ABSTRACT
Prolactin (PRL) is a hormone characterized by its immunomodulatory properties. The aim of this study was to evaluate the prevalence of thyroid autoimmunity in patients with prolactinoma. Seventy-seven patients and 56 healthy individuals in the control group, sex and age matched, had their serum PRL, free tetraiodothyronine, thyroid-stimulating hormone and anti-thyroid peroxidase (anti-TPO) levels measured. The prevalence of anti-TPO for patients was 13% and 8.9% for control group (p = 0.58). The analysis of subgroups of patients, divided in accordance with tumor size at diagnosis, showed no significant difference in the frequency of anti-TPO. However, when they were divided in accordance with the prolactin levels at the moment of the study, 18.8% with valid hyperprolactinemia and 3.4% without hyperprolactinemia had positive autoantibody (p = 0.07). In conclusion, there was no greater prevalence of thyroid autoimmunity in patients with prolactinoma. Nevertheless, those with valid hyperprolactinemia showed a greater tendency for positive autoantibody anti-TPO