Polyarthritis and neutropenia associated with circulating large granular lymphocytes

Five patients with polyarthritis and neutropenia had numerous circulating large granular lymphocytes with a phenotype attributed to immature natural killer cells. All five had splenomegaly and recurrent infections. Arthritis was most prominent at the wrists and hands, and all patients were considered to have atypical cases of Felty's syndrome. Antinuclear antibodies, rheumatoid factor, antineutrophil antibodies, and immune complexes were detected in most patients. Bone marrow biopsies revealed a maturation arrest at the myelocyte stage and lymphoid infiltrates. Large lymphocytes with azurophilic cytoplasmic granules were found on peripheral blood smears and showed a characteristic reactivity pattern with monoclonal antibodies suggesting a natural killer cell lineage. Peripheral blood mononuclear cells showed less than normal natural killer activity against K562 target cells. Increased numbers of large granular lymphocytes with a phenotype of immature natural killer cells may be important in the pathogenesis of neutropenia, humoral immune disturbances, and synovitis in a subset of patients with Felty's syndrome.