CD4^-CD8^- T-cell polymyositis in a patient with chronic active Epstein-Barr virus infection

We describe a 17-year-old woman with chronic active Epstein-Barr virus infection (CAEBV), who developed EBV⁺CD4^-CD8^- T-cell polymyositis. At 14 years of age, CAEBV was diagnosed with fever, cytopenia, liver dysfunction, and hepatosplenomegaly. Despite the transient remission of interferon-α therapy, migratory lesions emerged in back and extremities. MRI indicated polymyositis. Biopsy specimens revealed intramuscular infiltration of CD3⁺, CD4^-, CD8^-, CD56^-, and EBV-encoded RNA 1⁺ cells. Circulating CD4^-CD8^-Vδ2/Vγ9 cells increased. γδT-cells contained 20-200 times higher EBV-DNA (2 x 104 copies/μgDNA) than αβT-cells or NK-cells. The ominous polymyositis might denote the musculotropic invasion of EBV⁺γδT-cell lymphoproliferative disease as a consequence of CAEBV.