[Clinical evaluations of subtotal thyroidectomy for Graves' disease]

An attempt was made to determine the clinical evaluation of subtotal thyroidectomy in 58 patients with Graves' disease. The weight of the remnant thyroid gland was measured during the operations. Postoperative thyroid volume was measured by ultrasonography (thyroid volume = pi abc/6; a is length, b width, and c thickness). Postoperative thyroid function including serum TSH, free triiodothyronine (FT3), free thyroxine (FT4), thyroglobulin (Tg), TSH receptor antibodies (TRAb), and antimicrosomal antibodies (MCHA) was examined. Fifty-eight patients were divided into the three groups, according to postoperative thyroid function; 39 (67.2%) in remission, 7 (12.1%) with relapse and 12 (20.7%) in a hypothyroid state. Postoperative thyroid volume in patients with relapse was significantly (p < 0.05) greater than that in patients in remission and in a hypothyroid state. Remnant thyroid weight in patients with relapse was significantly (p < 0.05) heavier than that in patients in remission and in a hypothyroid state. However, there was no significant difference in an estimated total thyroid weight among the three groups. A significant correlation was noted between the remnant thyroid weight and the postoperative thyroid volume (R = 0.58, p < 0.001). On the other hand, there was a significant correlation between serum Tg level and the postoperative thyroid volume (R = 0.45, p < 0.01). Serum level of Tg in patients with relapse was significantly (p < 0.05) higher than that in patients in remission and in a hypothyroid state. The prevalence of negative MCHA in patients in remission appeared relatively higher than that in patients with relapse and in a hypothyroid state. In patients with a remnant thyroid weight of less than 4.0 g, there was no recurrence following subtotal thyroidectomy, but a higher prevalence of hypothyroid state (43%) was observed compared to those of larger remnant thyroid weight. In patients with a remnant thyroid weight of 4.0 to 6.0 g, there was a lower prevalence of recurrence (5.9%) compared to those with a larger remnant thyroid weight, while most patients showed remission (73.5%). On the other hand, the highest prevalence of recurrence (23.5%) was obtained in patients with a remnant thyroid weight of more than 6.0 g. These observations indicate that postopertive thyroid state does not depend upon an estimated total thyroid weight, but depends upon a remnant thyroid weight. In addition, a remnant thyroid weight is closely associated with thyroid volume measured by ultrasonography after subtotal thyroidectomy, which reflected the serum level of Tg.