Life-Threatening Hypernatremia In A Case Of Diabetes Insipidus/Panhypopituitarism

Abstract

Management of diabetes insipidus (DI) accompanied by panhypopituitarism requires understanding of the relationships between ADH and thyroid/glucocorticoid tone. Low thyroid/glucocorticoid tone decreases free water clearance which protects against DI and may lead to hyponatremia while high thyroid/glucocorticoid tone may unmask DI and facilitate hypernatremia. A 31 year-old man with DI/panhypopituitarism was stable until his levothyroxine was incorrectly lowered based on TSH levels. He became hypothyroid and was hospitalized 3 times over 1 month for recurring altered mental status and mild hyponatremia. DDAVP was repeatedly held with rapid onset of polyuria resulting severe hypernatremia. On the last admission, he presented with altered mental status from sepsis. Serum sodium was 135 mmol/l. He was made NPO and treated with stress dose hydrocortisone and fludrocortisone. DDAVP was held for the mild hyponatremia. Serum sodium rapidly elevated to 168 mmol/l after only 12 hours. DDAVP was restarted with liberalization of diet to unlimited free water access causing rapid downward sodium correction. Hypernatremia almost always results from iatrogenic causes. In our case, holding DDAVP for hyponatremia resulted in rapid onset of hypernatremia and volume depletion. Stress dose glucocorticoids further unmasked DI. Thirst and free access to water which typically protects patients with un-replaced DI were not operational due to his NPO status which contributed to the rapid rise in serum sodium. Water balance is controlled by thyroid, glucocorticoid, and principally ADH working at the renal effector level while the RAAS principally controls sodium balance. Together these hormones tightly regulate serum sodium concentration. Managing hospitalized patients with DI/panhypopituitarism requires knowledge of the intricate interplay between ADH and thyroid/glucocorticoid tone to minimize the risk for dangerous sodium fluctuations. It is usually better to err on the side of mild hyponatremia than holding DDAVP in these complex patients which can lead to life threatening hypernatremia.