COMSAE 115 EXAM LATEST QUESTIONS AND CORRECT ANSWERS
Q1. A 54-year-old male presents with severe, tearing chest pain radiating to his back. He has a
history of poorly controlled hypertension. PE reveals a diastolic murmur at the right upper
sternal border and a BP difference between his arms. CT angiogram shows an intimal flap in the
ascending aorta. The tissue primarily affected in this patient's condition is derived from which of
the following embryological sources?
A) Lateral plate mesoderm
B) Neural crest cells
C) Paraxial mesoderm
D) Endoderm
Answer: B. Rationale: The patient has an aortic dissection. The tunica media of the ascending
aorta and aortic arch is derived from neural crest cells. Lateral plate mesoderm forms the
appendicular skeleton and circulatory system (heart/blood vessels) but the specific smooth
muscle of the aorticopulmonary septum and ascending aorta is neural crest. Paraxial mesoderm
forms somites (muscle, bone). Endoderm forms gut lining.
Q2. A 28-year-old female presents with a painless, hard nodule on her thyroid gland. Fine
needle aspiration confirms medullary thyroid carcinoma. This tumor arises from parafollicular C
cells, which secrete calcitonin. These cells are embryologically derived from which of the
following?
A) First pharyngeal pouch
B) Second pharyngeal pouch
C) Third pharyngeal pouch
D) Fourth/Fifth pharyngeal pouch (Ultimobranchial body)
Answer: D. Rationale: Parafollicular C cells migrate from the ultimobranchial body (derived
from the 4th/5th pharyngeal pouch) into the thyroid gland. They secrete calcitonin. 1st pouch
forms middle ear; 2nd forms palatine tonsils; 3rd forms inferior parathyroids and thymus; 4th
forms superior parathyroids.
Q3. A 65-year-old male with a history of COPD presents with worsening dyspnea. ABG shows pH
7.32, PaCO2 68 mmHg, PaO2 55 mmHg, and HCO3 34 mEq/L. What is the primary acid-base
disorder, and what is the expected compensatory mechanism?
A) Metabolic acidosis; hyperventilation
B) Respiratory acidosis; renal retention of bicarbonate
C) Respiratory alkalosis; renal excretion of bicarbonate
D) Metabolic alkalosis; hypoventilation
Answer: B. Rationale: The low pH and high PaCO2 indicate respiratory acidosis (due to COPD
hypoventilation). The elevated HCO3 indicates metabolic compensation via renal retention of
bicarbonate. The compensation is chronic, hence the significant bicarbonate elevation.
,Q4. A 4-year-old boy presents with a barking cough and inspiratory stridor. He recently had a
mild URI. Lateral neck X-ray shows the "steeple sign." What is the most likely causative
organism?
A) Haemophilus influenzae type b
B) Parainfluenza virus
C) Respiratory syncytial virus
D) Corynebacterium diphtheriae
Answer: B. Rationale: The steeple sign and barking cough indicate croup
(laryngotracheobronchitis), most commonly caused by Parainfluenza virus. Hib causes
epiglottitis (thumbprint sign). RSV causes bronchiolitis. C. diphtheriae causes a
pseudomembrane.
Q5. A 30-year-old male is brought to the ED after a motorcycle accident. He has a severe head
injury. CT shows a lens-shaped (biconvex) hyperdensity crossing suture lines. Wait, lens-shaped
does *not* cross suture lines. Let's correct: CT shows a biconvex hyperdensity that does *not*
cross suture lines. Which vessel is most likely ruptured?
A) Middle meningeal artery
B) Bridging veins
C. Anterior communicating artery
D. Lenticulostriate arteries
Answer: A. Rationale: An epidural hematoma presents as a biconvex (lens-shaped)
hyperdensity that does not cross suture lines, typically caused by rupture of the middle
meningeal artery due to a temporal bone fracture. Subdural hematomas (bridging veins) are
crescent-shaped and cross suture lines.
