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?

✓ Correct Answer: Option B

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, while SIADH presents with low plasma osmolality.