Abstract: 【Abstract】 Objective To investigate the value of flow cytometric analysis of peripheral blood in the diagnosis of erythroderma. Methods A total of 29 patients with erythroderma were collected from Hospital of Dermatology, Chinese Academy of Medical Sciences from September 2017 to December 2020, including 6 with erythrodermic mycosis fungoides （EMF）, 5 with Sézary syndrome （SS）, 18 with inflammatory erythroderma （IE） with different etiologies. Four healthy volunteers served as healthy controls. Flow cytometry was performed to detect peripheral blood lymphocyte subsets, immunophenotypes and clonality, and their differences were analyzed between inflammatory erythroderma and lymphoma-related erythroderma. One-way analysis of variance and least significant difference-t test were used for comparisons between groups. Results The proportions of T cells, B cells, NK cells and CD4-CD8- cells significantly differed among the EMF group, SS group, IE group and control group （all P < 0.001）. The proportion of T cells was significantly higher in the SS group （93.8% ± 3.4%） than in the EMF group （42.7% ± 6.4%） and IE group （46.0% ± 6.8%, t = 12.8, 14.4, respectively, both P < 0.001）, and the proportion of CD4-CD8- cells was significantly lower in the IE group （0.37% ± 0.40%） than in the EMF group （2.93% ± 0.84%） and SS group （2.38% ± 0.74%, t = 9.2, 6.7, respectively, both P < 0.05）. The expression of clonal T-cell receptor β-chain variable region （TCR-vβ） was not detected in healthy controls or IE patients; the T cell subsets expressing clonal TCR-vβ were detected in 3 cases of EMF and all cases of SS, and they were all identified to be cells with a CD4+CD7-CD26- phenotype. There were significant differences among the above 4 groups of subjects in the proportions of CD4+ T lymphocytes expressing chemokine receptors CCR4, CXCR3, CCR5, cutaneous lymphocyte antigen （CLA） or programmed death receptor-1 （PD-1） on the cell surface （all P < 0.001）. Compared with the SS group and EMF group, the IE group showed significant decreased proportions of CD4+ T lymphocytes expressing CCR4, CLA or PD-1 （all P < 0.001）, but significantly increased proportions of CD4+ T lymphocytes expressing CXCR3 or CCR5 （all P < 0.001）. Conclusion Flow cytometric analysis of peripheral blood lymphocyte subsets, immunophenotypes and clonality can provide a reference for the etiological diagnosis of erythroderma, and is helpful for the differential diagnosis between lymphoma-associated erythroderma and inflammatory erythroderma.

Key words: Lymphoma, T-cell, cutaneous, Sézary syndrome, Flow cytometry, Erythrodermic mycosis fungoides, Inflammatory erythroderma, T-lymphocytes, Epitopes, T-lymphocyte, T-cell receptor β-chain variable region