Prediction model for respiratory-related mortality in microscopic polyangiitis with interstitial lung disease: multicentre REVEAL cohort study

Objective This study aimed to establish prediction models for respiratory-related mortality in microscopic polyangiitis (MPA) complicated by interstitial lung disease (ILD) using clinical characteristics.Methods We enrolled patients with MPA with ILD between May 2005 and June 2021 in a multicentre cohort of Japanese patients with MPA (REVEAL cohort). We evaluated the demographic, clinical, laboratory, radiological findings, treatments and the presence of honeycombing 1 cm above the diaphragm using chest high-resolution CT (HRCT) on admission. We explored the risk factors predictive of respiratory-related mortality.Results Of 115 patients, 26 cases died of respiratory-related diseases during a median follow-up of 3.8 years. Eighteen patients (69%) died due to respiratory infection, three (12%) had diffuse alveolar haemorrhage, and five (19%) had exacerbation of ILD. In univariate analysis, older age, lower percent forced vital capacity (%FVC), lower percent diffusing capacity of carbon monoxide (%DLCO), and the presence of honeycombing in the right lower lobe were identified as risk factors. Additionally, in multivariate analysis adjusted for age and treatment, %FVC, %DLCO and the presence of honeycombing in the right lower lobe were independently associated with respiratory-related mortality. We created prediction models based on the values of %FVC, %DLCO and presence of honeycombing on chest HRCT (termed "MPF model"). The 5-year respiratory-related death-free rate was significantly different between patients with MPA with ILD stratified by the number of risk factors based on the MPF model.Conclusions Our study indicates that the MPF model may help predict respiratory-related death in patients with MPA with ILD.