associated with hypertension.
4. A patient with a history of chronic alcoholism presents with ataxia, ophthalmoplegia, and
confusion. Which of the following vitamin deficiencies is the most likely cause?
A. Vitamin B6 (Pyridoxine)
B. Vitamin B3 (Niacin)
C. Vitamin B1 (Thiamine)
D. Vitamin B12 (Cobalamin)
Answer: C
Conceptual Explanation: Wernicke encephalopathy presents with the triad of ataxia,
ophthalmoplegia, and confusion, caused by thiamine deficiency.
5. A 45-year-old male is treated for a deep vein thrombosis with heparin. Five days later, his
platelet count drops by 50%. Which of the following is the most likely mechanism of this
condition?
A. Antibodies against platelet factor 4 (PF4) complexed with heparin
B. Direct inhibition of platelet aggregation
C. Splenic sequestration of platelets
D. Bone marrow suppression of megakaryocytes
Answer: A
