COMSAE Phase 1 Form 116 Practice Exam
with Actual Questions & Verified Answers,
Plus Explained Rationales
Question 1: A 45-year-old man presents with progressive muscle weakness and
elevated serum creatine kinase levels. Muscle biopsy reveals endomysial
inflammation with CD8+ T-cell infiltration. Which of the following is the most
likely diagnosis?
A. Dermatomyositis
B. Inclusion body myositis
C. Polymyositis
D. Myasthenia gravis
CORRECT ANSWER: C. Polymyositis
Rationale: Polymyositis is characterized by CD8+ T-cell mediated endomysial
inflammation on muscle biopsy, leading to symmetric proximal muscle weakness
and elevated CK levels. Dermatomyositis involves perimysial inflammation and skin
findings, while inclusion body myositis shows rimmed vacuoles and affects distal
muscles more often in older patients. Myasthenia gravis involves neuromuscular
junction autoantibodies without primary muscle inflammation.
Question 2: Which of the following enzymes is primarily responsible for the
rate-limiting step in cholesterol biosynthesis?
A. HMG-CoA reductase
B. Acetyl-CoA carboxylase
C. Phosphofructokinase-1
D. Pyruvate dehydrogenase
CORRECT ANSWER: A. HMG-CoA reductase
Rationale: HMG-CoA reductase catalyzes the conversion of HMG-CoA to
mevalonate, the committed and rate-limiting step in the mevalonate pathway for
cholesterol synthesis. This enzyme is the target of statin drugs. The other enzymes
are involved in fatty acid synthesis or glycolysis.
Question 3: A patient with a history of recurrent sinopulmonary infections is
found to have low levels of all immunoglobulin isotypes. Flow cytometry
shows absent B cells. Which immunodeficiency is most likely?
A. Common variable immunodeficiency
B. X-linked agammaglobulinemia
C. Selective IgA deficiency
D. Hyper-IgM syndrome
CORRECT ANSWER: B. X-linked agammaglobulinemia
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,Rationale: X-linked agammaglobulinemia (Bruton's) results from BTK mutation
leading to absent mature B cells and pan-hypogammaglobulinemia, causing
recurrent bacterial infections after 6 months of age. CVID has B cells present but
impaired function; selective IgA lacks only IgA; Hyper-IgM has normal/high IgM but
low other isotypes.
Question 4: During embryonic development, failure of the ductus arteriosus to
close after birth results in which congenital heart defect?
A. Tetralogy of Fallot
B. Patent ductus arteriosus
C. Atrial septal defect
D. Ventricular septal defect
CORRECT ANSWER: B. Patent ductus arteriosus
Rationale: Patent ductus arteriosus (PDA) occurs when the fetal shunt between
pulmonary artery and aorta fails to close postnatally, leading to left-to-right shunt.
It is common in premature infants and can cause machinery murmur. The other
defects involve different embryologic septation or outflow tract issues.
Question 5: A 55-year-old woman with rheumatoid arthritis develops
proteinuria and hematuria. Renal biopsy shows focal segmental
glomerulosclerosis. Which drug is most likely responsible?
A. Methotrexate
B. Hydroxychloroquine
C. Gold therapy (historical)
D. Penicillamine
CORRECT ANSWER: D. Penicillamine
Rationale: Penicillamine, used historically in RA, is associated with membranous
nephropathy or other glomerular diseases leading to proteinuria. Methotrexate is
hepatotoxic; hydroxychloroquine affects retina primarily.
Question 6: Which of the following hormones is secreted by the zona
glomerulosa of the adrenal cortex?
A. Cortisol
B. Aldosterone
C. Androstenedione
D. Epinephrine
CORRECT ANSWER: B. Aldosterone
Rationale: The zona glomerulosa produces mineralocorticoids like aldosterone
under renin-angiotensin regulation. Zona fasciculata produces glucocorticoids
(cortisol), reticularis androgens, and medulla catecholamines.
Question 7: A patient with chronic granulomatous disease is susceptible to
infections by which organism due to defective NADPH oxidase?
