Refractory hyponatremia secondary to idiopathic, isolated aldosterone deficiency

Hypoaldosteronism is an uncommon, but well-recognized cause of hyponatremia. Hypoaldosteronism is often attributed to renin deficiency or primary adrenal insufficiency. Here, we present the case of a patient with recurrent, refractory hyponatremia due to hypoaldosteronism with normal serum renin activity and cortisol levels. He was started on fludrocortisone with normalization of electrolytes. This is a highly unusual case of hypoaldosteronism without perturbation to the renin-angiotensin system or adrenal insufficiency and serves as an important reminder that aldosterone deficiency should be considered as a potential cause of hyponatremia independent of renin activity or other markers of adrenal function.