Clinical characteristics and outcomes in microscopic polyangiitis patients with renal involvement: a study of 124 Chinese patients

BACKGROUND: Microscopic polyangiitis (MPA) is a systemic autoimmune disease, and renal involvement is frequently present in MPA. MPA patients with renal involvement may have a worse prognosis. In this study, we aimed to evaluate the prognostic factors associated with all-cause death and renal survival in MPA patients with renal involvement. METHODS: A retrospective observational cohort study was performed. One hundred twenty-four patients newly diagnosed with MPA with renal involvement excluding end-stage renal disease (ESRD) who were hospitalized at the First Affiliated Hospital of Chongqing Medical University from January 2012 to July 2017 were included. All the survivors were followed up with until July 2018. The clinical and laboratory data at the time of the initial MPA diagnosis were collected, and the predictive values of the variables for mortality and renal outcome were analysed. RESULTS: Among the 124 patients, 52 were men (41.9%) and 72 were women (58.1%), and the age range was from 25 to 85 years (63.9±10.6 years). Seventy-six patients (61.3%) had pulmonary involvement. Multivariate Cox analysis revealed that age≥65 years (HR: 2.437; P=0.021), serum creatinine≥500 μmol/L (HR=2.207; P=0.009) and interstitial lung disease (ILD) (HR=2.366; P=0.013) were associated with mortality. Cox multivariate analysis identified that serum creatinine≥500 μmol/L (HR=8.236; P<0.001) and ILD (HR=2.649; P=0.001) were independent detrimental factors for renal survival, and immunosuppressive treatment was a protective factor for renal survival (HR=0.349; P=0.001). The area under the ROC curve (AUC) of the serum creatinine level at diagnosis was 0.705 for mortality and 0.870 for progression to ESRD or the doubling of serum creatinine. CONCLUSIONS: Age, serum creatinine level at diagnosis and ILD were independent predictors of mortality in MPA patients with renal involvement. Serum creatinine level at diagnosis, ILD and immunosuppressive treatment were independently related to renal survival.