A Stroke of Luck: Central Diabetes Insipidus Unmasked by a Heat Stroke

Diabetes insipidus is a rarely encountered cause of hypernatremia, often presenting a diagnostic and therapeutic dilemma for the encountering physician. Patients are often asymptomatic for a number of years due to compensation of their polyuria with polydipsia, but may have dramatic presentations in situations where they lose access to hydration. Our case is of a 62-year-old woman who was found unconscious with signs and symptoms of a heat stroke, and later was found to have resistant hypernatremia that persisted despite extensive free water supplementation. She had dilute polyuria throughout her hospital course, eventually warranting testing for diabetes insipidus with a vasopressin challenge test. She responded well to therapy with intranasal desmopressin and currently remains asymptomatic. Because our patient was reported to have polyuria and polydipsia for a number of years presumed to be due to underlying diabetes mellitus, it is possible that she had pre-existing central diabetes insipidus that was exacerbated by the lack of access to free water while she was in her intubated and sedated state. Alternatively, she may have also developed new-onset diabetes insipidus due to severe hyperthermia. This case serves to highlight a dramatic presentation of diabetes insipidus, and the importance of careful consideration of its diagnosis in patients with persistent dilute polyuria despite signs of intravascular volume depletion.