Hyperprolactinaemia in hypothyroidism: clinical significance and impact of TSH normalization

Menstrual irregularities in hypothyroidism have been reported to occur less frequently than previously described. We therefore studied the influence of serum PRL in patients with newly diagnosed subclinical and overt hypothyroidism and in hyperprolactinaemic patients treated with T4 to distinguish the impact of hypothyroidism from that of confounding drugs on hyperprolactinaemia and menstrual irregularities.

PRL was determined in 1003 consecutive hypothyroid patients (TSH > 4.0 mU/l) at referral, and after TSH normalization in 84 (8%) initially hyperprolactinaemic (female, > 480 mU/l; male, > 432 mU/l) subjects. Medical history (psychotropic drugs and oestrogens) and menstrual patterns were assessed at referral and after 8 +/- 5 (mean +/- SD) months of T4 therapy. Pituitary magnetic resonance imaging (MRI) was offered to patients with persistently elevated PRL.

Menstrual disturbancies (oligomenorrhoea/secondary amenorrhoea, O/A) were not more common (P = NS) in hyper- than in normoprolactinaemic women (26% and 16%, respectively). We observed no galactorrhoea and no correlation between PRL and TSH or O/A except in pregnant or lactating women (N = 11). Oestrogens or antidepressants (including selective serotonin reuptake inhibitors) did not cause hyperprolactinaemia but antipsychotic drugs did. PRL decreased with T4 therapy (P < 0.01) in patients not using confounding drugs (from 720 +/- 288 to 360 +/- 192 mU/l) but menstrual irregularities persisted. PRL remained unchanged in patients receiving antipsychotic treatment. PRL was also unchanged in patients with pituitary abnormalities (seven micro-, one macroadenoma).

Hyperprolactinaemia was not an important feature in patients with newly diagnosed hypothyroidism. Neuroleptic drugs may cause persisting hyperprolactinaemia after TSH normalization. In addition, menstrual disturbancies do not relate to hyperprolactinaemia in hypothyroidism.