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Abstract

Diabetes insipidus (DI) is a disorder characterised by the passage of excess amounts of dilute urine. In central diabetes insipidus, there is a deficiency of antidiuretic hormone (ADH) and in nephrogenic diabetes insipidus, there is decreased response of the kidneys to ADH. In addition to various congenital and acquired causes, several drugs have been implicated in the etiology of DI. Lithium and clozapine are the most common psychotropic drugs shown to induce drug-induced DI. Olanzapine-induced DI is relatively rare and has been reported to occur primarily in the context of overdose. Here, we describe the clinical manifestations and outcome of a patient who was diagnosed with alcohol-induced psychosis and later developed olanzapine-induced DI at a therapeutic dose. After initiation of olanzapine and gradual titration up to 10mg, the patient reported polyuria, polydipsia, and nocturia. Further evaluation revealed low urine osmolality and normal plasma osmolality favouring a diagnosis of diabetes insipidus. The symptoms resolved within a few days of discontinuation of olanzapine without any other specific treatment. A score of 7 was obtained on the Naranjo adverse drug reaction probability scale indicating that olanzapine was the probable cause of DI in the present patient. As evident practising psychiatrists should be aware of the possibility of drug-induced DI as a possible differential diagnosis to primary polydipsia in psychotic patients. Awareness of and familiarity with diagnostic algorithms is essential for rational investigations and identification of the underlying cause.