Chronic active Epstein-Barr virus infection: A heterogeneous entity requiring a high index of suspicion for diagnosis.

Chronic active Epstein-Barr virus infection of T- and NK-cell type, systemic form, is a rare entity within the spectrum of EBV-driven T- and NK-cell lymphoproliferative disorders. Established diagnostic criteria and a characteristic clinical course help to differentiate it from other closely related EBV-positive neoplasms and clinical states. We present a patient and review the natural history, pathologic features, pathogenesis, and differential diagnosis of this entity.