Thyroid volume reduction in patients with thyroid stimulation-blocking antibody who transitioned from Graves' hyperthyroidism to hypothyroidism: a single-center retrospective study.

Some patients with Graves' disease (GD) develop hypothyroidism after antithyroid drug (ATD) treatment and are found to be positive for thyroid stimulation-blocking antibody (TSBAb). However, thyroid volume (TV) changes throughout this process remain unclear. Therefore, we aimed to quantify TV changes before and after hypothyroidism onset in patients with GD harboring TSBAb and compare them with those in patients with GD who developed hypothyroidism without TSBAb or achieved remission with ATD. This retrospective study evaluated TV changes using ultrasonography in three groups: 10 patients with GD who developed hypothyroidism with TSBAb (TSBAb(+)-hypo group), nine without TSBAb (TSBAb(-)-hypo group), and 91 who achieved remission after ATD treatment (Remission group). In the TSBAb(+)-hypo group, TV significantly decreased from the hyperthyroid to hypothyroid phase (median: 33.3 mL [range: 14.2-52.0] vs. 13.6 mL [4.3-23.3], respectively; p = 0.001). In the TSBAb(-)-hypo group, TV significantly decreased from the hyperthyroid to hypothyroid phase (26.6 mL [11.9-49.2] vs. 20.9 mL [7.4-34.2], respectively; p = 0.037). In the Remission group, TV also decreased significantly from the hyperthyroid to remission phase (29.8 mL [8.2-88.4] vs. 25.1 mL [9.5-72.0], respectively; p = 0.0002). The decrease in TV was significantly higher in the TSBAb(+)-hypo group than in the TSBAb(-)-hypo and Remission groups (53.9% [37.9-74.5] vs. 30.9% [-22.3 to 63.0] and 10.7% [-100.7 to 52.0], respectively; p = 0.027 and <0.0001). This study documents the first precise measurement of TV reduction using ultrasonography in patients with GD who developed hypothyroidism with TSBAb, showing a markedly greater decrease than in those without TSBAb or in remission after ATD treatment.