[Cushing syndrome by ectopic ACTH secretion: analysis of the physiopathologic mechanism of hypokalemia. Report of two cases]. / Síndrome de Cushing por secreción ectópica de ACTH: análisis del mecanismo fisiopatológico de la hipokalemia. Comunicación de dos casos.

We report a 42 years old male and a 66 years old female with a Cushing syndrome caused by ectopic ACTH secretion secondary to a carcinoid tumor. These patients had both severe hypokalemia, resistant to medical treatment and that subsided with bilateral adrenalectomy and supplementation with dexametasone. Cushing syndrome caused by ectopic ACTH secretion is characterized by a severe and rapidly evolving hypercortisolism. Hypokalemia is present in 90% of cases and is probably caused by a defect in 11 beta hydroxysteroid dehydrogenase, that limits the binding of cortisol to aldosterone receptor, metabolizing it to cortisone. Therefore, this alteration will increase the mineralocorticoid action of cortisol.