RESUMO
We present a case of refractory hypernatremia in a patient with elevated adrenocorticotropic hormone (ACTH) and hypercortisolism. Cortisol's effect in tissues results in various outcomes, from maintaining blood pressure to increasing serum glucose levels. In addition, cortisol, cortisone, and aldosterone activate mineralocorticoid receptors with the same affinity; therefore, the activation of mineralocorticoid receptors by elevated cortisol levels leads to increased sodium reabsorption, increased potassium secretion, and metabolic alkalosis. Hypernatremia in our patient was initially refractory to fluid replacement but was eventually corrected with intravenous fluid and desmopressin. Overall, we suggest that hypercortisolism should be considered a differential diagnosis in hypernatremia refractory to fluids replacement.