A 30-year-old man develops polyuria

USMLE Question Break Down Endocrinology

Welcome back to MedSmarter USMLE Style Question of the Week. Here’s the breakdown of another high-yield Endocrinology question for those preparing for your USMLE Step 1 or just to gain some knowledge. As always you want to begin by reading the last sentence of the vignette first to get an understanding of what the question is asking for.

Question Break Down of the Week:

A 30-year-old man develops polyuria. His nephrologist monitors him closely on a water deprivation test, and he continues to have increased urine output. A diagnosis of diabetes insipidus is made. The nephrologist orders an antidiuretic hormone level and determines that it is inappropriately elevated. Which of the following is the site of pathology in this patient?

(A) Adenohypophysis
(B) D1
(C) Pituitary function
(D) V1
(E) V2

The correct answer choice is E. The patient in the vignette has diabetes insipidus with an elevated antidiuretic hormone (ADH) level, which means that the ADH is not working on its target, the kidney. The problem is with the ADH receptors in the kidneys themselves, not in the brain or central nervous system. The only receptor in the kidney that is associated with diabetes insipidus with an elevated ADH level is the V2 receptor. Therefore, the site of pathology in this patient is the V2 receptor in the kidneys, which makes option E the correct answer.

Did you think the answer was different?

Did you think that the correct answer choice was other than E? You can view this video for a deeper discussion of why A, B, C, and D are not the correct answer choices.

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