Correlation between thyroid volume and humoral thyroid autoimmunity after radioiodine therapy in Graves' disease.

BACKGROUND Graves' disease is an autoimmune disorder with the presence of TSH receptor autoantibodies (TRAb). TRAb are produced mainly by lymphocytes infiltrating the thyroid gland. The aim of this study was to investigate the influence of the reduction of thyroid volume (TV) on TRAb level after radioiodine (RAI) administration in a group of patients with Graves' disease. MATERIAL AND METHODS A retrospective chart review of 36 patients with Graves' disease (age range 18-67 yrs; Me 46 yrs; mean age ± SD 43 yrs ± 13.0 yrs) treated with RAI administration (the mean dose of RAI ± SD was 46.1 mCi ± 21.7 mCi ) was performed. Data concerning TV, TRAb, TSH, and fT4 was collected immediately before administration of radioiodine and 18-36 months thereafter. Data was collected before the first administration of RAI and 18-36 months after the last administration of RAI for patients treated with repeated doses of RAI. RESULTS Before treatment, mean male (n = 4) TV was 27.9 ml ± 9.6 ml and mean female (n = 32) TV was 20.6 ml ± 12.7 ml. Mean TV was 2.4 ml ± 1.7 ml(males) and 5.3 ml ± 10.9 ml (females) after therapy. There was an extremely significant difference between mean TV before RAI administration and after 18-36 months. There was an extremely significant difference between the mean serum level of TRAb before and 18-36 months after RAI therapy. No significant correlation between percentage reduction of TV and percentage reduction of serum level of TRAb was found. CONCLUSIONS 1. Decrease of thyroid gland volume after radioiodine therapy is followed by a significant decrease of the level of TRAb after 18-36 months. 2. TRAb concentration is positively correlated with thyroid gland volume. 3. Percentage reduction of TRAb is not correlated with percentage reduction of thyroid volume.