Development of lupus nephritis in a patient with human T-cell lymphotropic virus type I-associated myelopathy

A 77-year-old Japanese man with a 14-year history of human T-cell lymphotropic virus type I-associated myelopathy developed pancytopenia, proteinuria, renal dysfunction, and hypocomplementemia. Antinuclear antibody and anti-double-stranded DNA antibody test results were positive, and circulating immune complexes were detected. A renal biopsy showed diffuse and global mesangiocapillary proliferation with extensive subendothelial deposits. Immunofluorescence microscopy showed strong granular staining for immunoglobulins and complements in the mesangium and along capillary walls. Electron microscopy showed numerous mesangial and subendothelial electron-dense deposits. From these findings, systemic lupus erythematosus and diffuse global lupus nephritis were diagnosed. This is a rare case of a patient developing lupus nephritis during the long-term course of human T-cell lymphotropic virus type I-associated myelopathy.