Corticotrophic macroadenoma of the pituitary associated with hypoadrenalism

A 60-year-old man underwent transfrontal surgery for a macroadenoma of the pituitary which presented with chiasmal compression, and immunohistochemical examination of the resected specimen revealed a corticotrophic tumour. Despite subsequent external irradiation, he was left with a large tumour remnant, which continued to grow. There were no clinical signs of Cushing's syndrome either before or after surgery and 24 h urine excretion of cortisol was not elevated. Plasma ACTH concentrations were marginally raised. However, there was loss of circadian variation in serum cortisol concentrations and administration of high-dose oral dexamethasone was followed by a marked and reproducible rise in both ACTH and cortisol. Two years later he developed symptoms and signs of hypoadrenalism and urine cortisol excretion was low, even though the paradoxical response to dexamethasone was preserved. Treatment with 0.5 mg dexamethasone each day was associated with partial resolution of his symptoms and urine cortisol concentration rose into the normal range. This treatment was maintained until his death in hospital in April 1988. The possible mechanism underlying the association between a corticotrophic tumour and hypoadrenalism are discussed.