Antineutrophil Cytoplasmic Antibodies Negative Microscopic Polyangiitis With Initial Pulmonary Manifestation

ABSTRACT

Microscopic polyangiitis (MPA) is a small vessel vasculitides mostly associated with anti-neutrophil cytoplasmic antibodies (ANCA). The kidney is the most commonly affected organ in MPA. We report the case of a 9-year-old girl with ANCA-negative MPA who initially presented with respiratory symptoms, including cough, sputum, and dyspnea. Based on her symptoms, atypical pneumonia was suspected. Also, childhood interstitial lung disease was considered based on findings seen on chest CT. Despite initial improvement of symptoms with oral corticosteroid therapy, dyspnea with initiation of corticosteroid tapering was noted. A final diagnosis of MPA was made after lung biopsy. ANCA was negative in both the initial and repeat blood tests. Oral cyclophosphamide and prednisolone treatments led to full remission. Since then, the patient has been treated with low dose prednisolone and azathioprine for maintenance. A good treatment response was achieved and her clinical symptoms, pulmonary functions, and radiologic findings have since improved. Thus, early and precise diagnosis of MPA is crucial for remission induction and prevention of symptom relapse.