UWorld USMLE Step Preparation Flashcards

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

Answer: Dantrolene

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

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?

Answer: Intussusception

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

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

Answer: Adenocarcinoma of the pancreatic head

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

What is the mechanism of action of warfarin?

Answer: Inhibition of vitamin K epoxide reductase

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

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?

Answer: Lithium

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

In a trial, 10% of controls and 6% of treated patients have a stroke. What is the number needed to treat to prevent one stroke?

Answer: 25

The absolute risk reduction is 4%, so NNT = 1/0.04 = 25.

A girl with short stature, a webbed neck, and primary amenorrhea has a 45,X karyotype. Which cardiac abnormality is most commonly associated?

Answer: Bicuspid aortic valve

Bicuspid aortic valve is the most common cardiac defect in Turner syndrome, often alongside coarctation of the aorta.