NBME CBSE-Style Comprehensive
Practice Examination- COMPLETE (100)
CURRENT TESTING QUESTIONS AND
CORRECT ANSWERS WITH DETAILED
EXPLANATIONS.
These are original NBME/CBSE-style practice questions, not recalled or
reproduced questions from an actual examination. Each question has one
best answer.
Question 1
A 22-year-old woman presents with fatigue, weight loss, heat intolerance,
and palpitations. She has a diffusely enlarged thyroid and bilateral lid
retraction. Laboratory studies show increased serum free thyroxine and
decreased thyroid-stimulating hormone. Which of the following mechanisms
best explains her condition?
A. Antibodies that destroy thyroid follicular cells
B. Antibodies that stimulate the TSH receptor
C. Increased secretion of thyrotropin-releasing hormone
D. Activating mutation of the calcium-sensing receptor
E. Decreased conversion of T4 to T3
,ANSWER: B. Antibodies that stimulate the TSH receptor
Rationale: This patient has Graves disease, an autoimmune cause of
hyperthyroidism. IgG autoantibodies bind and activate the TSH receptor,
causing increased synthesis and release of thyroid hormones and diffuse
thyroid enlargement. The antibodies can also stimulate orbital fibroblasts,
producing ophthalmopathy.
A: Hashimoto thyroiditis involves autoimmune destruction of thyroid tissue
and typically causes hypothyroidism.
C: Increased TRH would increase TSH, which is inconsistent with this
patient's suppressed TSH.
D: Calcium-sensing receptor abnormalities cause disorders of calcium
metabolism.
E: Reduced T4-to-T3 conversion would generally reduce active thyroid
hormone.
Question 2
A 65-year-old man with a 50-pack-year smoking history develops progressive
cough, weight loss, and weakness. Laboratory studies show serum sodium of
119 mEq/L. Serum osmolality is decreased, urine osmolality is increased, and
urine sodium is elevated. A chest radiograph shows a hilar mass. Which of
the following is most likely responsible for his electrolyte abnormality?
A. Increased aldosterone secretion
B. Increased atrial natriuretic peptide secretion
C. Ectopic antidiuretic hormone secretion
D. Renal resistance to antidiuretic hormone
E. Excess cortisol secretion
,ANSWER: C. Ectopic antidiuretic hormone secretion
Rationale: A smoker with a hilar mass, profound euvolemic hyponatremia,
low serum osmolality, and inappropriately concentrated urine most likely has
small cell lung carcinoma producing ectopic ADH. ADH increases water
reabsorption through V2 receptors in the collecting ducts, producing
dilutional hyponatremia.
A: Aldosterone increases sodium retention and potassium excretion.
B: ANP promotes natriuresis and would not explain concentrated urine in this
setting.
D: ADH resistance causes dilute urine and hypernatremia.
E: Cortisol excess can cause hypertension, hyperglycemia, and hypokalemia
but does not produce this classic laboratory pattern.
Question 3
A 7-year-old boy is brought to the physician because of recurrent infections.
He has chronic diarrhea, failure to thrive, and absent tonsils. Laboratory
testing shows markedly decreased levels of immunoglobulins and circulating
mature B cells. Which of the following genetic defects is most likely?
A. Defective CD40 ligand
B. Defective Bruton's tyrosine kinase
C. Defective NADPH oxidase
D. Defective adenosine deaminase
E. Defective C5 complement component
ANSWER: B. Defective Bruton's tyrosine kinase
, Rationale: X-linked agammaglobulinemia results from defective Bruton's
tyrosine kinase, which is required for B-cell maturation. Patients develop
markedly decreased mature B cells and immunoglobulins and recurrent
infections, particularly with encapsulated bacteria, after maternal IgG
wanes.
A: CD40L deficiency causes hyper-IgM syndrome with impaired class
switching.
C: NADPH oxidase deficiency causes chronic granulomatous disease.
D: ADA deficiency causes severe combined immunodeficiency.
E: C5 deficiency predisposes particularly to Neisseria infections.
Question 4
A 34-year-old woman presents with recurrent episodes of severe abdominal
pain. She has no fever, vomiting, or diarrhea. Her brother has similar
episodes. Laboratory testing demonstrates elevated urinary porphobilinogen
during an attack. Which of the following enzymes is deficient?
A. ALA dehydratase
B. Ferrochelatase
C. Porphobilinogen deaminase
D. Uroporphyrinogen decarboxylase
E. Coproporphyrinogen oxidase
ANSWER: C. Porphobilinogen deaminase
Rationale: Acute intermittent porphyria is caused by deficiency of
porphobilinogen deaminase. It presents with episodic abdominal pain,
Practice Examination- COMPLETE (100)
CURRENT TESTING QUESTIONS AND
CORRECT ANSWERS WITH DETAILED
EXPLANATIONS.
