The background of the study. Many people have high serum titers or concentrations of one or more thyroid antibodies; but whether continued production of these antibodies is dependent on the presence of thyroid tissue is not clear. In this study the effect of complete elimination of thyroid tissue on the production of thyroid antibodies was determined.
How the study was done. The study subjects were 182 patients with papillary or follicular thyroid carcinoma who had high serum titers of thyroid peroxidase or thyroglobulin antibodies. All the patients underwent thyroidectomy, followed by radioiodine and then thyroxine (T4) therapy. Thereafter, the patients were evaluated for recurrent tumor and had measurements of the antibodies annually. Complete thyroid destruction was defined as two consecutive negative whole-body radioiodine scans and a serum thyroglobulin concentration <3 µg/L. Disappearance of serum antibodies was defined as a negative test for the particular antibody during temporary cessation of thyroxine therapy.
The results of the study. At base line, 94 percent of the patients had a high serum titer of antithyroid peroxidase antibodies, and 64 percent had a high serum titer of antithyroglobulin antibodies; 58 percent had a high serum titer of both antibodies.
The average duration of follow-up was 10 years; 59 percent of the patients were followed for 8 years, and 38 percent for 12 years; 4 patients (2 percent) died from thyroid carcinoma. The serum titers of both antibodies decreased gradually in all patients after initial treatment; the median time to disappearance of serum antithyroid peroxidase antibodies was 6.3 years, and the median time to disappearance of serum antithyroglobulin antibodies was 3.0 years. The median time to disappearance of all thyroid tissue was 2.8 years. During follow-up, patients in whom normal or abnormal thyroid tissue was present were more likely to have high serum titers of the antibodies.
The conclusions of the study. In patients with thyroid carcinoma, complete ablation of thyroid tissue results in gradual disappearance of serum antithyroid antibodies.
The original article. Chiovato L, Latrofa F, Braverman LE, Pacini F, Capezzone M, Masserini L, Grasso L, Pinchera A. Disappearance of humoral thyroid autoimmunity after complete removal of thyroid antigens. Ann Intern Med 2003;139:346-51.