A possible ACTH secreting tumour of the pituitary developing in a conventionally treated case of Addison's disease.

A patient with Addison's disease, treated with conventional corticosteroid therapy, developed endocrine and radiological features suggestive of an ACTH secreting pituitary tumour. The negative feedback control of ACTH secretion by the inhibitory effect of hydrocortisone was shown to be preserved although attenuated. Retiming and alteration of corticosteroid therapy reinforced this feedback control, without the need for supraphysiological amounts of steroid, and resulted in the regression of the endocrine disorder.