The insulin hypoglycaemia and overnight metyrapone tests in the assessmentof the hypothalamic-pituitary adrenal axis following pituitary surgery

OBJECTIVE To compare the insulin hypoglycaemia test with the short overnigh t metyrapone test in the assessment of the hypothalamic-pituitary-adrenal ( HPA) axis posthypophysectomy. DESIGN Prospective comparative study of the insulin hypoglycaemia test and the overnight metyrapone test in 32 patients 4-6 weeks after pituitary surg ery, SUBJECTS Thirty-two patients with known pituitary disease. None with presen t or previous Gushing's syndrome, OUTCOME MEASUREMENTS Maximum serum cortisol achieved during insulin induced hypoglycaemia compared with 0900 hours serum 11-deoxycortisol level follow ing a weight related oral dose of metyrapone at 0000 h, RESULTS One of the 32 patients required further surgery and was studied twi ce after each operation. Thirty-three results are therefore compared, Twent y-six of these had a normal cortisol response of 550 nmol/l or above leadin g to the cessation of replacement hydrocortisone, Six of these 26 patients however, failed the metyrapone test (11-deoxycortisol level less than 200 n mol/l), After 3-40 months (median 20 months) of follow-up off steroid thera py, no patient to date has displayed any clinical evidence of steroid defic iency. Of the seven patients who failed the insulin hypoglycaemia test, six also failed the metyrapone test, CONCLUSIONS The overnight metyrapone test identified more patients with pos sible ACTH deficiency than the insulin hypoglycaemia test, Further follow-u p of these patients is required before a final judgement can be made as to whether more subtle but clinically relevant ACTH deficiency can be detected by the metyrapone test, Our clinical follow-up to date would not support t his.