Q6. A 45-year-old female presents with fatigue, weight gain, and cold intolerance. Labs show
elevated TSH and low free T4. She is started on levothyroxine. Which of the following
parameters will be used to monitor the adequacy of her treatment?
A) Free T3 levels
B) TSH levels
C) Thyroglobulin levels
D. Radioactive iodine uptake
Answer: B. Rationale: TSH is the most sensitive marker for monitoring primary hypothyroidism
treatment. The goal is to normalize TSH. Free T3 is not routinely monitored. Thyroglobulin is
used for thyroid cancer surveillance.
Q7. A 60-year-old male with a history of atrial fibrillation is started on warfarin. Three days later,
he develops necrotic skin lesions. This adverse effect is primarily due to the rapid depletion of
which of the following?
A) Factor II
B) Factor VII
C) Protein C
D) Factor X
,Answer: C. Rationale: Warfarin inhibits vitamin K-dependent factors (II, VII, IX, X) and proteins
C and S. Protein C has a very short half-life. Its rapid depletion before the depletion of
procoagulant factors leads to a transient hypercoagulable state, causing warfarin-induced skin
necrosis.
Q8. A 22-year-old male presents with a painless testicular mass. Ultrasound reveals a solid,
homogeneous intratesticular mass. Serum AFP is normal, but beta-hCG is slightly elevated.
What is the most likely diagnosis?
A) Seminoma
B) Yolk sac tumor
C) Embryonal carcinoma
D) Choriocarcinoma
Answer: A. Rationale: Seminomas are the most common testicular tumors. They typically
present as painless, homogeneous masses. AFP is always normal in pure seminomas. Beta-hCG
can be mildly elevated in about 15% of cases due to syncytiotrophoblast giant cells. Yolk sac
tumors have elevated AFP.
Q9. A 55-year-old male with a history of alcohol use disorder presents with confusion, ataxia,
and ophthalmoplegia. He is diagnosed with Wernicke encephalopathy. Which of the following
enzymes requires the deficient vitamin as a cofactor?
A) Transketolase
B) Tyrosine hydroxylase
C) Glutathione reductase
D) Methylmalonyl-CoA mutase
Answer: A. Rationale: Wernicke encephalopathy is caused by Vitamin B1 (thiamine) deficiency.
Thiamine pyrophosphate (TPP) is a cofactor for transketolase, pyruvate dehydrogenase, alpha-
ketoglutarate dehydrogenase, and branched-chain ketoacid dehydrogenase.
Q10. A 35-year-old female presents with a malar rash, joint pain, and proteinuria. Labs show
positive ANA and anti-dsDNA antibodies. She is diagnosed with Systemic Lupus Erythematosus
(SLE). Which of the following hypersensitivity reactions is primarily responsible for her renal
pathology?
A) Type I
B) Type II
C) Type III
D) Type IV
Answer: C. Rationale: SLE is characterized by the formation of immune complexes (antigen-
antibody complexes), which deposit in tissues like the glomeruli, causing a Type III
hypersensitivity reaction (immune complex-mediated). Type II is antibody-mediated (e.g.,
Goodpasture's). Type IV is T-cell mediated (e.g., contact dermatitis).
Q11. A 50-year-old male presents with right flank pain and hematuria. CT reveals a 4 cm renal
mass. He undergoes a nephrectomy. Pathology shows clear cells with abundant cytoplasmic
lipid and glycogen. What is the most likely diagnosis?
, A) Clear cell renal cell carcinoma
B) Papillary renal cell carcinoma
C) Chromophobe renal cell carcinoma
D) Oncocytoma
Answer: A. Rationale: Clear cell RCC is the most common type. The cells appear "clear"
because the lipid and glycogen are washed out during staining. It is associated with VHL gene
mutations on chromosome 3p. Papillary RCC has cuboidal cells forming papillae. Oncocytoma
has eosinophilic granular cells (mitochondria).
