Fibrous Variant of Hashimoto Thyroiditis, Riedel Thyroiditis and IgG4-related Thyroid Disease: Different Aspects of the Same Pathology. An Interesting Case Report

  • Background / Purpose
    Riedel thyroiditis (RT) and fibrous variant of Hashimoto thyroiditis (FVHT) are rare morphologically similar fibrotic entities and may be part of the spectrum of IgG4-related diseases. RT is characterized by extensive fibrosis and inflammatory infiltrate, also involving the thyroid surrounding tissues, phlebitis, prevalence of IgA and Lambda-Chains1,2. FVHT is an uncommon form of Hashimoto thyroiditis (HT) characterized by marked fibrosis replacing thyroid gland, lymphoid follicles, prevalence of IgG and Kappa-Chains, absence of phlebitis and typical changes of HT in spared gland1,2. In contrast to FVHT, immunoreactivity for Smooth Muscle Actin (SMA) was described in RT3. Here we present a case of overlap between FVHT and RT.

    A 52 year-old Kyrgyzstan woman presented with a rapid thyroid growth. Total thyroidectomy was performed.

    The thyroid was uniformly enlarged (g 134), presenting at histology with marked fibrosis and diffuse lymphoplasmacellular infiltrate, involving surrounding tissues and part of the upper right parathyroid; lymphoid follicles and oncocytic metaplasia were observed. Plasmacells were IgG-positive, with 10% IgG4-positive, and almost equal immunoreactivity for Kappa- and Lambda-Chains. No phlebitis or immunostaining for SMA were seen.

    Discussion & Conclusion
    Our case shows features of both FVHT and RT, but with low levels of IgG4. According to IgG4-cutoff (30-40%)1,4 defined for other organs, this case cannot  be considered IgG4-related. Since a specific IgG4-cutoff for the thyroid has not been established yet, in our opinion, this case represents an overlap between FVHT and RT with 10% of IgG4. Further studies are needed to better define the IgG4-cutoff in IgG4-related thyroid disease.


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