Autoimmune thyroid disease and antiphospholipid antibodies.

Abstract

Autoimmune thyroid disease (ATD) is associated with circulating autoantibodies reactive with epitopes on thyroid tissue and that are thought to be pathogenic in the development of these diseases. Antiphospholipid antibodies (APLA) are a family of immunoglobulins that recognize a variety of plasma proteins in association with anionic phospholipids. These antibodies may lead to a number of clinical syndromes including venous and arterial thromboses, thrombocytopaenia, and recurrent fetal loss. We have studied the prevalence of APLA in patients with ATD and have determined the prevalence of the APLA syndrome among APLA-positive patients. The study was a retrospective survey of patients with autoimmune thyroid disease attending the endocrinology clinic of a tertiary care academic hospital. One hundred and thirty patients with autoimmune thyroid disease from the endocrinology clinic at our hospital were studied. 84% had chronic thyroiditis and 16% had Graves' disease. Free T4 and thyroid stimulating hormone (TSH) levels, antimicrosomal and antithyroglobulin antibodies, and an antiphospholipid antibody test were performed on all subjects. 43% of patients with chronic thyroiditis and 43% of patients with Graves' disease were APLA positive, with an overall rate of 43% APLA positivity among patients with ATD. Of the 56 patients that were APLA positive, forty-eight (86%) had APLA of the IgG subtype, four (7%) had IgM antibodies, and nine (16%) had both IgG and IgM antibodies. None of the patients had clinical evidence of the APLA syndrome. We conclude that the prevalence of APLA in ATD is increased compared to healthy individuals but that this is likely to be an epiphenomenon. However, prolonged follow up is necessary in order to determine the true clinical significance of these antibodies in ATD patients.