Myeloperoxidase Antineutrophil Cytoplasmic Antibody-Associated Renal-Limited Vasculitis in a Young Adult Woman.

Antineutrophil cytoplasmic antibody (ANCA)-associated renal-limited vasculitis (RLV) is a minor subtype of small vessel vasculitis characterized by the inflammation of blood vessels, tissue damage, and loss of renal function localized in the kidney without systemic involvements. Here, we report a case of myeloperoxidase (MPO) ANCA-associated RLV in a young adult woman in Japan presenting chronic hematuria and newly overt proteinuria. Percutaneous renal biopsy revealed focal fibro-cellular crescent glomerulonephritis and the absence of other small vasculitides, tubular atrophy, and interstitial fibrosis. Therapeutic intravenous methylprednisolone pulse followed by oral prednisolone was administered as a remission induction. The patient's serum MPO-ANCA level gradually decreased, coinciding with dramatic changes in proteinuria and hematuria after therapeutic glucocorticoid administration. Renal function was maintained within the normal range, and disease activity was well-tolerated throughout the follow-up period for more than 14 weeks. While the incidence of RLV is rare among younger patients, it occurs with asymptomatic hematuria and proteinuria, which is important in differentiating RLV from typical glomerulonephritis. The overall prognosis of ANCA-associated RLV potentially depends on the severity of extrarenal involvements. Early diagnosis, appropriate treatment, and regular maintenance are essential for controlling and treating RLV. Due to the nontypical case presented here, further investigation is recommended to improve the diagnosis strategies and treatment options for this disease.