NBME CBSE EXAM 300 ACTUAL QUESTIONS AND
CORRECT ANSWERS WITH RATIONALE LATEST
UPDATE ALREADY GRADED A+ ASSURED PASS
This comprehensive 300-question bank mirrors the NBME CBSE blueprint,
covering high-yield pathology, pharmacology, physiology, and clinical reasoning.
Each unique question presents a clinical vignette followed by five multiple-choice
options, a single correct answer, and a detailed rationale explaining the underlying
mechanism, differential diagnosis, or management principle. The content spans
major organ systems—cardiovascular, pulmonary, renal, gastrointestinal,
neurologic, and endocrine—along with oncology, immunology, and infectious
disease. Questions emphasize board-relevant associations, classic presentations,
diagnostic workups, and therapeutic interventions, making this an effective self-
assessment tool for reinforcing foundational science knowledge and predicting
USMLE Step 1 readiness.
Question 1
A 45-year-old male presents with fatigue, weight loss, and a persistent cough.
Chest X-ray reveals a hilar mass and mediastinal lymphadenopathy. A biopsy
shows a tumor composed of large cells with prominent nucleoli and a "fried egg"
appearance. Which immunohistochemical marker is most likely positive in this
neoplasm?
A) Cytokeratin
B) CD20
C) CD3
D) S100
E) CD15
Answer: E) CD15
Rationale: The clinical and histologic description is classic for Hodgkin
lymphoma, specifically the nodular sclerosis subtype. The hallmark Reed-
Sternberg cells are large, have prominent nucleoli, and appear like "fried eggs" or
"owl eyes." These cells characteristically express CD15 and CD30, while being
negative for leukocyte common antigen (CD45) and B-cell markers like CD20.
,Cytokeratin is for epithelial tumors, CD20 for B-cell lymphomas, CD3 for T-cells,
and S100 for melanocytic or neural tumors.
---
Question 2
A 28-year-old woman with a history of systemic lupus erythematosus presents with
acute onset of shortness of breath and pleuritic chest pain. She is found to have a
pulmonary embolism. Laboratory studies show a prolonged partial thromboplastin
time (PTT) that does not correct with mixing studies. Which antibody is most
likely responsible for this laboratory finding?
A) Anti-dsDNA
B) Anti-Smith
C) Anti-Ro/SSA
D) Anti-cardiolipin
E) Anti-histone
Answer: D) Anti-cardiolipin
Rationale: The scenario describes a patient with SLE who has a thrombotic event
(pulmonary embolism) and a prolonged PTT that does not correct on mixing,
indicating the presence of a lupus anticoagulant. This antibody is directed against
phospholipid-protein complexes and is detected clinically as anti-cardiolipin or
anti-beta2-glycoprotein I antibodies. It paradoxically causes thrombosis despite
prolonging the PTT in vitro. Anti-dsDNA and anti-Smith are specific for SLE but
are not associated with this coagulation finding. Anti-Ro is linked to neonatal lupus
and Sjogren syndrome, while anti-histone is seen in drug-induced lupus.
---
Question 3
A 60-year-old man with a 30-pack-year smoking history presents with hemoptysis
and weight loss. CT scan shows a central lung mass. Bronchoscopy reveals a tumor
obstructing the right main bronchus. Biopsy shows small cells with scant
cytoplasm, nuclear molding, and salt-and-pepper chromatin. Which paraneoplastic
syndrome is most commonly associated with this tumor type?
