Pituitary enlargement and hyperprolactinaemia due to primary hypothyroidism: errors and delays in diagnosis.

Two young women with pituitary gland enlargement and hyperprolactinaemia were referred for pituitary surgery. Both had received bromocriptine (one patient for 13 years) for presumed prolactinoma. Mild clinical signs of hypothyroidism were present and endocrine tests revealed primary autoimmune thyroid failure. Following thyroxine replacement treatment, the pituitary enlargement and hyperprolactinaemia completely resolved. In both patients the hyperprolactinaemia was relatively mild and menorrhagia had been present for many years. A third patient, a 61-year-old man presenting with bitemporal hemianopia due to pituitary enlargement underwent transphenoidal pituitary surgery. The results of thyroid function tests on admission were not available until after surgery. Although the patient was clinically euthyroid, these revealed primary hypothyroidism and his considerable pituitary enlargement may also have been secondary to thyroid failure. Urgent thyroid function tests should be performed in all patients with pituitary enlargement prior to surgery to exclude hypothyroid induced pituitary swelling.