Myositis in a patient with large granular leukocyte leukemia

We describe the case of a 58-year-old patient with subacute progressive weakness in both legs accompanied by recurrent opportunistic infections. White cell count was normal, but immunophenotyping revealed an increased number of CD8⁺ T cells and deficiency of natural killer cells, B cells, and CD4⁺ T cells in the peripheral blood. Large granular leukocyte (LGL) leukemia was diagnosed based on a clonal T-cell receptor rearrangement. Muscle biopsy demonstrated severe myositis with extensive CD8⁺ T-cell infiltrates. Since no evidence of microbial muscle infection was found, autoimmune myositis was diagnosed. Immunosuppressive treatment resulted in clinical improvement and normalization of creatine kinase (CK) serum levels. The immunological phenotype of the patient and the positive response to treatment adds further to the concept that CD8⁺ T cells mediate disease in autoimmune myositis.