The higher incidence of autoimmune thyroid disease in prolactinomas than in somatotrophinomas.

Objective: Many studies have shown that prolactin (PRL) plays an important role in autoimmune diseases. The aim of this study was to compare the current frequency of autoimmune thyroid disease (ATD) in prolactinomas with another type of functional pituitary adenoma (FPA), somatotrophinoma. Another aim of the study was to evaluate possible factors related to thyroid autoimmunity and the process of ATD in FPAs.

Methods: We retrospectively evaluated the presence of thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) and thyroid morphologic findings in our patients with FPA (78 with acromegaly and 83 with prolactinoma). The relationship of autoantibody positivity with baseline PRL levels, activity of acromegaly, and treatment of dopamine agonists (DA) and hypogonadism was also assessed. Patients with ATD and hypothyroidism due to autoimmune thyroiditis were also evaluated.

Results: ATD (Hashimoto's thyroiditis) was detected more frequently in patients with prolactinoma than in patients with acromegaly (33% and 17%, respectively; p=0.01). Thyroid autoantibody positivity was found more frequently in females in the whole group (p=0.02) and in the acromegaly group (p=0.008). There was no difference according to sex among the patients with prolactinoma (p=0.800). ATD was found not to be related with baseline PRL levels, treatment of DA, and presence of hypogonadism (p=0.232, p=0.435, p=0.464, respectively) in the prolactinoma group, and activity of acromegaly, presence of hypogonadism in the acromegaly group (p=0.753, p=0.654, respectively). Autoimmune hypothyroidism was more frequent in the prolactinoma group than in the acromegaly group among patients with thyroid autoantibody positivity (p=0.004).

Conclusion: Thyroid autoantibodies should be evaluated both at the time of diagnosis and during the course of treatment in patients with prolactinoma, and thyroid function tests should be closely monitored in patients with autoantibody positivity.