UWorld UWorld USMLE Step Preparation 5

Question 1

During surgery under sevoflurane and succinylcholine, a patient develops masseter rigidity, hyperthermia, and rising end-tidal CO2. What is the drug of choice?

Accepted Answer

Dantrolene

Answer

Dantrolene blocks ryanodine receptor calcium release in skeletal muscle, reversing malignant hyperthermia.

Question 2

A 9-month-old has episodic inconsolable crying with drawing up of the legs, currant jelly stools, and a sausage-shaped abdominal mass. What is the most likely diagnosis?

Accepted Answer

Intussusception

Answer

Intussusception classically presents with colicky pain, currant jelly stools, and a sausage-shaped mass, often at the ileocecal junction.

Question 3

A 68-year-old man has painless jaundice, weight loss, and a palpable non-tender gallbladder. What is the most likely diagnosis?

Accepted Answer

Adenocarcinoma of the pancreatic head

Answer

Courvoisier sign (palpable, non-tender gallbladder with painless jaundice) suggests malignant obstruction such as pancreatic head cancer.

Question 4

What is the mechanism of action of warfarin?

Accepted Answer

Inhibition of vitamin K epoxide reductase

Answer

Warfarin inhibits VKORC1, preventing gamma-carboxylation of factors II, VII, IX, X, and proteins C and S.

Question 5

A patient on long-term therapy for bipolar disorder develops polyuria and dilute urine that does not concentrate after desmopressin. Which drug is most likely responsible?

Accepted Answer

Lithium

Answer

Lithium causes nephrogenic diabetes insipidus by impairing ADH response in the collecting duct.

UWorld Practice Test

UWorld Practice Test

UWorld UWorld USMLE Step Preparation 5