Lalloo, 50 years old, a chronic smoker, presents with history of hemoptysis. He was having truncal obesity and hypeension. He had an elevated ACTH level which was not suppressible with high dose dexamethasone. What would be the most probable diagnosis:

Answer is D (Ectopic ACTH producing lung cancer) Truncal obesity, hypeension and elevated ACTH levels suggest a diagnosis of Cushing's syndrome. Elevated ACTH level not suppressible by high dose Dexamethasone indicate the diagnosis of Cushing's syndrome due to Ectopic ACTH production.