Prognosis of microscopic polyangiitis is well predictable in the first 2 weeks of treatment

Background Kidney and life outcomes remain unsatisfactory in patients with microscopic polyangiitis (MPA).

Appropriate treatment intensity must be provided to the appropriate patients.

To identify severe cases early, we investigated the factors related to kidney and life outcomes.

Methods We included patients diagnosed with MPA based on myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA) positivity and kidney histopathology results after kidney biopsies between January 1, 2021, and May 11, 2023, at 10 affiliated centers, including our hospital.

Death, maintenance dialysis, and estimated glomerular filtration rate (eGFR) < 15 after 6 months of treatment were defined as poor prognosis groups, and factors associated with these conditions were investigated.

Results We included 84 (36 men and 48 women) patients in this study.

Median age was 73.8 (interquartile range: 71–81) years.

After 6 months of treatment, the proportion of patients in the poor prognosis group was 16.7 %, with a mortality of 7.1 % and a poor kidney prognosis rate of 9.5 %.

Area under the receiver operating characteristic curve showed that eGFR at 2 weeks had a comparable prognostic performance equal as eGFR at 4 weeks (area under the curve: 0.875 and 0.896, respectively).

After adjustment by various factors, eGFR at 2 weeks was related with prognosis significantly (p = 0.031).

Conclusion Kidney function 2 weeks after the start of treatment for MPA can predict prognosis.