Isolated ACTH deficiency (IAD) is a rare disorder, characterized by secondary
adrenal insufficiency (AI) with low or absent
cortisol production, normal secretion of
pituitary hormones other than
ACTH and the absence of structural pituitary defects. In adults, IAD may appear after a traumatic injury or a
lymphocytic hypophysitis, the latter possibly due to autoimmune etiology. Conversely, a genetic origin may come into play in neonatal or childhood IAD. Patients with IAD usually fare relatively well during unstressed periods until intervening events spark off an acute adrenal crisis presenting with non specific symptoms, such as
asthenia,
anorexia, unintentional
weight loss and tendency towards
hypoglycemia. Blood chemistry may reveal mild
hypoglycemia,
hyponatremia and normal-high
potassium levels, mild
anemia,
lymphocytosis and
eosinophilia. Morning serum
cortisol below 3 microg/dl are virtually diagnostic for
adrenal insufficiency. whereas
cortisol values comprised between 5-18 microg/dl require additional investigations:
insulin tolerance test (ITT) is considered the gold standard but-when contraindicated-high or low dose-
ACTH stimulation test with serum
cortisol determination provides a viable alternative. Plasma
ACTH concentration and prolonged
ACTH infusion test are useful in differential diagnosis between primary and secondary
adrenal insufficiency. For some patients with mild, near-to-
asymptomatic disease,
glucocorticoid replacement
therapy may not be required except during stressful events; for symptomatic patients, replacement doses i.e., mean daily dose 20 mg (0.30 mg/kg)
hydrocortisone or 25 mg (0.35 mg/kg)
cortisone acetate, are usually sufficient. Administration of
mineralocorticoids is generally not necessary as their production is maintained.