Diabetes Mellitus USMLE Step 1 Practice Question
A 67 year old man with a 50 pack year smoking history is brought for confusion. He has no edema. Serum sodium is 118 mEq/L, serum osmolality is low, and urine osmolality is inappropriately high. Chest imaging shows a central lung mass. Which of the following is the most likely cause of his electrolyte abnormality?
Answer choices
- AEctopic ADH production by small cell carcinomaCorrect answer
- BRenal resistance to ADH from lithium use
- CLoss of aldosterone synthesis due to adrenal destruction
- DOsmotic diuresis from uncontrolled diabetes mellitus
- EPrimary polydipsia with suppressed ADH
- FExcessive free water intake from impaired thirst mechanism due to CNS metastases
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.