Thymic Origin of Abnormal Lymphoid Cells in Sézary Syndrome

A patient with a 5-year history of pruritus and progressive and generalized erythroderma was found to have abnormal lymphocytes in the peripheral blood and mononuclear dermal infiltrate, all of which are features consistent with those described in Sézary syndrome. Systemic chemotherapy produced an almost complete resolution of skin lesions and pruritus. Serial studies on the abnormal cells included responses to phytohemagglutinin, cytogenetics, and immunofluorescence tests for identification of B or T lymphocytes. The abnormal cells demonstrated hyperdiploidy; the ratio of B to T cells fell whenever abnormal lymphocytes appeared in the peripheral blood, and returned to normal when abnormal cells disappeared from circulation. Lymphocytes separated from a skin nodule labeled as T cells. We conclude that the abnormal lymphocytes in this patient are of thymic origin.