[From syndrome of inappropriate antidiuretic hormone secretion deficiency to excess - Challenges and solutions in a...

Introduction: the sequential transition from central diabetes insipidus (CDI) to the syndrome of inappropriate antidiuretic hormone secretion (SIADH) is an exceptionally rare condition and represents a major diagnostic and therapeutic challenge. Case report: we report the case of a 47-year-old man with Burkitt lymphoma involving the hypothalamic-pituitary region who initially presented with polyuria, polydipsia, and hypernatremia. CDI was confirmed by biochemical findings and a positive response to desmopressin. Following desmopressin treatment and intensive chemotherapy, rapid tumor regression and partial recovery of neurohypophyseal function were observed. During follow-up, the patient developed persistent euvolemic hyponatremia with low plasma osmolality, inappropriately concentrated urine, and elevated urinary sodium. After excluding adrenal insufficiency, hypothyroidism, desmopressin overtreatment, and other secondary causes, SIADH was diagnose. Discussion: this case highlights the rare sequential transition from ADH deficiency to ADH excess caused by the same hypothalamic-pituitary disease and supports oral urea as an effective, safe, and cost-effective therapeutic option for chronic SIADH.