A fall in serum prolactin level after a 2 hour rest predicts a normal MRI in patients using dopamine antagonist treatment

Introduction: Hyperprolactinaemia associated with antipsychotic drug use is a commonly encountered clinical problem, yet no decision-making tools exist to guide whether to scan the pituitary gland. Methods: A 10-year data series was reviewed of 246 patients who were evaluated for prolactin excess with a cannulated prolactin study. All patients had a prolactin drawn immediately following the insertion of a forearm cannula (P1) and a second sample drawn after 120 min bed rest (P2). Comparison was made between patients with a confirmed microprolactinoma (galactorhoea and/or oligomenorrohea with resting hyperprolactinaemia and microadenoma on MRI) against those on dopamine antagonists as well as normal controls. The presence of macroprolactin was excluded in all samples. Results: Sixteen patients out of 246 were on dopamine antagonists. In eight patients the prolactin normalised following discontinuation of the drug for at least 3 weeks. Conclusion: In our series, prolactin normalised after 2 weeks of cessation of dopamine antagonists, when treatment could safely be discontinued. A fall after 2 h rest predicted a normal MRI in patients continuing on dopamine antagonists