These are original NBME/CBSE-style practice questions, not recalled or
reproduced questions from an actual examination. Each question has one
best answer.
Question 1
A 22-year-old woman presents with fatigue, weight loss, heat intolerance,
and palpitations. She has a diffusely enlarged thyroid and bilateral lid
retraction. Laboratory studies show increased serum free thyroxine and
decreased thyroid-stimulating hormone. Which of the following mechanisms
best explains her condition?
A. Antibodies that destroy thyroid follicular cells
B. Antibodies that stimulate the TSH receptor
C. Increased secretion of thyrotropin-releasing hormone
D. Activating mutation of the calcium-sensing receptor
E. Decreased conversion of T4 to T3
,ANSWER: B. Antibodies that stimulate the TSH receptor
Rationale: This patient has Graves disease, an autoimmune cause of
hyperthyroidism. IgG autoantibodies bind and activate the TSH receptor,
causing increased synthesis and release of thyroid hormones and diffuse
thyroid enlargement. The antibodies can also stimulate orbital fibroblasts,
producing ophthalmopathy.
A: Hashimoto thyroiditis involves autoimmune destruction of thyroid tissue
and typically causes hypothyroidism.
C: Increased TRH would increase TSH, which is inconsistent with this
patient's suppressed TSH.
D: Calcium-sensing receptor abnormalities cause disorders of calcium
metabolism.
E: Reduced T4-to-T3 conversion would generally reduce active thyroid
hormone.
Question 2
A 65-year-old man with a 50-pack-year smoking history develops progressive
cough, weight loss, and weakness. Laboratory studies show serum sodium of
119 mEq/L. Serum osmolality is decreased, urine osmolality is increased, and
urine sodium is elevated. A chest radiograph shows a hilar mass. Which of
the following is most likely responsible for his electrolyte abnormality?
A. Increased aldosterone secretion
B. Increased atrial natriuretic peptide secretion
C. Ectopic antidiuretic hormone secretion
D. Renal resistance to antidiuretic hormone
E. Excess cortisol secretion
,ANSWER: C. Ectopic antidiuretic hormone secretion
Rationale: A smoker with a hilar mass, profound euvolemic hyponatremia,
low serum osmolality, and inappropriately concentrated urine most likely has
small cell lung carcinoma producing ectopic ADH. ADH increases water
reabsorption through V2 receptors in the collecting ducts, producing
dilutional hyponatremia.
A: Aldosterone increases sodium retention and potassium excretion.
B: ANP promotes natriuresis and would not explain concentrated urine in this
setting.
D: ADH resistance causes dilute urine and hypernatremia.
E: Cortisol excess can cause hypertension, hyperglycemia, and hypokalemia
but does not produce this classic laboratory pattern.
Question 3
A 7-year-old boy is brought to the physician because of recurrent infections.
He has chronic diarrhea, failure to thrive, and absent tonsils. Laboratory
testing shows markedly decreased levels of immunoglobulins and circulating
mature B cells. Which of the following genetic defects is most likely?
A. Defective CD40 ligand
B. Defective Bruton's tyrosine kinase
C. Defective NADPH oxidase
D. Defective adenosine deaminase
E. Defective C5 complement component
ANSWER: B. Defective Bruton's tyrosine kinase
, Rationale: X-linked agammaglobulinemia results from defective Bruton's
tyrosine kinase, which is required for B-cell maturation. Patients develop
markedly decreased mature B cells and immunoglobulins and recurrent
infections, particularly with encapsulated bacteria, after maternal IgG
wanes.
A: CD40L deficiency causes hyper-IgM syndrome with impaired class
switching.
C: NADPH oxidase deficiency causes chronic granulomatous disease.
D: ADA deficiency causes severe combined immunodeficiency.
E: C5 deficiency predisposes particularly to Neisseria infections.
Question 4
A 34-year-old woman presents with recurrent episodes of severe abdominal
pain. She has no fever, vomiting, or diarrhea. Her brother has similar
episodes. Laboratory testing demonstrates elevated urinary porphobilinogen
during an attack. Which of the following enzymes is deficient?
A. ALA dehydratase
B. Ferrochelatase
C. Porphobilinogen deaminase
D. Uroporphyrinogen decarboxylase
E. Coproporphyrinogen oxidase
ANSWER: C. Porphobilinogen deaminase
Rationale: Acute intermittent porphyria is caused by deficiency of
porphobilinogen deaminase. It presents with episodic abdominal pain,
