Failure of the short ACTH test to unequivocally diagnose long-standing symptomatic secondary hypoadrenalism

Recent guidelines propose that secondary hypoadrenalism can be reliably diagnosed, in the absence of acute ACTH deficiency or glucocorticoid use, by means of the short ACTH test (Synacthen). We report a patient who maintained a normal response to exogenous ACTH stimulation despite symptomatic chronic ACTH deficiency proven by the insulin tolerance and overnight metyrapone tests. It is suggested that partial ACTH deficiency may prevent involution of the adrenal cortex and preserve the cortisol response to ACTH stimulation. A normal cortisol response in the short ACTH test does not therefore exclude the possibility of clinically relevant ACTH deficiency.