Endocrine Abstracts

Objectives: A role of IgG4 in Graves’ disease (GD) has been proposed, although the available data are conflicting. In addition, an association between Graves’ orbitopathy (GO) and IgG4-related disease has been postulated, but no firm demonstration has been obtained. Thus, the aim of the present study was to investigate the role of IgG4 in GD.

Methods: We performed a cross-sectional investigation in 351 consecutive patients (F=284, M=67; age 48.2±15 yr.), of whom 306 had Graves’ disease and 45 had toxic nodular goiter (TNG). All patients came to our observation over 36 consecutive months to undergo radioiodine treatment. IgG4 were measured in all patients. The primary outcome was the level of IgG4 in GD patients compared with TNG. Secondary outcomes were: 1) the prevalence of IgG4 levels above the upper limit of normal range (66 mg/dL); 2) the prevalence of IgG4 levels above the cut-off value considered diagnostic for IgG4-RD (135 mg/dL); and 3) within GD patients, the levels of IgG4 and the prevalence of high IgG4 (≥66 mg/dL or ≥135 mg/dL) in patients with and without GO.

Results: IgG4 concentrations in GD patients (53 mg/dL, IQR: 26-94.7) were significantly greater than those in patients with TNG (56 mg/dL; IQR: 25-59; Mann Whitney U: 5.41; P = 0.02). In addition, the prevalence of patients with IgG4 levels above the upper limit of normal range was greater in GD (112/306, 36.6% vs 8/45, 17.7% in TNG; OR: 2.67, 95%CI from 1.2 to 5.9; P = 0.016). The prevalence of patients with IgG4 levels above the cut-off value diagnostic for IgG4-RD was nearly statistically significantly greater in GD patients (46/306, 15% vs 2/45, 4.4% in TNG; OR: 3.8, 95%CI from 0.89 to 16.2; P = 0.071). Limited to GD patients, IgG4 levels and prevalence of high values (≥66 mg/dL or ≥135 mg/dL) did not differ between patients with GO and those without GO.

Conclusions: IgG4 serum levels are higher in patients with GD compared with nonautoimmune hyperthyroidism, with an apparent greater prevalence of values that can be considered relevant. The possible clinical implications of our findings remain to be investigated.