Microscopic Polyangiitis Following Kawasaki Disease in a Patient With Autoimmune Predisposition.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is rare in children, and its pathogenesis remains incompletely understood. Current evidence suggests that complex interactions between genetic susceptibility and environmental triggers contribute to disease development. We report a case of pediatric-onset microscopic polyangiitis (MPA) preceded by recurrent cutaneous manifestations and occurring in a patient with a history of Kawasaki disease and a strong family history of autoimmune diseases. A 14-year-old boy presented with recurrent painful edematous erythema involving the palms, wrists, and dorsum of the feet. Several months later, he developed fever, arthralgia, oral aphthous ulcers, and weight loss. Urinalysis revealed hematuria and proteinuria, and serum myeloperoxidase (MPO)-ANCA levels were markedly elevated. Renal biopsy demonstrated pauci-immune crescentic glomerulonephritis, leading to the diagnosis of MPA. Remission induction therapy with corticosteroids and cyclophosphamide achieved sustained clinical remission without renal dysfunction. The patient had a history of Kawasaki disease in infancy, more than a decade before the onset of MPA. In addition, his mother had rheumatoid arthritis and myasthenia gravis, and his younger sister had immune thrombocytopenic purpura. This case raises the possibility that prior immune-mediated vascular inflammation, together with autoimmune genetic predisposition, may contribute to the later development of MPO-ANCA-associated vasculitis. Further accumulation of similar cases may help clarify the immunopathogenic relationship between Kawasaki disease and AAV.