Ectopic Cushing's Syndrome as the First Presenting Sign of Small Cell Lung Carcinoma

A 67-year-old man with a history of hypertension, hyperlipidemia, coronary artery disease, and former smoking presented with fatigue, lower extremity edema, and a new tremor over the course of one month. Workup was notable for hypokalemia, metabolic alkalosis, and extremely elevated adrenocorticotropic hormone (ACTH) and cortisol levels. He was ultimately diagnosed with ectopic Cushing's syndrome (CS) secondary to new metastatic small cell lung carcinoma. About 5-10% of CS cases are caused by ectopic ACTH production. The most commonly implicated malignancies are small cell lung cancer (SCLC) and neuroendocrine tumors, with SCLC accounting for up to three-fourths of cases. ACTH production is a poor prognostic sign in SCLC, associated with more extensive disease and decreased response to first-line treatment. Tumor-associated ACTH production is often so rapid that patients do not have time to develop classic Cushingoid physical exam findings, instead presenting with acute-onset hyperglycemia, pseudohyperaldosteronism, and generalized weakness. Prompt diagnosis and treatment are essential to improve outcomes.