Q12. A 25-year-old female presents with a history of recurrent miscarriages and a deep vein
thrombosis. Labs show a prolonged PTT that does not correct with mixing study. She tests
positive for anticardiolipin antibodies. What is the most likely diagnosis?
A) Hemophilia A
B) von Willebrand disease
C) Antiphospholipid syndrome
D) Protein C deficiency
Answer: C. Rationale: Antiphospholipid syndrome (APS) causes arterial and venous thromboses
and recurrent miscarriages. It is associated with lupus anticoagulant (which prolongs PTT in vitro
but causes thrombosis in vivo and doesn't correct with mixing) and anticardiolipin antibodies.
Q13. A 60-year-old male with a history of peptic ulcer disease presents with tremors, confusion,
and tinnitus. He has been taking large amounts of an over-the-counter medication for his
arthritis. What is the most likely acid-base disturbance?
A) Primary respiratory alkalosis and primary metabolic acidosis
B) Primary metabolic alkalosis
C) Primary respiratory acidosis
D. Pure metabolic acidosis
Answer: A. Rationale: Salicylate (aspirin) toxicity causes a mixed acid-base disorder. It directly
stimulates the respiratory center causing a primary respiratory alkalosis early on. Later, it
uncouples oxidative phosphorylation and accumulates organic acids, causing a primary high
anion gap metabolic acidosis.
Q14. A 4-year-old boy presents with developmental delay, self-mutilating behavior (lip and
finger biting), and hyperuricemia. Urine shows orange "sand" crystals. What is the deficient
enzyme?
A) Adenosine deaminase
B) HGPRT
C. Xanthine oxidase
D. Branched-chain alpha-keto acid dehydrogenase
Answer: B. Rationale: Lesch-Nyhan syndrome is an X-linked recessive disorder caused by
HGPRT deficiency, leading to impaired purine salvage and excess uric acid production.
Symptoms include hyperuricemia, gout, choreoathetosis, and self-mutilation. ADA deficiency
causes SCID.
Q1. A 54-year-old male presents with severe, tearing chest pain radiating to his back. He has a
history of poorly controlled hypertension. PE reveals a diastolic murmur at the right upper
sternal border and a BP difference between his arms. CT angiogram shows an intimal flap in the
ascending aorta. The tissue primarily affected in this patient's condition is derived from which of
the following embryological sources?
A) Lateral plate mesoderm
B) Neural crest cells
C) Paraxial mesoderm
D) Endoderm
Answer: B. Rationale: The patient has an aortic dissection. The tunica media of the ascending
aorta and aortic arch is derived from neural crest cells. Lateral plate mesoderm forms the
appendicular skeleton and circulatory system (heart/blood vessels) but the specific smooth
muscle of the aorticopulmonary septum and ascending aorta is neural crest. Paraxial mesoderm
forms somites (muscle, bone). Endoderm forms gut lining.
Q2. A 28-year-old female presents with a painless, hard nodule on her thyroid gland. Fine
needle aspiration confirms medullary thyroid carcinoma. This tumor arises from parafollicular C
cells, which secrete calcitonin. These cells are embryologically derived from which of the
following?
A) First pharyngeal pouch
B) Second pharyngeal pouch
C) Third pharyngeal pouch
D) Fourth/Fifth pharyngeal pouch (Ultimobranchial body)
Answer: D. Rationale: Parafollicular C cells migrate from the ultimobranchial body (derived
from the 4th/5th pharyngeal pouch) into the thyroid gland. They secrete calcitonin. 1st pouch
forms middle ear; 2nd forms palatine tonsils; 3rd forms inferior parathyroids and thymus; 4th
forms superior parathyroids.
Q3. A 65-year-old male with a history of COPD presents with worsening dyspnea. ABG shows pH
7.32, PaCO2 68 mmHg, PaO2 55 mmHg, and HCO3 34 mEq/L. What is the primary acid-base
disorder, and what is the expected compensatory mechanism?
