2026/2027
NBME CBSE (USMLE Step 1
Medical Exam) Comprehensive
Study Companion for Test Prep,
Review Questions, and Practice
Assessments 2026/2027
Question 1
A 70-year-old man dies in a motor vehicle collision and was previously undergoing
evaluation for occult blood in stool. A transverse colon lesion is shown on pathology.
Which is the most likely diagnosis?
A. Adenocarcinoma of colon
B. Tubular adenoma or villous polyp
C. Diverticulitis
D. Crohn disease
Correct Answer: B. Tubular adenoma or villous polyp
Rationale: Tubular adenomas and villous adenomas are premalignant colonic polyps
strongly associated with occult gastrointestinal bleeding and increased risk of
progression to colorectal cancer. Villous adenomas in particular have a higher
malignant potential. Adenocarcinoma would represent a later malignant stage, while
diverticulitis and Crohn disease typically present with inflammatory changes rather
than isolated polypoid lesions causing occult bleeding.
Question 2
A 38-year-old truck driver presents with 1-week history of watery eyes, nasal itching,
and rhinorrhea. Physical exam shows inflamed nasal mucosa without lower
respiratory involvement. Which pharmacologic agent is most appropriate?
A. Diphenhydramine
B. Loratadine
C. Albuterol
D. Oxymetazoline
Correct Answer: B. Loratadine
Rationale: Loratadine is a second-generation antihistamine that is effective in treating
allergic rhinitis while minimizing sedation due to poor CNS penetration.
,2026/2027
Diphenhydramine is sedating, albuterol is used for bronchospasm, and oxymetazoline
is a topical decongestant appropriate only for short-term use due to rebound
congestion.
Question 3
A 16-year-old girl presents with fever, fatigue, and bilateral interstitial infiltrates on
chest X-ray. Blood samples show spontaneous agglutination due to antibody-mediated
RBC clumping. Which antibody class is responsible?
A. IgA
B. IgE
C. IgG
D. IgM
Correct Answer: D. IgM
Rationale: IgM antibodies are efficient at agglutination due to their pentameric
structure and are classically associated with cold agglutinin disease seen in infections
like Mycoplasma pneumoniae. IgG is more involved in secondary immune responses
and opsonization, while IgA and IgE are associated with mucosal immunity and
allergic responses respectively.
Question 4
A 24-year-old man presents with painful genital vesicles 3 days after unprotected
intercourse. Which organism is the most likely cause?
A. Treponema pallidum
B. Herpes simplex virus type 2
C. Chlamydia trachomatis
D. Neisseria gonorrhoeae
Correct Answer: B. Herpes simplex virus type 2
Rationale: HSV-2 is the most common cause of painful genital vesicular lesions.
Syphilis typically presents with painless chancres, while chlamydia and gonorrhea
cause urethritis and discharge rather than vesicles.
Question 5
A 42-year-old woman has facial flushing and erythema over cheeks and nose with
telangiectasias worsened by spicy foods. What is the most likely diagnosis?
,2026/2027
A. Systemic lupus erythematosus
B. Rosacea
C. Seborrheic dermatitis
D. Contact dermatitis
Correct Answer: B. Rosacea
Rationale: Rosacea presents with central facial erythema, flushing, papules, and
telangiectasia triggered by heat, alcohol, and spicy foods. SLE would include
systemic symptoms and malar rash sparing nasolabial folds. Seborrheic dermatitis
affects sebaceous areas with scaling.
Question 6
A 53-year-old man returns from Africa with fever, headache, and ring-shaped
organisms in RBCs on smear. Diagnosis?
A. Babesiosis
B. Malaria
C. Trypanosomiasis
D. Leishmaniasis
Correct Answer: B. Malaria
Rationale: Malaria caused by Plasmodium species produces intraerythrocytic ring
forms on smear. Babesiosis also infects RBCs but classically shows Maltese cross
formations and occurs in tick-endemic regions.
