Contribution of flow cytometry in the diagnosis of cutaneous lymphoid lesions.

The histologic diagnosis of cutaneous lymphoid lesions remains one of the most challenging areas of dermatopathology and is augmented by incorporation of immunophenotypic and genotypic data. To improve the analysis of surface Ig light chain expression and to increase the yield of immunophenotypic data obtained from skin biopsies, we evaluated the utility of flow cytometry in cutaneous lymphoid infiltrates. Flow cytometric immunophenotypic analyses were performed on skin specimens of 19 patients as a part of diagnostic procedures. We found that skin biopsy specimens, including a routine punch biopsy, yield sufficient material for diagnostic flow cytometry. One reactive lymphoid hyperplasia showed polyclonal B cells and no aberrant T cell populations. Ig light chain restriction was detected by flow cytometry and contributed to the diagnosis in 88% (15 of 17) of cutaneous primary or secondary B cell lymphomas, compared to 37% (three of eight) by immunohistochemistry. Nearly one-third of these cases were histologically suspicious but difficult lesions due to processing artifact, mixed cellular infiltrate, or paucity of abnormal cells. Additional markers (3-23) were analyzed by flow cytometry on 15 specimens, and contributed to subclassification of the lymphomas. Our experience demonstrates that flow cytometry can be successfully applied to routine skin biopsies and contributes to the diagnosis and subclassification of cutaneous lymphoid lesions.