A) Hypercalcemia
B) Syndrome of inappropriate antidiuretic hormone (SIADH)
C) Hypertrophic pulmonary osteoarthropathy
D) Gynecomastia
E) Carcinoid syndrome
,Answer: B) Syndrome of inappropriate antidiuretic hormone (SIADH)
Rationale: The histologic description is classic for small cell lung carcinoma
(SCLC), a neuroendocrine tumor that arises centrally and is strongly associated
with smoking. SCLC is notorious for producing ectopic hormones, most
commonly antidiuretic hormone (ADH), leading to SIADH with hyponatremia and
euvolemic hypo-osmolality. Hypercalcemia is more typical of squamous cell
carcinoma due to parathyroid hormone-related peptide (PTHrP). Hypertrophic
pulmonary osteoarthropathy is seen with non-small cell lung cancers, particularly
adenocarcinoma. Gynecomastia can be seen with human chorionic gonadotropin
(hCG) secretion from large cell carcinoma, and carcinoid syndrome occurs with
carcinoid tumors, typically in the GI tract or bronchus, but is less common than
SIADH in SCLC.
---
Question 4
A 32-year-old woman presents with episodic palpitations, diaphoresis, and severe
headaches. She is found to have hypertension that is poorly controlled on multiple
medications. A 24-hour urine collection shows elevated metanephrines. Which of
the following genetic syndromes is most strongly associated with this condition?
A) Neurofibromatosis type 1
B) Multiple endocrine neoplasia type 2A
C) Von Hippel-Lindau disease
D) Tuberous sclerosis
E) Li-Fraumeni syndrome
Answer: B) Multiple endocrine neoplasia type 2A
Rationale: The clinical presentation of episodic hypertension, palpitations,
diaphoresis, and headaches, along with elevated urinary metanephrines, is
diagnostic for pheochromocytoma, a catecholamine-secreting tumor of the adrenal
medulla. Pheochromocytoma is a hallmark feature of MEN 2A, which also
includes medullary thyroid carcinoma and primary hyperparathyroidism, all due to
a germline mutation in the RET proto-oncogene. Neurofibromatosis type 1 and
Von Hippel-Lindau disease are also associated with pheochromocytoma but are
less strongly linked than MEN 2A in the classic triad. Tuberous sclerosis causes
hamartomas and angiofibromas, not pheochromocytoma, and Li-Fraumeni is
associated with sarcomas and early-onset breast cancer.
---
, Question 5
A 55-year-old male with a history of hepatitis C presents with ascites, jaundice,
and confusion. On physical exam, he has spider angiomas and palmar erythema.
Laboratory studies show elevated ammonia. Which of the following is the primary
mechanism of hepatic encephalopathy in this patient?
A) Accumulation of gamma-aminobutyric acid (GABA)
B) Increased cerebral uptake of aromatic amino acids
C) Direct hepatocyte injury from ammonia
D) Decreased clearance of ammonia by the liver leading to astrocyte swelling
E) Portosystemic shunting of insulin
Answer: D) Decreased clearance of ammonia by the liver leading to astrocyte
swelling
Rationale: In chronic liver disease, such as that from hepatitis C, impaired hepatic
function and portosystemic shunting lead to increased systemic ammonia.
Ammonia crosses the blood-brain barrier and is taken up by astrocytes, where it is
converted to glutamine. The accumulation of glutamine increases intracellular
osmotic pressure, causing astrocyte swelling and cerebral edema, which
contributes to the altered mental status seen in hepatic encephalopathy. GABA
accumulation is a secondary effect, not the primary mechanism. Aromatic amino
acids increase but this is related to altered neurotransmitter balance, not the direct
cause. Hepatocyte injury from ammonia is not the mechanism, and insulin shunting
is not directly implicated in encephalopathy.
---
Question 6
A 7-year-old child presents with recurrent respiratory infections and failure to
thrive. Sweat chloride testing is positive. Genetic testing reveals a mutation in the
CFTR gene. Which of the following cellular mechanisms is primarily disrupted in
this condition?
A) Defective sodium reabsorption in the renal tubules
B) Impaired chloride secretion and increased sodium absorption in epithelial cells
C) Decreased mucus production in the lungs
D) Enhanced bicarbonate secretion in the pancreas
E) Defective ciliary movement in the respiratory tract
Answer: B) Impaired chloride secretion and increased sodium absorption in
epithelial cells
CORRECT ANSWERS WITH RATIONALE LATEST
UPDATE ALREADY GRADED A+ ASSURED PASS
This comprehensive 300-question bank mirrors the NBME CBSE blueprint,
covering high-yield pathology, pharmacology, physiology, and clinical reasoning.
