Rapid Changes of Prolactinoma Volume after Withdrawal and Reinstitution of Bromocriptine*

Abstract

Medical therapy of prolactinomas with bromo-criptine has been demonstrated to reduce serum PRL levels to normal and also to reduce the size of such tumors. This size reduction may occur very rapidly. It is widely recognized that PRL levels rise again after withdrawal of bromocriptine therapy. We now describe the effects of drug withdrawal and reinstitution on tumor size in two young men harboring large prolactinomas. Bromocriptine had been extremely successful in lowering serum PRL levels by more than 80%, as well as reducing tumor size. After 12 months of therapy bromocriptine was withdrawn. Within 48 h PRL levels had started to rise, reaching 2580 ng/ml at 13 days off therapy and 1040 ng/ml at 4 weeks off therapy in patients 1 and 2, respectively. At 13 days bitemporal hemianopsia recurred in patient 1, and this was associated with radiographic demonstration of expansion in the pituitary mass from a partially empty pituitary fossa to a large 12-mm suprasellar extension. The second patient remained asymptomatic, but his tumor also reexpanded after withdrawal of bromocriptine. Bromocriptine (2.5 mg, three times daily) was reinstituted in both cases and resulted in a rapid fall i n serum PRL and reduction of tumor size in both patients; patient 1 had improvement in headaches at 24 h, vision at 3 days, and restoration of visual fields to normal at 6 months. Bromocriptine therapy is successful in reducing tumor size and lowering PRL levels with return of normal gonadal function. Patients with large prolactinomas treated with bromocriptine alone should be withdrawn from therapy very cautiously to avoid reexpansion of their tumor.