Ectopic ACTH syndrome and severe hypokalaemia

Cushing's syndrome is rare and remains a challenge to diagnose. Particularly difficult are the differentiation between Cushing's syndrome and Pseudo-Cushing's states and between the two forms of ACTH dependent Cushing's: Cushing's disease and ectopic ACTH syndrome. We report the case of a patient diagnosed with a metastatic small cells lung carcinoma associated with ectopic ACTH-syndrome. Hypokalaemia was a clue to diagnosis. We focus on critical questions addressing diagnosis and differential diagnosis of Cushing's syndrome and we explain the mechanism of hypokalaemia.