Prevalence and functional significance of antipituitary antibodies in patients with autoimmune and non-autoimmune thyroid diseases.

BACKGROUND Circulating antipituitary antibodies (APA) are markers of autoimmune hypophysitis, which may cause deficient pituitary function. The prevalence of APA in autoimmune thyroid disorders (AITD) is uncertain. OBJECTIVES The aims of this study were 1) to evaluate APA prevalence in a large series of patients with AITD and non-AITD and 2) to investigate the functional significance of APA by assessing pituitary function in APA-positive patients. DESIGN AND SETTING We conducted a health survey on consecutive AITD and non-AITD patients at a tertiary referral center (Department of Endocrinology, Pisa). PATIENTS Subjects, including 1290 consecutive patients with thyroid disorders (961 AITD and 329 non-AITD) and 135 controls, were enrolled in the study. METHODS APA (indirect immunofluorescence), free T(4), free T(3), TSH, and organ-specific autoantibodies were assayed in all patients. Functional pituitary evaluation was performed in most APA-positive patients. RESULTS APA frequency was higher in AITD (11.4%) than in non-AITD (0.9%; P < 0.0001) patients; all control subjects had negative APA tests. APA were more frequently found in Hashimoto's thyroiditis (13%) than in Graves' disease (7.1%; P = 0.05). Of 110 APA-positive AITD patients, 20 (18.2%) had autoimmune polyglandular syndrome, whereas 90 (81.8%) had apparently isolated AITD. APA positivity increased percentage of autoimmune polyglandular syndrome in our series from 10.4 to 13.5%. Of 110 APA-positive patients, 102 were submitted to dynamic testing for functional pituitary assessment; 36 patients (35.2%) had mild or severe GH deficiency (GHD). No additional anterior pituitary hormone deficiencies were found; one patient had central diabetes insipidus. Pituitary abnormalities at magnetic resonance imaging were found in most APA-positive GHD patients. CONCLUSIONS APA are frequently present in patients with AITD. Patients should be tested for APA because positive tests are associated with GHD.