The metyrapone test, based on the urinary steroid or ACTH response to this 11b-hydroxylase enzyme blocker, has now been shown to be of no diagnostic value. Abnormal, high molecular- weight forms of ACTH (ΓÇÿbig ACTHΓÇÖ) are frequently seen with ectopic sources and, in rare instances, when pituitary-dependent Cushing's disease is caused by a large tumour.
