Factors determining the remission of microprolactinomas after dopamine agonist withdrawal.

BACKGROUND: Withdrawal of dopamine agonist (DA) therapy in the management of microprolactinoma is common practice, but it is unclear which patients are likely to attain long-term remission.

OBJECTIVE: To identify predictive factors for long-term remission.

DESIGN: Prospective cohort study.

PATIENTS: Forty subjects (39 female, aged 24-60 years) with microprolactinoma; all had been normoprolactinaemic on DA therapy for at least 2 years [mean duration of therapy 9 years (range 2-27)].

MEASUREMENTS: A pituitary magnetic resonance imaging (MRI) was performed on 36 (90%) subjects before DA withdrawal. Relapse was defined as prolactin greater than 480 mIU/l (22.8 microg/l) on two occasions.

RESULTS: Nine out of 40 (22.5%) subjects were normoprolactinaemic 12 months after DA withdrawal. Amongst the relapse group, 24 of 31 subjects (79.4%) had already relapsed at 3 months. Normalization of MRI prior to DA withdrawal (P = 0.0006) and longer duration of DA treatment (P = 0.032) were significant predictors of remission. Age, pre-treatment prolactin, nadir prolactin, previous failure of DA withdrawal, pregnancy, dose and type of DA were not significant predictors of remission. The nine patients who were in remission at 12 months were then followed up for 58.0 +/- 5.8 months; all remained in remission.

CONCLUSIONS: As many as 22.5% of subjects with microprolactinoma remained normoprolactinaemic 12 months after DA withdrawal and these subjects stayed in remission for up to 5 years. Significant predictive factors were normalization of MRI prior to discontinuation, and duration of DA treatment. Our findings support intermittent DA withdrawal after a period of normoprolactinaemia, particularly where MRI appearances have normalized.