Plurihormonal pituitary adenomas have been described in medical literature as functional tumours that secrete two or more pituitary hormones. Most of these plurihormonal adenomas are associated with acromegaly. Bihormonal secretion of ACTH-Prolactin are very rare with only 6 other published case reports.
A 23 year old man presented with florid Cushing's syndrome and was found to have high ACTH (40pmol/L; reference range 2-11pmol/L) and very high plasma prolactin (40724mIU/L; reference range 70-300mIU/L). Pituitary MRI showed a large invasive macroadenoma. Low dose cabergoline promptly suppressed both ACTH and prolactin levels within 2 weeks, including unexpected clinical and biochemical hypocortisolism requiring hydrocortisone replacement. Clinical and biochemical remission of his Cushing's syndrome along with significant shrinkage of his macroadenoma has been maintained for six months on cabergoline 0.5mg twice weekly. The pituitary tumour shrinkage as well as the brisk fall in serum prolactin in response to low dose cabergoline has been regularly observed in patients with macroprolactinomas but the concurrent fall in plasma ACTH levels and hypocortisolism was a pleasant surprise. We assume that he has a single bihormonal adenoma that is enriched with dopamine 2 receptors.
Cabergoline is the established first line therapy for prolactinomas as they are enriched with dopamine 2 receptors . In the treatment of acromegaly, cabergoline is considered a second line therapy. The role of cabergoline in the treatment of non-functioning pituitary adneomas and Cushing's disease remain controversial although these tumours may also express dopamine 2 receptors. A review of cabergoline treatment of 88 patients with Cushing's disease reported control of disease in 31% of patients, but escape occured in one third.
In our patient, we were able to demonstrate sustained response for six months of therapy to date. The most unusual feature was the rapid remission fo Cushing's disease to the extent of developing hypocortisolism in the absence of pituitary infarction or apoplexy.