Myeloperoxidase-Anti-Neutrophil Cytoplasmic Antibody Vasculitis With Isolated Renal Presentation in an Older Female Patient: A Diagnostic and Therapeutic Challenge.

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides are rare systemic autoimmune diseases, the incidence of which increases in older individuals. We report the case of a 76-year-old woman whose routine laboratory workup revealed acute kidney injury with a serum creatinine level of 155 µmol/L and significant proteinuria (2.5 g/24 h). ANCA testing was strongly positive for anti-myeloperoxidase (MPO) antibodies. A renal biopsy confirmed pauci-immune glomerulonephritis with moderate interstitial fibrosis and glomerulosclerosis, consistent with ANCA-associated vasculitis. Induction therapy consisted of corticosteroids and rituximab, which was discontinued following a suspected drug-related cutaneous reaction. Cyclophosphamide was successfully used as an alternative induction treatment. Following negative allergological evaluation and cautious re-exposure, rituximab was subsequently resumed for maintenance therapy and was well tolerated. Late-onset MPO-ANCA-associated vasculitis can have a favorable prognosis when diagnosed early and managed with appropriate immunosuppressive regimens.