A patient presents with polydipsia and polyuria. Laboratory tests show high plasma osmolality and low urine osmolality, which does not improve after administration of desmopressin (synthetic ADH). Which of the following is the most likely diagnosis?

The correct answer to the question "A patient presents with polydipsia and polyuria. Laboratory tests show high plasma osmolality and low urine osmolality, which does not improve after administration of desmopressin (synthetic ADH). Which of the following is the most likely diagnosis?" is Option B: Nephrogenic diabetes insipidus.

The other options — A) Central diabetes insipidus, C) Syndrome of inappropriate ADH (SIADH), D) Primary polydipsia — are incorrect for this USMLE Exam Prep question. As explained above: In nephrogenic diabetes insipidus, the kidneys are resistant to ADH. Therefore, desmopressin (ADH analog) administration will not improve the urine osmolality. Central DI would show improvement, whil…