A) Metabolic acidosis; hyperventilation
B) Respiratory acidosis; renal retention of bicarbonate
C) Respiratory alkalosis; renal excretion of bicarbonate
D) Metabolic alkalosis; hypoventilation
Answer: B. Rationale: The low pH and high PaCO2 indicate respiratory acidosis (due to COPD
hypoventilation). The elevated HCO3 indicates metabolic compensation via renal retention of
bicarbonate. The compensation is chronic, hence the significant bicarbonate elevation.
,Q4. A 4-year-old boy presents with a barking cough and inspiratory stridor. He recently had a
mild URI. Lateral neck X-ray shows the "steeple sign." What is the most likely causative
organism?
A) Haemophilus influenzae type b
B) Parainfluenza virus
C) Respiratory syncytial virus
D) Corynebacterium diphtheriae
Answer: B. Rationale: The steeple sign and barking cough indicate croup
(laryngotracheobronchitis), most commonly caused by Parainfluenza virus. Hib causes
epiglottitis (thumbprint sign). RSV causes bronchiolitis. C. diphtheriae causes a
pseudomembrane.
Q5. A 30-year-old male is brought to the ED after a motorcycle accident. He has a severe head
injury. CT shows a lens-shaped (biconvex) hyperdensity crossing suture lines. Wait, lens-shaped
does *not* cross suture lines. Let's correct: CT shows a biconvex hyperdensity that does *not*
cross suture lines. Which vessel is most likely ruptured?
A) Middle meningeal artery
B) Bridging veins
C. Anterior communicating artery
D. Lenticulostriate arteries
Answer: A. Rationale: An epidural hematoma presents as a biconvex (lens-shaped)
hyperdensity that does not cross suture lines, typically caused by rupture of the middle
meningeal artery due to a temporal bone fracture. Subdural hematomas (bridging veins) are
crescent-shaped and cross suture lines.
Q6. A 45-year-old female presents with fatigue, weight gain, and cold intolerance. Labs show
elevated TSH and low free T4. She is started on levothyroxine. Which of the following
parameters will be used to monitor the adequacy of her treatment?
A) Free T3 levels
B) TSH levels
C) Thyroglobulin levels
D. Radioactive iodine uptake
Answer: B. Rationale: TSH is the most sensitive marker for monitoring primary hypothyroidism
treatment. The goal is to normalize TSH. Free T3 is not routinely monitored. Thyroglobulin is
used for thyroid cancer surveillance.
Q7. A 60-year-old male with a history of atrial fibrillation is started on warfarin. Three days later,
he develops necrotic skin lesions. This adverse effect is primarily due to the rapid depletion of
which of the following?
A) Factor II
B) Factor VII
C) Protein C
D) Factor X
,Answer: C. Rationale: Warfarin inhibits vitamin K-dependent factors (II, VII, IX, X) and proteins
C and S. Protein C has a very short half-life. Its rapid depletion before the depletion of
procoagulant factors leads to a transient hypercoagulable state, causing warfarin-induced skin
necrosis.
Q8. A 22-year-old male presents with a painless testicular mass. Ultrasound reveals a solid,
homogeneous intratesticular mass. Serum AFP is normal, but beta-hCG is slightly elevated.
What is the most likely diagnosis?
A) Seminoma
B) Yolk sac tumor
C) Embryonal carcinoma
D) Choriocarcinoma
Answer: A. Rationale: Seminomas are the most common testicular tumors. They typically
present as painless, homogeneous masses. AFP is always normal in pure seminomas. Beta-hCG
can be mildly elevated in about 15% of cases due to syncytiotrophoblast giant cells. Yolk sac
tumors have elevated AFP.
Q9. A 55-year-old male with a history of alcohol use disorder presents with confusion, ataxia,
and ophthalmoplegia. He is diagnosed with Wernicke encephalopathy. Which of the following
enzymes requires the deficient vitamin as a cofactor?
