Effect of dopamine agonist withdrawal after long-term therapy in prolactinomas. Studies with high-definition computerised tomography.

The clinical, radiological, and biochemical effects of dopamine agonist withdrawal after long-term treatment were investigated in seven women and eight men who had been treated for prolactinomas for 1.5 to 7 (mean 3.7) years. Before treatment, serum prolactin concentrations were 1473 to 115 000 mU/l, all patients had abnormal radiological findings, and six had suprasellar extensions of pituitary tumours. Treatment with either bromocriptine or pergolide relieved symptoms and suppressed prolactin secretion in most patients. The size of the residual tumour was defined by doing fourth generation computerised tomographic scans immediately before termination of therapy, and evidence of tumour re-expansion was sought on scans repeated 5-39 weeks later. After discontinuation of treatment, symptoms recurred in 13 of 15 patients and hyper-prolactinaemia redeveloped in 14. Other pituitary function tests remained unchanged or improved. In 13 of 15 patients tumour or gland size did not change after withdrawal of treatment. One man had a marginal increase in tumour size, while in another the pituitary tumour shrank. Thus, although cessation of long-term dopamine agonist therapy leads to recurrence of symptoms and hyperprolactinaemia, rapid tumour regrowth is uncommon and of small extent, and other pituitary function is not altered in the short term.