SCINTIGRAPHIC FINDINGS OF THE THYROID IN HYPOTHYROID PATIENTS WITH BLOCKING-TYPE TSH-RECEPTOR ANTIBODIES

The present study was designed to analyse the scintigraphic appearance of the thyroid in hypothyroid patients with blocking-type TSH recepto r antibodies (TRAbs). Eleven hypothyroid patients with autoimmune thyr oiditis positive for TSH binding inhibitor immunoglobulins (TBII) [80% +/- 12 (SD)%; normal <11%] and for thyroid stimulation-blocking antib odies (TSBAbs) (90% +/- 9%; normal <32%) were studied. Thyroid scannin g was performed using technetium-99m or iodine-123, when the patients were hypothyroid. Analysis of the scan images revealed the presence of localized functioning areas in six patients (group 1), and no visuali zation of the thyroid in the remaining five patients (group 2). Patien ts in group 1 showed significantly higher uptake of Tc-99m than those in group 2 (P<0.05). Interestingly, three patients in group 1 were pos itive for thyroid-stimulating antibodies (TSAbs) (249% +/- 17%; normal <145%), which were not detected in the remaining eight patients. Anti bodies against thyroglobulin and microsomal antigens were detected in nine nine (81.8%) and 11 (100%) patients, respectively, but neither of these titres correlated with the scan image. Three patients in group 1 underwent scintigraphy again after treatment with thyroxine, at whic h time the functioning lesion was not noted. Fourteen hypothyroid pati ents with negative TBII displayed no such scintigraphic findings. Chro nic stimulation of the thyroid by TSAbs and/or TSH might be responsibl e for the presence of the functioning lesion, but clarification of the mechanism requires further studies. In summary (1) TSAbs were detecte d in three (27.3%) of 11 hypothyroid patients with blocking TRAbs; (2) thyroid scintigraphy revealed the presence of localized functioning a rea(s) in approximately half of these cases.