Each unique question presents a clinical vignette followed by five multiple-choice
options, a single correct answer, and a detailed rationale explaining the underlying
mechanism, differential diagnosis, or management principle. The content spans
major organ systems—cardiovascular, pulmonary, renal, gastrointestinal,
neurologic, and endocrine—along with oncology, immunology, and infectious
disease. Questions emphasize board-relevant associations, classic presentations,
diagnostic workups, and therapeutic interventions, making this an effective self-
assessment tool for reinforcing foundational science knowledge and predicting
USMLE Step 1 readiness.
Question 1
A 45-year-old male presents with fatigue, weight loss, and a persistent cough.
Chest X-ray reveals a hilar mass and mediastinal lymphadenopathy. A biopsy
shows a tumor composed of large cells with prominent nucleoli and a "fried egg"
appearance. Which immunohistochemical marker is most likely positive in this
neoplasm?
A) Cytokeratin
B) CD20
C) CD3
D) S100
E) CD15
Answer: E) CD15
Rationale: The clinical and histologic description is classic for Hodgkin
lymphoma, specifically the nodular sclerosis subtype. The hallmark Reed-
Sternberg cells are large, have prominent nucleoli, and appear like "fried eggs" or
"owl eyes." These cells characteristically express CD15 and CD30, while being
negative for leukocyte common antigen (CD45) and B-cell markers like CD20.
,Cytokeratin is for epithelial tumors, CD20 for B-cell lymphomas, CD3 for T-cells,
and S100 for melanocytic or neural tumors.
---
Question 2
A 28-year-old woman with a history of systemic lupus erythematosus presents with
acute onset of shortness of breath and pleuritic chest pain. She is found to have a
pulmonary embolism. Laboratory studies show a prolonged partial thromboplastin
time (PTT) that does not correct with mixing studies. Which antibody is most
likely responsible for this laboratory finding?
A) Anti-dsDNA
B) Anti-Smith
C) Anti-Ro/SSA
D) Anti-cardiolipin
E) Anti-histone
Answer: D) Anti-cardiolipin
Rationale: The scenario describes a patient with SLE who has a thrombotic event
(pulmonary embolism) and a prolonged PTT that does not correct on mixing,
indicating the presence of a lupus anticoagulant. This antibody is directed against
phospholipid-protein complexes and is detected clinically as anti-cardiolipin or
anti-beta2-glycoprotein I antibodies. It paradoxically causes thrombosis despite
prolonging the PTT in vitro. Anti-dsDNA and anti-Smith are specific for SLE but
are not associated with this coagulation finding. Anti-Ro is linked to neonatal lupus
and Sjogren syndrome, while anti-histone is seen in drug-induced lupus.
---
Question 3
A 60-year-old man with a 30-pack-year smoking history presents with hemoptysis
and weight loss. CT scan shows a central lung mass. Bronchoscopy reveals a tumor
obstructing the right main bronchus. Biopsy shows small cells with scant
cytoplasm, nuclear molding, and salt-and-pepper chromatin. Which paraneoplastic
syndrome is most commonly associated with this tumor type?
