A 54-year-old man with
type 2 diabetes was referred to our hospital for endocrine evaluation of
acromegaly. Physical examination showed typical acromegalic features without Cushingoid features. Magnetic resonance imaging of the brain revealed the presence of a pituitary macroadenoma. Basal plasma levels of GH and
insulin-like growth factor-I under fasting
hyperglycemia (202 mg/dl) were markedly elevated. Plasma GH levels paradoxically increased after stimulation with TRH and
LH-RH, and decreased after
bromocriptine and
octreotide administration. Endocrine examination of the hypothalamo-pituitary-adrenal (HPA) axis showed a lack of circadian rhythm of
ACTH and
cortisol, non-suppressibility to low-dose (1 mg), but suppressibility to high-dose (8 mg)
dexamethasone, and normal response to CRH stimulation. The
tumor resected by transsphenoidal surgery was histopathologically consistent with the diagnosis of
eosinophilic adenoma: positive immunoreactivities of GH, PRL and
ACTH were demonstrated, but negative immunoreactivities of
prohormone convertase (PC) 1/3 by immunohistochemical method. After surgery, plasma GH and
IGF-I levels decreased along with normalization of HPA axis. Metabolic co-morbidities such as diabetes and
hypertension disappeared after removal of the
pituitary tumor. This is a very rare case of GH-producing
pituitary adenoma causing typical
acromegaly with concomitant production of
ACTH causing subclinical
Cushing's disease.