Hashimoto's thyroiditis with elevated serum IgG4 concentrations is not equivalent to IgG4 Hashimoto's thyroiditis

Abstract

Background

Hashimoto's thyroiditis (HT) with serum IgG4 concentrations greater than 135 mg/dl can be diagnosed as elevated serum IgG4 HT. HT can also be classified into IgG4 HT and non-IgG4 HT based on an immunohistochemistry analysis of IgG4. The aim of our study was to determine the relationship between elevated serum IgG4 HT and IgG4 HT.

Method

93 HT patients with both thyroid tissues and serum samples stored before pathological examination were collected. The serum levels of IgG, IgG4, TgAb IgG, TgAb IgG4, TPOAb IgG, and TPOAb IgG4 were measured by ELISAs. The expression levels of IgG4, IgG and TGF-β1 in thyroid tissues were detected by immunohistochemistry.

Results

HT patients were divided into two groups: elevated serum IgG4 HT (n = 12) and non-elevated serum IgG4 HT (n = 81). Hypothyroidism was found in 5/12 cases (41.7%) in the elevated serum IgG4 HT group and 10/81 cases (12.3%) in the non-elevated serum IgG4 HT group (P = 0.023). Serologically, there were no significant differences in the levels of TgAb IgG, TPOAb IgG, TgAb IgG4, and TPOAb IgG4 between the two groups, and the expression of TGF-β1 in thyroid tissues was not significantly different between the groups. Most importantly, the frequency of patients who satisfied the criteria for IgG4 HT diagnosis was comparable (25% vs. 20.9%, P = 0.756).

Conclusions

The measurement of serum IgG4 allows the identification of HT patients closely associated with hypothyroidism. However, our study demonstrated that elevated serum IgG4 HT is not equivalent to IgG4 HT.

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