A) Hypercalcemia
B) Syndrome of inappropriate antidiuretic hormone (SIADH)
C) Hypertrophic pulmonary osteoarthropathy
D) Gynecomastia
E) Carcinoid syndrome
,Answer: B) Syndrome of inappropriate antidiuretic hormone (SIADH)
Rationale: The histologic description is classic for small cell lung carcinoma
(SCLC), a neuroendocrine tumor that arises centrally and is strongly associated
with smoking. SCLC is notorious for producing ectopic hormones, most
commonly antidiuretic hormone (ADH), leading to SIADH with hyponatremia and
euvolemic hypo-osmolality. Hypercalcemia is more typical of squamous cell
carcinoma due to parathyroid hormone-related peptide (PTHrP). Hypertrophic
pulmonary osteoarthropathy is seen with non-small cell lung cancers, particularly
adenocarcinoma. Gynecomastia can be seen with human chorionic gonadotropin
(hCG) secretion from large cell carcinoma, and carcinoid syndrome occurs with
carcinoid tumors, typically in the GI tract or bronchus, but is less common than
SIADH in SCLC.
---
Question 4
A 32-year-old woman presents with episodic palpitations, diaphoresis, and severe
headaches. She is found to have hypertension that is poorly controlled on multiple
medications. A 24-hour urine collection shows elevated metanephrines. Which of
the following genetic syndromes is most strongly associated with this condition?
A) Neurofibromatosis type 1
B) Multiple endocrine neoplasia type 2A
C) Von Hippel-Lindau disease
D) Tuberous sclerosis
E) Li-Fraumeni syndrome
Answer: B) Multiple endocrine neoplasia type 2A
Rationale: The clinical presentation of episodic hypertension, palpitations,
diaphoresis, and headaches, along with elevated urinary metanephrines, is
diagnostic for pheochromocytoma, a catecholamine-secreting tumor of the adrenal
medulla. Pheochromocytoma is a hallmark feature of MEN 2A, which also
includes medullary thyroid carcinoma and primary hyperparathyroidism, all due to
a germline mutation in the RET proto-oncogene. Neurofibromatosis type 1 and
Von Hippel-Lindau disease are also associated with pheochromocytoma but are
less strongly linked than MEN 2A in the classic triad. Tuberous sclerosis causes
hamartomas and angiofibromas, not pheochromocytoma, and Li-Fraumeni is
associated with sarcomas and early-onset breast cancer.
---
, Question 5
A 55-year-old male with a history of hepatitis C presents with ascites, jaundice,
and confusion. On physical exam, he has spider angiomas and palmar erythema.
Laboratory studies show elevated ammonia. Which of the following is the primary
mechanism of hepatic encephalopathy in this patient?
A) Accumulation of gamma-aminobutyric acid (GABA)
B) Increased cerebral uptake of aromatic amino acids
C) Direct hepatocyte injury from ammonia
D) Decreased clearance of ammonia by the liver leading to astrocyte swelling
E) Portosystemic shunting of insulin
Answer: D) Decreased clearance of ammonia by the liver leading to astrocyte
swelling
Rationale: In chronic liver disease, such as that from hepatitis C, impaired hepatic
function and portosystemic shunting lead to increased systemic ammonia.
Ammonia crosses the blood-brain barrier and is taken up by astrocytes, where it is
converted to glutamine. The accumulation of glutamine increases intracellular
osmotic pressure, causing astrocyte swelling and cerebral edema, which
contributes to the altered mental status seen in hepatic encephalopathy. GABA
accumulation is a secondary effect, not the primary mechanism. Aromatic amino
acids increase but this is related to altered neurotransmitter balance, not the direct
cause. Hepatocyte injury from ammonia is not the mechanism, and insulin shunting
is not directly implicated in encephalopathy.
---
Question 6
A 7-year-old child presents with recurrent respiratory infections and failure to
thrive. Sweat chloride testing is positive. Genetic testing reveals a mutation in the
CFTR gene. Which of the following cellular mechanisms is primarily disrupted in
this condition?
A) Defective sodium reabsorption in the renal tubules
B) Impaired chloride secretion and increased sodium absorption in epithelial cells
C) Decreased mucus production in the lungs
D) Enhanced bicarbonate secretion in the pancreas
E) Defective ciliary movement in the respiratory tract
Answer: B) Impaired chloride secretion and increased sodium absorption in
epithelial cells
