Changing Phenotypes and Clinical Outcomes Over Time in Microscopic Polyangiitis

Area of Science:

• Nephrology
• Rheumatology
• Internal Medicine

Background:

• Diagnosis and management of microscopic polyangiitis (MPA) have evolved.
• It remains unclear if clinical presentation, histological findings, and patient/renal outcomes have changed over time.

Purpose of the Study:

• To compare clinical and histopathological characteristics at diagnosis.
• To assess changes in the risk of death, end-stage kidney disease (ESKD), and relapse rate in MPA patients over time.

Main Methods:

• Retrospective analysis of 187 MPA patients diagnosed between 1980-2022, divided into two periods: 1980-2001 and 2002-2022.
• Comparison of clinical and histopathological features, mortality, ESKD risk, and relapse rates using statistical models including Kaplan-Meier, Cox-regression, Aalen-Johansen, and Fine-Gray regression.

Main Results:

• Patients diagnosed between 2002-2022 were older, had better kidney function (higher eGFR), and lower prevalence of severe sclerotic lesions compared to 1980-2001.
• The risk of ESKD significantly decreased in the later period (HR 0.30, P < 0.001), with results sustained after adjustments.
• Relapse risk was numerically higher in the 2002-2022 period (HR 1.64, P = 0.075), while patient survival was comparable between groups.

Conclusions:

• MPA kidney involvement has become less severe over recent decades.
• This has led to a reduced risk of ESKD but an increased relapse rate.
• The risk of death associated with MPA has remained comparable across the studied periods.