Probable ACTH-secreting pituitary tumour in association with Addison's disease

A 61 year old Japanese man with a diagnosis of Addison's disease was admitted to Kyushu University Hospital for further investigation of high ACTH levels and hyperpigmentation which 37.5 mg of cortisone acetate failed to alleviate. The basal level of plasma ACTH was 700-1000 pg/ml, and following 25-37.5 mg cortisone acetate or 1 mg dexamethasone the levels were 300-600 pg/ml. The general pigmentation showed little improvement with such medication. Radiographic studies revealed a double floor of the sella turcica and cisternal herniation. These observations suggested the existence of a pituitary ACTH-secreting tumour. Plasma ACTH showed a circadian rhythm ranging from 440 to 1570 pg/ml and it was not suppressed to a normal range by oral administration of dexamethasone, 8 mg/day or by continuous infusion of dexamethasone, 1.25 mg/h for 2 h. Plasma ACTH responses of 80% above basal level to lysine-vasopressin (LVP), and 12% above basal to synthetic ovine corticotrophin releasing factor (CRF) were observed. FK 33-824, a methionine-enkephalin analogue, suppressed plasma ACTH to 85% of basal level, while bromocriptine (CB-154) caused no significant change. These findings led to a diagnosis of pituitary ACTH-secreting adenoma (corticotropinoma) in association with Addison's disease. The persistent circadian rhythm of plasma ACTH suggested that this adenoma may not be completely free from regulation by the central nervous system. This case may be clinically significant for investigation of the pathogenesis of pituitary adenoma, particularly in Nelson's syndrome.