BackgroundProlactin may exert immunological effects. Over the years, a higher prevalence of autoimmune thyroid diseases (ATD) has been reported in patients with prolactinomas (PRLs) in areas with sufficient iodine intake.PurposeThe aim of our study was to evaluate the prevalence of ATD [Graves’ disease (GD) and chronic autoimmune thyroiditis (AIT)] in a retrospective cohort of Italian patients with PRLs compared to a sex-matched control group, represented by subjects with non-functioning pituitary adenoma (NFPA) or empty sella (ES).Materials and methodsWe enrolled 149 patients (108 F/41 M) with PRLs (110 micro/39 macro) and 143 subjects (100 F/43 M) with NFPA (n = 96, 56 micro/40 macro) or ES (n = 47), with normal serum prolactin. Neck ultrasound and thyroid function tests (anti-thyroid antibodies, TSH, FT3 and FT4) were performed in all patients.ResultsIn PRLs, median serum prolactin was significantly higher (98.3 vs. 8.9 ng/ml, p ≤ 0.0001), while age was lower (34 vs. 46 years, p ≤ 0.001) compared to controls. The prevalence of ATD was 13.4% (20/149) in PRLs (1 GD and 19 AIT) compared to 6.3% (9/143) in the controls (p = 0.042). At the multivariate analysis, serum prolactin was the only independent factor predicting ATD. Thyroid volume (12.5 ± 5.9 ml vs. 12.8 ± 10 ml, p = 0.47) and the presence of uni- or multinodular goiter (29.5% vs. 35%, p = 0.35) did not differ between PRLs and control groups.ConclusionsOur data in an area with mild iodine deficiency confirm a higher prevalence of ATD in patients with prolactinomas.