Background/Purpose: ANCA-associated vasculitis (AAV) is rare, with a worldwide reported annual incidence ranging from 1.2 to 2.0 cases per 100,000 individuals and a prevalence of 4.6-18.4 cases per 100,000 individuals. To date, precise data on AAV incidence, prevalence, and mortality are lacking in the United States (US). We aimed to estimate the incidence, prevalence and mortality rates of AAV and its subsets, granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA), in a US based adult population.

Methods:

All medical records of patients with a diagnosis or suspicion of AAV in a geographically defined region of the US from January 1, 1996 to December 31, 2015 were reviewed. Incidence and prevalence rates were calculated using population denominators for persons aged≥18 years from the US Census with age- and sex-adjustment to the 2010 US white population. Survival rates were compared with expected rates in the population.

Results:

Of 58 incident cases of AAV, 23 (40%) were GPA, 28 (48%) MPA, and 7 (12%) EGPA. Overall, 28 (48%) were women, 57 (98%) were Caucasian, with a mean (SD) age at diagnosis of 61.1 (16.5) years. ANCA was negative in 5 (9%) patients; 34 (61%) were MPO-ANCA and 17 (30%) were PR3-ANCA positive.

The annual incidence of AAV from 1996 through 2015 was 3.3/100,000 population (95%CI:2.4-4.1). GPA, MPA and EGPA incidence was 1.3 (95%CI:0.8-1.8), 1.6 (95%CI:1.0-2.2), and 0.4 (95%CI:0.1-0.6), respectively. Incidence rates by ANCA type were: 0.9 (95%CI: 0.5-1.4) for PR3-AAV, 2.0 (95%CI: 1.3-2.6) for MPO-AAV, and 0.3 (95%CI: 0.0–0.5) for ANCA-negative AAV.

There were 44 patients with prevalent AAV on January 1, 2015 for an overall prevalence rate of 42.1/100,000 (95%CI: 29.6-54.6). Prevalence by clinical diagnosis and ANCA type was: 21.8 (95%CI: 12.9-30.8) for GPA, 18.4 (95%CI: 10.1–26.7) for MPA, 1.8 (95%CI: 0.0–4.4) for EGPA, 19.0 (95%CI: 10.6 –27.3) for PR3-AAV, 19.2 (95%CI: 10.8–27.7) for MPO-AAV, and 2.8 (95%CI: 0.0–6.1) for ANCA-negative AAV.

Standardized mortality ratios (SMR) for AAV overall, and EGPA, MPA and MPO-AAV were increased (2.04, 16.6, 2.04 and 2.17 respectively, p<0.05); whereas mortality of GPA and PR3-AAV did not differ from general population (SMR 0.93 and 1.09, respectively). No death was recorded in ANCA-negative AAV.

Conclusion: The annual incidence of AAV in the US is 3.3/100,000, with a prevalence of 42/100,000, remarkably higher than previous reports. In contrast with most of the previous European studies, GPA and MPA have similar incidence rates, and MPO-AAV has a higher incidence than PR3-AAV. Mortality of MPA and EGPA, but not GPA is higher than the general population. The presence of MPO-ANCA is a marker of poor survival.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-epidemiology-of-anca-associated-vasculitis-in-the-u-s-a-20-year-population-based-study/