SPECIFIC EFFECTS OF RADIOIODINE TREATMENT ON TSAB AND TBAB LEVELS IN PATIENTS WITH GRAVES-DISEASE

Radioactive iodine (RAI)-induced changes in the levels of antibodies t o the thyroid-stimulating hormone (TSH) receptor (TRAb) in patients un dergoing treatment for autoimmune thyroid disease have been well docum ented. Previous studies have reported effects on the overall level of the antibodies present, TSH-binding inhibitory immunoglobulins (TBII), without detailed studies of specific effects on the levels of thyroid -stimulating (TSAb) or thyroid-blocking antibodies (TBAb). More detail ed studies have been reported only in individual cases. In this study, the values of TSAb, TBAb, and TBII were measured longitudinally in 33 patients (27 females and 6 males) who received RAI. The bioassays for TSAb and TBAb were performed in JPO9 cells. Following RAI, there were significant and immediate effects on the values of TBII in 70% of pat ients. TBII levels feb in 7 patients (20%) (Group 1), rose in 16 patie nts (48%) (Group 2) or remained unchanged but elevated in 10 patients (32%) (Group 3). In the Group 1 patients, only TSAb were detectable an d none of these patients became hypothyroid after treatment. In the 16 patients in Group 2, increases in TBII were attributable to specific increases in TSAb in 7 (44%), in TBAb in 3 (19%), and in both TSAb and TBAb in 3 (19%). There were 3 patients (19%) in this group in whom th ere was no detectable TSAb or TBAb activity despite the increase in TB II. Six patients from this group became hypothyroid within 6 months of RAI treatment. In the 10 patients in Group 3, 5 patients (50%) were p ositive for TBAb only, 2 (20%) were TSAb-only positive, and 3 (30%) we re both TSAb- and TBAb-positive. Five patients (50%) in this group bec ame hypothyroid and all had TBAb present in their circulation. Our res ults show that there are diverse changes in TBII, TSAb, and TBAb follo wing RAI. Hypothyroidism occurred in 33% of the patients treated with RAI therapy and TBAb were present in 75% of these hypothyroid patients . When TBAb were present in the absence of TSAb, hypothyroidism occurr ed in 6 of 8 versus 3 of 14 where TSAb were present alone (p < 0.05). The development of hypothyroidism within 6 months of RAI treatment was not related to continuation or dosage of antithyroid drugs and was tr ansient in 50% of patients. We conclude that early hypothyroidism foll owing RAI therapy is associated with increased TBAb in some patients a nd that recognition of this clinical situation should avoid unnecessar y life-long thyroxine replacement.