[1517] Atypical Lymphoplasmacytic Proliferation in the Thyroid: Critical Appraisal of the Conventional Morphologic Criteria for Extranodal Marginal Zone Lymphoma

Payal Sojitra, Girish Venkataraman, Scott S Smith, Milind M Velankar. Loyola University Medical Center, Maywood, IL

Background: Distinction between primary extranodal MALT lymphoma of thyroid and lymphocytic thyroiditis is not easy. We describe four atypical thyroidal lymphoplamacytic proliferations spanning the spectrum of benign through lymphoma highlighting the diagnostic pitfalls and need for judicious use of ancillary studies to make this distinction.
Design: These 4 cases were seen at our institution between 2010 - 2012. Case 4 had history of follicular lymphoma (FL; lambda restricted) on rituximab. Histology and immunohistochemical stains were reviewed in all while additional PCR for IgH@ rearrangements were examined in 2 of 4 cases.

Pathology summary of 4 cases
Case IDLymphocytic thyroiditisIF B-cell InfiltratePlasmacytosis/clonalityDestructive B-LEL
IF, interfollicular; PC, polyclonal

Results: The age range was 44-83 yr including three females. Main features of all cases are depicted in table 1. Case 1 highlights that T-lymphoepithelial lesions (LELs) may be misconstrued leading to the erroneous diagnosis of lymphoma. Case 2 showed low-grade B-cell lymphoma with extensive plasmacytic differentiation, several reactive follicles and destructive B-LELs. Although light chain restricted (LCR) plasmacytic differentiation was demonstrable by light chain stains, a whole section PCR was negative and only macrodissection with enrichment led to the identification of clonality by PCR. Case 3 highlights the need for careful assessment for focal involvement by MALT lymphoma which may not show immunophenotypic evidence of LCR; a diagnosis of lymphoma is possible based on extensive 'stuffed' destructive B-LELs with a post-germinal center MUM-1+ phenotype. Case 4 was notable for prior FL and showed kappa LCR-plasmacytic proliferation without evidence of a concurrent B-cell component, likely owing to rituximab therapy. Although this is clonally unrelated to the prior FL, an exact subclassification (MALT with extensive plasmacytic differentiation vs. plasmacytoma) could not made.
Conclusions: Spectrum of lymphoplasmacytic proliferations in thyroid is wider that what is known so far in literature. Careful attention to multiple features (and not any one single feature) like presence of interfollicular B- cell infiltrate, destructive B-cell LELs, monoclonal plasma cells and clonal B-cell gene re-arrangement study help distinguish MALT lymphoma of thyroid from lymphocytic thyroiditis.
Category: Hematopathology

Tuesday, March 5, 2013 1:00 PM

Poster Session IV # 258, Tuesday Afternoon


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