IgG4-positive extranodal marginal zone lymphoma arising in Hashimoto's thyroiditis: clinicopathological and cytogenetic features of a hitherto undescribed condition.
OBJECTIVE
Hashimoto's thyroiditis was recently divided into IgG4-plasma cell-rich and IgG4-plasma cell-poor subtypes. The former, also known as IgG4 thyroiditis, is associated with clinical, serological, sonographic and morphological features that are distinctive from those of the non-IgG4 subgroup. We describe an interesting case of IgG4-positive mucosa-associated lymphoid tissue (MALT) lymphoma arising in a background of IgG4 thyroiditis.


RESULTS
The thyroid gland showed typical features of IgG4 thyroiditis, including characteristic patterns of fibrosis. A dense lymphoplasmacytic infiltrate diffusely involved the entire gland without formation of a destructive tumour mass. Lymphoepithelial lesions were prominent. There were abundant IgG4-positive plasma cells, with the IgG4/IgG ratio exceeding 40%. The IgG4-positive plasma cells were monotypic for kappa light chain, and there was monoclonal IGH rearrangement. Fluorescence in-situ hybridization revealed IGH translocation without translocation of MALT1, bcl-10, or FOXP1.


CONCLUSIONS
This represents the first case of IgG4-producing MALT lymphoma associated with IgG4 thyroiditis. IGH translocation with an unknown partner gene was identified. We suggest the performance of serum and immunohistochemical investigations for IgG and IgG4 in all cases of Hashimoto's thyroiditis to diagnose IgG4 thyroiditis. In addition, clonality assays and light chain studies are useful to exclude a low-grade lymphoma arising in this context.
Department of Pathology, National University Health System, Singapore.
Char-Loo
CL
Tan
Department of Otolaryngology-Head & Neck Surgery, National University Health System, Singapore.
Yew-Kwang
YK
Ong
Department of Pathology, Singapore General Hospital, Singapore.
Soo-Yong
SY
Tan
Department of Pathology, National University of Singapore, Singapore.
Siok-Bian
SB
Ng
D044963:Biopsy, Fine-Needle; D020732:Cytogenetic Analysis; D050031:Hashimoto Disease / Q000150:complications* / Q000235:genetics / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D018442:Lymphoma, B-Cell, Marginal Zone / Q000150:complications* / Q000235:genetics / Q000276:immunology / Q000473:pathology; D008297:Male; D008875:Middle Aged; D014178:Translocation, Genetic
D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains
Hashimoto's thyroiditis; IgG4; MALT; lymphoma; translocation