Question 7
A 68-year-old woman with diabetes and hypertension has proteinuria and poorly
controlled BP. Which medication is most appropriate?
A. Furosemide
B. ACE inhibitor (Lisinopril)
C. Atenolol
D. Hydralazine
Correct Answer: B. ACE inhibitor (Lisinopril)
Rationale: ACE inhibitors reduce intraglomerular pressure and proteinuria while
slowing diabetic nephropathy progression. Beta blockers and diuretics control BP but
do not provide renal protection.
Question 8
, 2026/2027
A 66-year-old man develops severe diarrhea after chemotherapy with irinotecan.
Which antidiarrheal is appropriate without CNS effects?
A. Diphenoxylate
B. Loperamide
C. Atropine
D. Morphine
Correct Answer: B. Loperamide
Rationale: Loperamide acts on peripheral opioid receptors in the gut without crossing
the blood-brain barrier, reducing GI motility. Diphenoxylate and morphine can cause
CNS effects and dependence.
Question 9
A 35-year-old man with severe dehydration after cholera infection presents with
watery diarrhea. Which toxin mechanism is responsible?
A. Inhibition of adenylate cyclase
B. Activation of adenylate cyclase
C. Increased cGMP breakdown
D. Ribosomal inhibition
Correct Answer: B. Activation of adenylate cyclase
Rationale: Cholera toxin activates adenylate cyclase via Gs protein stimulation,
increasing cAMP and causing chloride and water secretion. This leads to profuse
watery diarrhea.
Question 10
A newborn presents with microcephaly, petechial rash, and hepatosplenomegaly.
Mother has IgG positive CMV, newborn IgM positive. Diagnosis?
A. Congenital toxoplasmosis
B. Congenital CMV infection
C. Rubella syndrome
D. HSV infection
Correct Answer: B. Congenital CMV infection
Rationale: Congenital CMV presents with “blueberry muffin” rash, microcephaly, and
hepatosplenomegaly. IgM positivity in the newborn confirms active infection.
NBME CBSE (USMLE Step 1
Medical Exam) Comprehensive
Study Companion for Test Prep,
Review Questions, and Practice
Assessments 2026/2027
Question 1
A 70-year-old man dies in a motor vehicle collision and was previously undergoing
evaluation for occult blood in stool. A transverse colon lesion is shown on pathology.
Which is the most likely diagnosis?
A. Adenocarcinoma of colon
B. Tubular adenoma or villous polyp
C. Diverticulitis
D. Crohn disease
Correct Answer: B. Tubular adenoma or villous polyp
Rationale: Tubular adenomas and villous adenomas are premalignant colonic polyps
strongly associated with occult gastrointestinal bleeding and increased risk of
progression to colorectal cancer. Villous adenomas in particular have a higher
malignant potential. Adenocarcinoma would represent a later malignant stage, while
diverticulitis and Crohn disease typically present with inflammatory changes rather
than isolated polypoid lesions causing occult bleeding.
Question 2
A 38-year-old truck driver presents with 1-week history of watery eyes, nasal itching,
and rhinorrhea. Physical exam shows inflamed nasal mucosa without lower
respiratory involvement. Which pharmacologic agent is most appropriate?
A. Diphenhydramine
B. Loratadine
C. Albuterol
D. Oxymetazoline
Correct Answer: B. Loratadine
Rationale: Loratadine is a second-generation antihistamine that is effective in treating
allergic rhinitis while minimizing sedation due to poor CNS penetration.
,2026/2027
Diphenhydramine is sedating, albuterol is used for bronchospasm, and oxymetazoline
is a topical decongestant appropriate only for short-term use due to rebound
congestion.
Question 3
A 16-year-old girl presents with fever, fatigue, and bilateral interstitial infiltrates on
chest X-ray. Blood samples show spontaneous agglutination due to antibody-mediated
RBC clumping. Which antibody class is responsible?
