Purpose. Since recent reports suggest that
Hashimoto thyroiditis (HT) may be associated with
IgG4-related disease, we aimed to find out whether the measurement of serum
IgG4 allows for the identification of distinct types of HT, with different clinical, sonographic, and serologic characteristics. Methods. The group studied consisted of 53 patients with HT and 28 healthy individuals who underwent thyroid ultrasonography and body composition analysis. Serum concentrations of
IgG4, TSH, anti-
peroxidase antibodies (TPOAb), anti-
TSH receptor antibodies, TNF-α, TGF-β1,
Fas Ligand, TRAIL, and
chemokines (CXCL9, CXCL11, and CXCL10) were measured by ELISA or radioimmunoassay. Results. The group with
IgG4 level >135 IU/ml accounted for 32.5% of the patients. The signs of
fibrosis were present in 27.0% of the high-IgG4 patients and in 9.1% of the normal-IgG4 group. The patients with elevated
IgG4 required higher doses of
L-thyroxine and had significantly lower level of TPOAb (P=0.02) than the non-IgG4-HT individuals and higher TNF-α level in comparison with the controls (P=0.01). Conclusions. Our results suggest that the measurement of serum
IgG4 allows for an identification of patients with more rapid progression of HT, requiring higher doses of
L-thyroxine. Low TPOAb level and the absence of coexisting
autoimmune diseases may suggest distinct pathomechanism of this type of
thyroiditis.