A. Streptococcus pneumoniae
B. Staphylococcus aureus (catalase-positive)
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,C. Neisseria meningitidis
D. Haemophilus influenzae
Page 3 of 31
, CORRECT ANSWER: B. Staphylococcus aureus (catalase-positive)
Rationale: CGD impairs oxidative burst, making patients vulnerable to catalase-
positive organisms like S. aureus that degrade their own H2O2. Catalase-negative
organisms provide H2O2 that neutrophils can use.
Question 8: In glycolysis, the enzyme that catalyzes the irreversible conversion
of phosphoenolpyruvate to pyruvate is:
A. Hexokinase
B. Pyruvate kinase
C. Phosphoglycerate kinase
D. Aldolase
CORRECT ANSWER: B. Pyruvate kinase
Rationale: Pyruvate kinase performs the final irreversible step of glycolysis,
generating ATP. Deficiencies cause hemolytic anemia. Hexokinase is the first step.
Question 9: A 30-year-old man sustains a fracture of the surgical neck of the
humerus. Which nerve is most at risk of injury?
A. Radial nerve
B. Axillary nerve
C. Median nerve
D. Ulnar nerve
CORRECT ANSWER: B. Axillary nerve
Rationale: The axillary nerve wraps around the surgical neck of the humerus and is
commonly injured in fractures there, leading to deltoid weakness and lateral
shoulder sensory loss. Radial nerve is at risk in mid-shaft fractures.
Question 10: Which of the following is a classic side effect of thiazide
diuretics?
A. Hyperkalemia
B. Hyponatremia
C. Metabolic acidosis
D. Hypercalcemia
CORRECT ANSWER: D. Hypercalcemia
Rationale: Thiazides reduce urinary calcium excretion, leading to hypercalcemia,
while causing hypokalemia, hyponatremia, and metabolic alkalosis. Loop diuretics
cause hypocalcemia.
1. A 24-year-old male presents with a "waiter's tip" posture of his right
upper extremity after a motorcycle accident. Which nerve roots are most
likely injured?
A) C5-C6
B) C7-C8
C) C8-T1
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with Actual Questions & Verified Answers,
Plus Explained Rationales
Question 1: A 45-year-old man presents with progressive muscle weakness and
elevated serum creatine kinase levels. Muscle biopsy reveals endomysial
inflammation with CD8+ T-cell infiltration. Which of the following is the most
likely diagnosis?
A. Dermatomyositis
B. Inclusion body myositis
C. Polymyositis
D. Myasthenia gravis
CORRECT ANSWER: C. Polymyositis
Rationale: Polymyositis is characterized by CD8+ T-cell mediated endomysial
inflammation on muscle biopsy, leading to symmetric proximal muscle weakness
and elevated CK levels. Dermatomyositis involves perimysial inflammation and skin
findings, while inclusion body myositis shows rimmed vacuoles and affects distal
muscles more often in older patients. Myasthenia gravis involves neuromuscular
junction autoantibodies without primary muscle inflammation.
Question 2: Which of the following enzymes is primarily responsible for the
rate-limiting step in cholesterol biosynthesis?
A. HMG-CoA reductase
B. Acetyl-CoA carboxylase
C. Phosphofructokinase-1
D. Pyruvate dehydrogenase
CORRECT ANSWER: A. HMG-CoA reductase
Rationale: HMG-CoA reductase catalyzes the conversion of HMG-CoA to
mevalonate, the committed and rate-limiting step in the mevalonate pathway for
cholesterol synthesis. This enzyme is the target of statin drugs. The other enzymes
are involved in fatty acid synthesis or glycolysis.
Question 3: A patient with a history of recurrent sinopulmonary infections is
found to have low levels of all immunoglobulin isotypes. Flow cytometry
shows absent B cells. Which immunodeficiency is most likely?
A. Common variable immunodeficiency
B. X-linked agammaglobulinemia
C. Selective IgA deficiency
D. Hyper-IgM syndrome
CORRECT ANSWER: B. X-linked agammaglobulinemia
Page 1 of 31
,Rationale: X-linked agammaglobulinemia (Bruton's) results from BTK mutation
leading to absent mature B cells and pan-hypogammaglobulinemia, causing
recurrent bacterial infections after 6 months of age. CVID has B cells present but
impaired function; selective IgA lacks only IgA; Hyper-IgM has normal/high IgM but
low other isotypes.
