NBME CBSE AND USMLE STEP 1
COMPREHENSIVE QUESTIONS AND
ANSWERS
1. A 45-year-old male presents with a sudden onset of excruciating pain in his right first
metatarsophalangeal joint. Microscopic examination of joint aspirate reveals needle-shaped
crystals with negative birefringence. Which of the following is the most likely diagnosis?
A. Pseudogout
B. Rheumatoid arthritis
C. Gout
D. Septic arthritis
Answer: C
Conceptual Explanation: Gout is characterized by monosodium urate crystals that are
needle-shaped and negatively birefringent under polarized light.
2. A 24-year-old woman presents with polyuria and polydipsia. Her fasting blood glucose is
110 mg/dL. A water deprivation test is performed; her urine osmolality remains low but
increases significantly after administration of desmopressin. What is the most likely
diagnosis?
A. Primary polydipsia
,B. Central diabetes insipidus
C. Nephrogenic diabetes insipidus
D. Syndrome of inappropriate ADH
Answer: B
Conceptual Explanation: In central diabetes insipidus, there is a deficiency of ADH. The
kidneys respond to exogenous ADH (desmopressin) by increasing urine osmolality.
3. Which of the following biochemical pathways is primarily affected in a patient with a
deficiency of glucose-6-phosphate dehydrogenase (G6PD)?
A. Pentose phosphate pathway
B. Gluconeogenesis
C. Glycolysis
D. Citric acid cycle
Answer: A
Conceptual Explanation: G6PD is the rate-limiting enzyme of the pentose phosphate
pathway, which is essential for maintaining reduced glutathione levels to protect cells from
oxidative stress.
, 4. A 60-year-old smoker presents with a cough and weight loss. Imaging shows a central lung
mass. Laboratory results reveal hyponatremia. Which lung cancer type is most likely
responsible for this presentation?
A. Small cell lung carcinoma
B. Large cell carcinoma
C. Squamous cell carcinoma
D. Adenocarcinoma
Answer: A
Conceptual Explanation: Small cell lung carcinoma is often central and frequently
associated with paraneoplastic syndromes like SIADH, causing hyponatremia.
5. A 55-year-old male with a history of atrial fibrillation is started on warfarin. Which of the
following laboratory values must be monitored to ensure therapeutic efficacy and safety?
A. Partial thromboplastin time (PTT)
B. Prothrombin time (PT) / INR
C. Bleeding time
D. Platelet count
Answer: B
Conceptual Explanation: Warfarin inhibits vitamin K epoxide reductase, affecting factors
II, VII, IX, and X. The extrinsic pathway and PT/INR are used for monitoring.
COMPREHENSIVE QUESTIONS AND
ANSWERS
1. A 45-year-old male presents with a sudden onset of excruciating pain in his right first
metatarsophalangeal joint. Microscopic examination of joint aspirate reveals needle-shaped
crystals with negative birefringence. Which of the following is the most likely diagnosis?
A. Pseudogout
B. Rheumatoid arthritis
C. Gout
D. Septic arthritis
Answer: C
Conceptual Explanation: Gout is characterized by monosodium urate crystals that are
needle-shaped and negatively birefringent under polarized light.
2. A 24-year-old woman presents with polyuria and polydipsia. Her fasting blood glucose is
110 mg/dL. A water deprivation test is performed; her urine osmolality remains low but
increases significantly after administration of desmopressin. What is the most likely
diagnosis?
A. Primary polydipsia
,B. Central diabetes insipidus
C. Nephrogenic diabetes insipidus
D. Syndrome of inappropriate ADH
Answer: B
Conceptual Explanation: In central diabetes insipidus, there is a deficiency of ADH. The
kidneys respond to exogenous ADH (desmopressin) by increasing urine osmolality.
3. Which of the following biochemical pathways is primarily affected in a patient with a
deficiency of glucose-6-phosphate dehydrogenase (G6PD)?
A. Pentose phosphate pathway
B. Gluconeogenesis
C. Glycolysis
D. Citric acid cycle
Answer: A
Conceptual Explanation: G6PD is the rate-limiting enzyme of the pentose phosphate
pathway, which is essential for maintaining reduced glutathione levels to protect cells from
oxidative stress.
, 4. A 60-year-old smoker presents with a cough and weight loss. Imaging shows a central lung
mass. Laboratory results reveal hyponatremia. Which lung cancer type is most likely
responsible for this presentation?
A. Small cell lung carcinoma
B. Large cell carcinoma
C. Squamous cell carcinoma
D. Adenocarcinoma
Answer: A
Conceptual Explanation: Small cell lung carcinoma is often central and frequently
associated with paraneoplastic syndromes like SIADH, causing hyponatremia.
5. A 55-year-old male with a history of atrial fibrillation is started on warfarin. Which of the
following laboratory values must be monitored to ensure therapeutic efficacy and safety?
A. Partial thromboplastin time (PTT)
B. Prothrombin time (PT) / INR
C. Bleeding time
D. Platelet count
Answer: B
Conceptual Explanation: Warfarin inhibits vitamin K epoxide reductase, affecting factors
II, VII, IX, and X. The extrinsic pathway and PT/INR are used for monitoring.
