[Pathological significance of plasma cell infiltration in diagnosing lymph node diseases].

To investigate the value of plasma cells for diagnosing lymph node diseases. Common lymphadenopathy (except plasma cell neoplasms) diagnosed from September 2012 to August 2022 were selected from the pathological records of Changhai Hospital, Shanghai, China. Morphological and immunohistochemical features were analyzed to examine the infiltration pattern, clonality, and IgG and IgG4 expression of plasma cells in these lymphadenopathies, and to summarize the differential diagnoses of plasma cell infiltration in common lymphadenopathies. A total of 236 cases of lymphadenopathies with various degrees of plasma cell infiltration were included in the study. There were 58 cases of Castleman's disease, 55 cases of IgG4-related lymphadenopathy, 14 cases of syphilitic lymphadenitis, 2 cases of rheumatoid lymphadenitis, 18 cases of Rosai-Dorfman disease, 23 cases of Kimura's disease, 13 cases of dermal lymphadenitis and 53 cases of angioimmunoblastic T-cell lymphoma (AITL). The main features of these lymphadenopathies were lymph node enlargement with various degrees of plasm cell infiltration. A panel of immunohistochemical antibodies were used to examine the distribution of plasma cells and the expression of IgG and IgG4. The presence of lymph node architecture could help determine benign and malignant lesions. The preliminary classification of these lymphadenopathies was based on the infiltration features of plasma cells. The evaluation of IgG and IgG4 as a routine means could exclude the lymph nodes involvement of IgG4-related dieases (IgG4-RD), and whether it was accompanied by autoimmune diseases or multiple-organ diseases, which were of critical evidence for the differential diagnosis. For common lesions of lymphadenopathies, such as Castleman's disease, Kimura's disease, Rosai-Dorfman's disease and dermal lymphadenitis, the expression ratio of IgG4/IgG (>40%) as detected using immunhistochemistry and serum IgG4 levels should be considered as a standard for the possibility of IgG4-RD. The differential diagnosis of multicentric Castleman's diseases and IgG4-RD should be also considered. Infiltration of plasma cells and IgG4-positive plasma cells may be detected in some types of lymphadenopathies and lymphomas in clinicopathological daily practice, but not all of them are related to IgG4-RD. It should be emphasized that the characteristics of plasma cell infiltration and the ratio of IgG4/IgG (>40%) should be considered for further differential diagnosis and avoiding misclassification of lymphadenopathies.