The Epidemiology of Antineutrophil Cytoplasmic Autoantibody-Associated Vasculitis in Olmsted County, Minnesota: A Twenty-Year US Population-Based Study

Abstract

Objective: To estimate the annual incidence, prevalence, and mortality of antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) and its subsets, granulomatosis with polyangiitis (Wegener's) (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (Churg-Strauss) (EGPA), in a US-based adult population.

Methods: All medical records of patients with a diagnosis of, or suspicion of having, AAV in Olmsted County, Minnesota from January 1, 1996 to December 31, 2015 were reviewed. AAV incidence rates were age- and sex-adjusted to the 2010 US white population. Age- and sex-adjusted prevalence of AAV was calculated on January 1, 2015. Survival rates observed in the study cohort were compared with expected rates in the Minnesota population.

Results: Of the 58 incident cases of AAV in Olmsted County during the study period, 23 (40%) were cases of GPA, 28 (48%) were cases of MPA, and 7 (12%) were cases of EGPA. Overall, 28 (48%) of the patients with AAV were women and 57 (98%) were white. The mean ± SD age at diagnosis was 61.1 ± 16.5 years. Thirty-four patients (61%) had myeloperoxidase (MPO)-ANCAs, and 17 (30%) were positive for proteinase 3 (PR3)-ANCAs; 5 (9%) were ANCA-negative. The annual incidence of AAV was 3.3 per 100,000 population (95% confidence interval [95% CI] 2.4-4.1). The incidence rates of GPA, MPA, and EGPA were 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. The overall prevalence of AAV was 42.1 per 100,000 (95% CI 29.6-54.6). The mortality rate among AAV patients overall, and among patients with EGPA, those with MPA, and those with MPO-ANCAs, was increased in comparison to the Minnesota general population (each P < 0.05), whereas mortality rates among patients with GPA, those with PR3-ANCAs, and ANCA-negative patients did not differ from that in the general population.

Conclusion: The annual incidence of AAV in Olmsted County, Minnesota over the 20 years of the study was 3.3 per 100,000, with a prevalence of 42.1 per 100,000, which is substantially higher than the rates reported in other areas worldwide. The incidence of GPA was similar to that of MPA. Patients with MPA and those with EGPA, but not patients with GPA, experienced higher rates of mortality than that in the Minnesota general population. MPO-ANCAs were a marker of poor survival in this population of patients with AAV.

Figure 1

Algorithm representing the screening process for the identification of the patients with ANCA-associated vasculitis diagnosed in Olmsted County, Minnesota (USA) from 1996 to 2015. Footnotes: *All the patients aged < 18 years were excluded due to residency coincidentally.

Figure 2

Age- and sex-adjusted incidence rates of ANCA-associated vasculitis in adults (age ≥ 18 years) in Olmsted County, Minnesota. (A) Annual incidence of the entire AAV cohort (solid line), GPA (dashed line) and MPA (dotted line). (B) Annual incidence of the entire AAV cohort (solid line), PR3-ANCA patients (dashed line) and MPO-ANCA patients (dotted line). Annual incidence trends of EGPA and ANCA-negative patients were not examined due to small sample size.

Figure 3

Survival rates of Olmsted County residents with ANCA-associated vasculitis compared to expected rates from Minnesota lifetables (observed, solid line; expected dashed line): entire AAV cohort (A), stratified by diagnosis (B, C) or by ANCA status and specificity (D, E). Survival rates of EGPA and ANCA-negative patients were not examined due to small sample size.