Kidneys and lungs are the most common organs involved in microscopic polyangiitis (MPA). A retrospective analysis of pediatric MPA patients with pulmonary lesions over the past 10 years was performed to investigate clinical features of MPA in children with pulmonary lesions. There were 9 patients enrolled in our study, including 2 boys and 7 girls, with a median age of 6.6 years at the time of disease onset and a median disease course of 2 months. All of the patients exhibited tachypnea, and 7 exhibited cough and hemoptysis. The most common presentation on pulmonary imaging was ground glass or patchy shadows, which were observed in 6 cases. Seven patients manifested with hematuria and proteinuria, with renal histopathology of fibrinoid necrosis/exudation of the glomerular capillaries. All of the patients presented with normocytic normochromic anemia. Of the 9 patients, 7 were positive for perinuclear antineutrophil cytoplasmic antibody (p-ANCA) and/or myeloperoxidase (MPO), and 2 were positive for p-ANCA/MPO and cytoplasmic ANCA/proteinase 3. Eight patients had normal complement 3 (C3) levels, and one had an elevated C3 level. Five of the 9 patients were positive for antinuclear antibody ANA, and 4 were positive for double strand DNA (ds-DNA) antibody (3 were positive for both). The 7 patients who exhibited renal involvement received steroid plus cyclophosphamide (CTX) treatment. Of these patients, 4 achieved various degrees of remission, 2 were at the beginning of induction therapy, and one was lost to follow-up. Two patients with isolated pulmonary involvement received steroid plus leflunomide treatment and achieved complete remission. Diffuse alveolar hemorrhage was the most frequent presentation of lung involvement in children with MPA, and tachypnea, cough, hemoptysis and anemia were the common clinical symptoms. The majority of these patients exhibited hematuria, proteinuria and renal insufficiency. The efficacy of steroid plus CTX or leflunomide was evident in these patients.
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