A) Transketolase
B) Tyrosine hydroxylase
C) Glutathione reductase
D) Methylmalonyl-CoA mutase
Answer: A. Rationale: Wernicke encephalopathy is caused by Vitamin B1 (thiamine) deficiency.
Thiamine pyrophosphate (TPP) is a cofactor for transketolase, pyruvate dehydrogenase, alpha-
ketoglutarate dehydrogenase, and branched-chain ketoacid dehydrogenase.
Q10. A 35-year-old female presents with a malar rash, joint pain, and proteinuria. Labs show
positive ANA and anti-dsDNA antibodies. She is diagnosed with Systemic Lupus Erythematosus
(SLE). Which of the following hypersensitivity reactions is primarily responsible for her renal
pathology?
A) Type I
B) Type II
C) Type III
D) Type IV
Answer: C. Rationale: SLE is characterized by the formation of immune complexes (antigen-
antibody complexes), which deposit in tissues like the glomeruli, causing a Type III
hypersensitivity reaction (immune complex-mediated). Type II is antibody-mediated (e.g.,
Goodpasture's). Type IV is T-cell mediated (e.g., contact dermatitis).
Q11. A 50-year-old male presents with right flank pain and hematuria. CT reveals a 4 cm renal
mass. He undergoes a nephrectomy. Pathology shows clear cells with abundant cytoplasmic
lipid and glycogen. What is the most likely diagnosis?
, A) Clear cell renal cell carcinoma
B) Papillary renal cell carcinoma
C) Chromophobe renal cell carcinoma
D) Oncocytoma
Answer: A. Rationale: Clear cell RCC is the most common type. The cells appear "clear"
because the lipid and glycogen are washed out during staining. It is associated with VHL gene
mutations on chromosome 3p. Papillary RCC has cuboidal cells forming papillae. Oncocytoma
has eosinophilic granular cells (mitochondria).
Q12. A 25-year-old female presents with a history of recurrent miscarriages and a deep vein
thrombosis. Labs show a prolonged PTT that does not correct with mixing study. She tests
positive for anticardiolipin antibodies. What is the most likely diagnosis?
A) Hemophilia A
B) von Willebrand disease
C) Antiphospholipid syndrome
D) Protein C deficiency
Answer: C. Rationale: Antiphospholipid syndrome (APS) causes arterial and venous thromboses
and recurrent miscarriages. It is associated with lupus anticoagulant (which prolongs PTT in vitro
but causes thrombosis in vivo and doesn't correct with mixing) and anticardiolipin antibodies.
Q13. A 60-year-old male with a history of peptic ulcer disease presents with tremors, confusion,
and tinnitus. He has been taking large amounts of an over-the-counter medication for his
arthritis. What is the most likely acid-base disturbance?
A) Primary respiratory alkalosis and primary metabolic acidosis
B) Primary metabolic alkalosis
C) Primary respiratory acidosis
D. Pure metabolic acidosis
Answer: A. Rationale: Salicylate (aspirin) toxicity causes a mixed acid-base disorder. It directly
stimulates the respiratory center causing a primary respiratory alkalosis early on. Later, it
uncouples oxidative phosphorylation and accumulates organic acids, causing a primary high
anion gap metabolic acidosis.
Q14. A 4-year-old boy presents with developmental delay, self-mutilating behavior (lip and
finger biting), and hyperuricemia. Urine shows orange "sand" crystals. What is the deficient
enzyme?
A) Adenosine deaminase
B) HGPRT
C. Xanthine oxidase
D. Branched-chain alpha-keto acid dehydrogenase
Answer: B. Rationale: Lesch-Nyhan syndrome is an X-linked recessive disorder caused by
HGPRT deficiency, leading to impaired purine salvage and excess uric acid production.
Symptoms include hyperuricemia, gout, choreoathetosis, and self-mutilation. ADA deficiency
causes SCID.