Question 4: During embryonic development, failure of the ductus arteriosus to
close after birth results in which congenital heart defect?
A. Tetralogy of Fallot
B. Patent ductus arteriosus
C. Atrial septal defect
D. Ventricular septal defect
CORRECT ANSWER: B. Patent ductus arteriosus
Rationale: Patent ductus arteriosus (PDA) occurs when the fetal shunt between
pulmonary artery and aorta fails to close postnatally, leading to left-to-right shunt.
It is common in premature infants and can cause machinery murmur. The other
defects involve different embryologic septation or outflow tract issues.
Question 5: A 55-year-old woman with rheumatoid arthritis develops
proteinuria and hematuria. Renal biopsy shows focal segmental
glomerulosclerosis. Which drug is most likely responsible?
A. Methotrexate
B. Hydroxychloroquine
C. Gold therapy (historical)
D. Penicillamine
CORRECT ANSWER: D. Penicillamine
Rationale: Penicillamine, used historically in RA, is associated with membranous
nephropathy or other glomerular diseases leading to proteinuria. Methotrexate is
hepatotoxic; hydroxychloroquine affects retina primarily.
Question 6: Which of the following hormones is secreted by the zona
glomerulosa of the adrenal cortex?
A. Cortisol
B. Aldosterone
C. Androstenedione
D. Epinephrine
CORRECT ANSWER: B. Aldosterone
Rationale: The zona glomerulosa produces mineralocorticoids like aldosterone
under renin-angiotensin regulation. Zona fasciculata produces glucocorticoids
(cortisol), reticularis androgens, and medulla catecholamines.
Question 7: A patient with chronic granulomatous disease is susceptible to
infections by which organism due to defective NADPH oxidase?
A. Streptococcus pneumoniae
B. Staphylococcus aureus (catalase-positive)
Page 2 of 31
,C. Neisseria meningitidis
D. Haemophilus influenzae
Page 3 of 31
, CORRECT ANSWER: B. Staphylococcus aureus (catalase-positive)
Rationale: CGD impairs oxidative burst, making patients vulnerable to catalase-
positive organisms like S. aureus that degrade their own H2O2. Catalase-negative
organisms provide H2O2 that neutrophils can use.
Question 8: In glycolysis, the enzyme that catalyzes the irreversible conversion
of phosphoenolpyruvate to pyruvate is:
A. Hexokinase
B. Pyruvate kinase
C. Phosphoglycerate kinase
D. Aldolase
CORRECT ANSWER: B. Pyruvate kinase
Rationale: Pyruvate kinase performs the final irreversible step of glycolysis,
generating ATP. Deficiencies cause hemolytic anemia. Hexokinase is the first step.
Question 9: A 30-year-old man sustains a fracture of the surgical neck of the
humerus. Which nerve is most at risk of injury?
A. Radial nerve
B. Axillary nerve
C. Median nerve
D. Ulnar nerve
CORRECT ANSWER: B. Axillary nerve
Rationale: The axillary nerve wraps around the surgical neck of the humerus and is
commonly injured in fractures there, leading to deltoid weakness and lateral
shoulder sensory loss. Radial nerve is at risk in mid-shaft fractures.
Question 10: Which of the following is a classic side effect of thiazide
diuretics?
A. Hyperkalemia
B. Hyponatremia
C. Metabolic acidosis
D. Hypercalcemia
CORRECT ANSWER: D. Hypercalcemia
Rationale: Thiazides reduce urinary calcium excretion, leading to hypercalcemia,
while causing hypokalemia, hyponatremia, and metabolic alkalosis. Loop diuretics
cause hypocalcemia.
1. A 24-year-old male presents with a "waiter's tip" posture of his right
upper extremity after a motorcycle accident. Which nerve roots are most
likely injured?
A) C5-C6
B) C7-C8
C) C8-T1
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