Double-positive CD4(+)CD8(+) Sézary syndrome: an unusual phenotype with an aggressive clinical course.

Sézary syndrome (SS) is a rare, aggressive form of cutaneous T-cell lymphoma. When patients die from SS, it frequently is due to the sequela of the profound endogenous immunosuppression that is typical of this condition. Most cases of SS represent neoplasms of mature postthymic CD4(+) T cells. We present a case of SS that exhibited an unusual double-positive phenotype in which the neoplastic T cells demonstrated CD4 and CD8 expression. The patient's clinical course was unusually aggressive with rapid clinical demise occurring less than 1 year from the initial cutaneous eruption. Our patient had documented involvement of the skin, peripheral blood, and lymph nodes. We also review other anecdotal reports of postthymic T-cell lymphomas manifesting as a double-positive phenotype primarily in the context of adult T-cell leukemia and T-cell lymphoma. The evolution of the postthymic double-positive T-cell phenotype, especially with regard to SS, and the benign lymphocyte counterpart also is discussed.