Hypertension and severe hypokalaemia associated with ectopic ACTH production

Ectopic adrenocorticotropic hormone (ACTH) secretion represents 5%-10% of cases of Cushing's syndrome (CS), and approximately 50%-60% of these arise from neuroendocrine lung tumours, including small-cell lung cancer (SCLC). We report a 42-year-old man admitted with hypertension, metabolic alkalosis and severe hypokalaemia. On physical examination, centripetal obesity with 'moon face' and 'buffalo's hump' were identified, and wheezing on left lung was heard. A markedly elevated serum cortisol, ACTH and urine free cortisol production supported the diagnosis of CS. Chest CT showed a left hilar mass with metastasis to the liver, adrenal glands and lymph nodes. Bronchoscopy identified bronchial infiltration by SCLC. Treatment with metyrapone and chemotherapy was started. Despite initial improvement, progressive clinical deterioration occurred, culminating in death 1 year after diagnosis. Ectopic ACTH secretion is uncommon but should be suspected in patients with severe hypokalaemia, hypertension and metabolic alkalosis, especially in the context of lung cancer.