Bendamustine-induced nephrogenic diabetes insipidus

A 59-year-old man presented with polyuria and polydipsia immediately following his sixth cycle of rituximab and bendamustine for chronic lymphocytic leukemia. He initially compensated by increasing his oral fluid intake at home, but later developed septic shock and was admitted with orders to be kept nil per os (NPO). This prompted an episode of acute hypernatremia during which he exhibited continued polyuria with inappropriately dilute urine. Desmopressin challenge yielded no response in the urine osmolality, indicating a nephrogenic source of his diabetes insipidus (DI). He had no known exposure to other causative agents and had demonstrated a robust response to chemotherapy. The patient became eunatremic once oral intake was resumed and his infection was treated. Two months after presentation, he remained symptomatic. A trial with hydrochlorothiazide resulted in a significant increase in urine osmolality and subsequent decrease in urine output. To our knowledge, this is the first case of nephrogenic diabetes insipidus after rituximab and bendamustine exposure. We propose that bendamustine, similar to the alkylating agent ifosfamide, is toxic to the glomerulus and proximal tubule cells and is the most likely cause of the patient's nephrogenic DI.