Partial nodal involvement by marginal zone lymphoma. Use of IGK gene rearrangement analysis in diagnostic work-up.

Nodal marginal zone lymphoma (NMZL) is an indolent B-cell lymphoma that originates from the marginal zone of B-cell follicles. The tumour is rather uncommon, and shares some morphologic and immunophenotypic similarities with the extranodal form of marginal zone lymphomas. However, diagnosis of NMZL implies the exclusion of lymphoplasmacytic lymphoma, follicular lymphoma, and lymph node involvement by extra nodal or splenic marginal zone B-cell lymphoma In addition, its distinction from reactive conditions, including T-zone hyperplasia, are sometimes problematic based on morphologic grounds. We describe a patient who presented with cervical and inguinal lymphadenopathies and high inflammation indexes. Bone marrow and lymph node biopsies were performed for definitive diagnosis. Bone marrow histological and immunophenotypic examinations were normal and excluded haematological disease. In contrast, lymph node evaluation showed some features compatible with a possible lymphoproliferative disorder, even though no definite diagnosis could be made based on morphologic and immunohistochemical investigation. In particular, the problem of a differential diagnosis between NMZL and a florid hyperplasia of monocytoid B-elements was posed. Thus, in order to assess the nature (neoplastic vs. reactive) of the lesion, molecular analysis of the immunoglobulin genes was performed by PCR. Notably, although no clonal rearrangements were revealed by IGHV@ analysis, further evaluation of the immunoglobulin light chain (IGKV@) confirmed the presence of a clonal B-cell population. Accordingly, a final diagnosis of NMZL was made. In conclusion, this case is a good example of the crucial role of complete molecular analysis in the diagnostic work up of lymphoproliferative disorders.