Ectopic ACTH syndrome associated with large-cell neuroendocrine carcinoma of the lung

Although ectopic adrenocorticotropic hormone (ACTH) syndrome (EAS) is a well-known paraneoplastic phenomenon, an association with large-cell neuroendocrine carcinoma of the lung (LCNEC) has not been reported. We describe a 63-year-old man with metastatic LCNEC to the left temporomandibular joint (TMJ) who presented with progressive muscle weakness and bilateral lower leg edema for 2 weeks. He did not have a typical Cushingoid appearance nor used diuretics. His newly noted hypertension, hypokalemia (plasma potassium (K) concentration 1.8 mEq/L) with renal K wasting, and metabolic alkalosis suggested a state of mineralocorticoid excess. His plasma renin activity and aldosterone concentrations were low, but cortisol and ACTH levels were extremely elevated, consistent with ACTH-dependent Cushing's syndrome. Nonsuppressible plasma cortisol level and normal sella turcica on magnetic resonance imaging pointed to EAS. A strongly positive stain for ACTH from the metastatic left TMJ mass supported LCNEC-related EAS. His hypokalemia and hypertension were controlled with spironolactone and K supplementation. This is the first reported case of EAS in LCNEC and should be kept in mind as a cause of hypokalemia in lung cancer patients.