Thyroid Autoimmunity and Subclinical Hypothyroidism in Prolactinoma: A Case Control Study.

Background: This study was aimed at determining the frequency of thyroid autoimmunity and subclinical hypothyroidism in patients with hyperprolactinemia due to prolactinoma compared to well-matched healthy controls. Methods: This was a cross-sectional study wherein 78 treatment naïve prolactinoma patients and ninety-two healthy control subjects were recruited. Serum prolactin (PRL), thyroid-stimulating hormone (TSH), total thyroxine (T4), circulating anti-thyroid peroxidase (anti-TPO), and anti-thyroglobulin (anti-Tg) antibody levels were measured in all study subjects. Progression of the antibody-positive population to subclinical hypothyroidism was determined. Results: The median PRL level among patients was 166 ng/ml (IQR 85-467) compared to 11.4 ng/ml (IQR 8.5-15.9) in controls (P < 0.001). There was no significant difference in levels of T4 (P = 0.83) and TSH (P = 0.82) between the cases and controls. Overall, 25% of patients had the presence of anti-thyroid antibodies as compared to 20% of controls (P = 0.56). SCH was more common in antibody-positive hyperprolactinemia subjects compared with antibody-positive controls. Conclusion: We did not find an increased prevalence of thyroid autoimmunity among untreated prolactinoma patients compared to healthy controls. At the same time, subclinical hypothyroidism was more common in thyroid antibody-positive patients with hyperprolactinemia than positive controls.