Clinical characteristics of Graves' orbitopathy in patients showing discrepancy between levels from TBII assays and TSI bioassay

Objective To investigate clinical characteristics of patients with Graves' orbitopathy (GO) who showed discrepancies between levels of thyroid-stimulating immunoglobulin (TSI) and thyrotropin-binding inhibitory immunoglobulin (TBII). Design Comparative case series. Patients A total of 317 patients with GO in whom Mc4-TSI and M22-TRAb (third-generation TBII) were measured simultaneously. Patients were divided into four groups according to TRAb levels as followings: Group 1, TBII and TSI < median value; Group 2, TBII ≥ median, TSI < median; Group 3, TBII < median, TSI ≥ median; Group 4, both TBII and TSI ≥ median. Measurement Endocrine and ophthalmic clinical manifestations in each group. Results The median value of M22-TRAb was 6·11 IU/l and that of Mc4-TSI was 415·1 (SRR%). One hundred seventeen patients were classified as Group 1, 41 patients as Group 2, 41 patients as group 3 and 118 patients as group 4. Mean CAS was significantly higher in Groups 3 (2·2) and 4 (2·2) than in Groups 1 (1·6) and 2 (1·4; P = 0·001, anova). Mean modified NOSPECS scores were significantly higher (P < 0·001, anova) in Groups 3 (4·1) and 4 (4·1) than in Groups 1 (3·1) and 2 (2·3). The proportion of patients with hyperthyroidism was larger in Group 2 (85·4% [35/41 patients]) than in Group 3 (48·8% [20/41 patients]; P = 0·002). Conclusions GO is more active and severe in patients with predominant Mc4-TSI than in patients with predominant M22-TRAb. Patients with hyperthyroidism were more likely to be included with patients with predominant M22-TRAb than with predominant Mc4-TSI.