A child of microscopic polyarteritis nodosa effectively treated with intravenous methylprednisolone pulses and serial cyclophosphamide pulse therapy

: Microscopic polyarteritis nodosa (mPAN) is a rare disorder in pediatric field of systemic small vessel vasculitis, and affects skin and musculoskeletal system accompanied by progressive necrotizing glomerulonephritis. We described here a 15-year-old boy with positive anti-neutrophil cytoplasmic antibody (MPO-ANCA) and severe mPAN, who was effectively treated with intravenous methylprednisolone pulse therapy followed by monthly cyclophosphamide pulses for 1 year. The histologic examination of renal biopsy specimen showed a severely desolated disease characterized by fibrinoid necrosis, crescent formation of most glomeruli and interstitial infiltration of inflammatory cells. The elevated titers of MPO-ANCA were useful markers for diagnosis, and the serial determinations of the antibody titers were indicative of disease activity. Moreover, dramatic clinical improvement after the induction of the combinatorial therapy and the disappearance of MPO-ANCA was correlated in the disease course. In this report, the serial determination of MPO-ANCA constituted a useful diagnostic tool and a sensitive marker of disease activity.