Background/Purpose: Microscopic polyangiitis (MPA) is often associated with lung involvement, including alveolar hemorrhage and interstitial pneumonitis (IP). Clinical characteristics of IP in MPA have not been well described. The aim of this study was to determine the prevalence and clinical course of IP in MPA.

Methods: We retrospectively identified MPA patients at a tertiary medical center in Japan between 2002-2014. MPA patients with positive perinuclear anti-neutrophil cytoplasmic antibody (p-ANCA) who presented with renal involvement, including glomerulonephritis, acute and chronic renal failure, or lung disease such as alveolar hemorrhage or IP were selected. Data were collected on clinical features, medications, radiographic imaging (chest X-ray and computed tomography), and clinical outcome

Results: We identified 39 Japanese patients with MPA (Table). Median age was 69 (16-87); 51% were female; median observation period was 33 months (range 3-158). Among 27/39 (69%) who had IP, IP preceded diagnosis of MPA in 9 (33%), was seen upon diagnosis in 15 (56%), and occurred after diagnosis in 3 (11%). IP was not diagnosed in 33% of patients with MPA, over a median observation period of 74 months (range 45-138). Thirty-seven (95%) patients were treated with steroids or immunosuppressants. Acute exacerbation of IP was seen in 4 (15 %), and no radiographic change in 9 (33%) or minimal worsening of IP without clinical significance in14 (52%) on was found. All-cause mortality or death due to pulmonary complication in MPA did not differ between subjects with or without IP.

Conclusion: IP often precedes other manifestations of MPA. Clinical characteristics and outcomes are similar to those without IP. 

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/significance-of-interstitial-pneumonitis-in-microscopic-polyangiitis/