Abstract
BackgroundSolitary plasmacytoma of bone (SPB) is a rare plasma cell neoplasm. It arises in bone as a single locus in the absence of any plasma cell myeloma lesions. Plasma cell neoplasms intrinsically express only one immunoglobulin light chain (IgL)—kappa or lambda—and using this fact, kappa/lambda deviation is the decisive factor for diagnosis. Co-expression of both IgLs in a single tumor cell is extremely rare.Case presentationWe report a case of SPB that arose in the vertebra of a 52-year-old Japanese woman. Histologically, the resected mass showed diffuse plasma cell proliferation. Dual IgL expression was detected by flow cytometry, immunohistochemistry, and in situ hybridization (ISH) targeting IgL mRNA.ConclusionWe have presented an extremely rare case of SPB showing dual expression of kappa and lambda IgLs. This unusual case of plasma cell neoplasia might represent a possible exceptional example of failure of “IgL isotypic exclusion.”
Highlights
Solitary plasmacytoma of bone (SPB) is a rare plasma cell neoplasm
A single B cell expresses the rearranged immunoglobulin heavy chain (IgH) and the either immunoglobulin light chain (IgL) genes transcribed from only one allele each, with the other 4 alleles remaining in the germline configuration
If IgL kappa rearrangement is nonproductive for both alleles, the IgL kappa locus is inactivated by deletion and IgL lambda rearrangement occurs [13, 14]
Summary
The present case of SPB showing dual IgL expression is the first of its kind to have been reported. IgL rearrangement is under strict genetic control, the mechanism involved is still unclear. The present appears to represent an exceptional event that deviates from the traditional “isotypic exclusion” mechanism
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