Central Diabetes Insipidus as a Rare Cause of Polyuria

Central diabetes insipidus (CDI) is a rare condition characterized by arginine vasopressin deficiency, leading to persistent polyuria and polydipsia. Although it can present at any age, idiopathic CDI in young adults is uncommon and diagnostically challenging. Inflammatory conditions such as infundibuloneurohypophysitis must be considered, particularly when magnetic resonance imaging (MRI) reveals a thickened pituitary stalk and absence of the posterior pituitary bright spot. Early recognition and differentiation from diabetes mellitus, nephrogenic diabetes insipidus, and primary polydipsia are crucial for effective management. We report the case of a 20-year-old male who presented with excessive urination and thirst for 6 weeks. Physical examination was unremarkable, and the patient had no history of trauma or systemic illness. Urine osmolality was markedly low, and MRI of the brain showed absence of the posterior pituitary bright spot and thickening of the infundibulum, suggestive of infundibuloneurohypophysitis. The patient responded well to desmopressin therapy with symptomatic improvement, thus supporting the diagnosis of CDI. This case highlights the importance of considering idiopathic CDI in young adults presenting with unexplained polyuria and polydipsia. Infundibuloneurohypophysitis should be suspected in patients with characteristic MRI findings even in the absence of overt systemic autoimmune disease. A methodical diagnostic approach, including hormone assays, imaging, and therapeutic trials, can enable early diagnosis and effective long-term management.