A. IgA
B. IgE
C. IgG
D. IgM
Correct Answer: D. IgM
Rationale: IgM antibodies are efficient at agglutination due to their pentameric
structure and are classically associated with cold agglutinin disease seen in infections
like Mycoplasma pneumoniae. IgG is more involved in secondary immune responses
and opsonization, while IgA and IgE are associated with mucosal immunity and
allergic responses respectively.
Question 4
A 24-year-old man presents with painful genital vesicles 3 days after unprotected
intercourse. Which organism is the most likely cause?
A. Treponema pallidum
B. Herpes simplex virus type 2
C. Chlamydia trachomatis
D. Neisseria gonorrhoeae
Correct Answer: B. Herpes simplex virus type 2
Rationale: HSV-2 is the most common cause of painful genital vesicular lesions.
Syphilis typically presents with painless chancres, while chlamydia and gonorrhea
cause urethritis and discharge rather than vesicles.
Question 5
A 42-year-old woman has facial flushing and erythema over cheeks and nose with
telangiectasias worsened by spicy foods. What is the most likely diagnosis?
,2026/2027
A. Systemic lupus erythematosus
B. Rosacea
C. Seborrheic dermatitis
D. Contact dermatitis
Correct Answer: B. Rosacea
Rationale: Rosacea presents with central facial erythema, flushing, papules, and
telangiectasia triggered by heat, alcohol, and spicy foods. SLE would include
systemic symptoms and malar rash sparing nasolabial folds. Seborrheic dermatitis
affects sebaceous areas with scaling.
Question 6
A 53-year-old man returns from Africa with fever, headache, and ring-shaped
organisms in RBCs on smear. Diagnosis?
A. Babesiosis
B. Malaria
C. Trypanosomiasis
D. Leishmaniasis
Correct Answer: B. Malaria
Rationale: Malaria caused by Plasmodium species produces intraerythrocytic ring
forms on smear. Babesiosis also infects RBCs but classically shows Maltese cross
formations and occurs in tick-endemic regions.
Question 7
A 68-year-old woman with diabetes and hypertension has proteinuria and poorly
controlled BP. Which medication is most appropriate?
A. Furosemide
B. ACE inhibitor (Lisinopril)
C. Atenolol
D. Hydralazine
Correct Answer: B. ACE inhibitor (Lisinopril)
Rationale: ACE inhibitors reduce intraglomerular pressure and proteinuria while
slowing diabetic nephropathy progression. Beta blockers and diuretics control BP but
do not provide renal protection.
Question 8
, 2026/2027
A 66-year-old man develops severe diarrhea after chemotherapy with irinotecan.
Which antidiarrheal is appropriate without CNS effects?
A. Diphenoxylate
B. Loperamide
C. Atropine
D. Morphine
Correct Answer: B. Loperamide
Rationale: Loperamide acts on peripheral opioid receptors in the gut without crossing
the blood-brain barrier, reducing GI motility. Diphenoxylate and morphine can cause
CNS effects and dependence.
Question 9
A 35-year-old man with severe dehydration after cholera infection presents with
watery diarrhea. Which toxin mechanism is responsible?
A. Inhibition of adenylate cyclase
B. Activation of adenylate cyclase
C. Increased cGMP breakdown
D. Ribosomal inhibition
Correct Answer: B. Activation of adenylate cyclase
Rationale: Cholera toxin activates adenylate cyclase via Gs protein stimulation,
increasing cAMP and causing chloride and water secretion. This leads to profuse
watery diarrhea.
Question 10
A newborn presents with microcephaly, petechial rash, and hepatosplenomegaly.
Mother has IgG positive CMV, newborn IgM positive. Diagnosis?
A. Congenital toxoplasmosis
B. Congenital CMV infection
C. Rubella syndrome
D. HSV infection
Correct Answer: B. Congenital CMV infection
Rationale: Congenital CMV presents with “blueberry muffin” rash, microcephaly, and
hepatosplenomegaly. IgM positivity in the newborn confirms active infection.
