Incidence, prevalence, mortality and chronic renal damage of anti-neutrophil cytoplasmic antibody-associated glomerulonephritis in a 20-year population-based cohort

Abstract

Background: True population-based clinical and outcomes data are lacking for anti-neutrophil cytoplasmic autoantibody (ANCA)-associated glomerulonephritis (AAGN). Therefore we aimed to estimate the incidence, prevalence and mortality of AAGN, as well as the relationship between the grade of chronic renal damage at presentation and renal and non-renal outcomes.

Methods: Patients with AAGN were identified among a population-based incident cohort of 57 Olmsted County residents diagnosed with ANCA-associated vasculitis (AAV) in 1996-2015. Incidence rates were age and sex adjusted to the 2010 US white population. Age- and sex-adjusted prevalence was calculated for 1 January 2015. Survival rates were compared with expected rates in the Minnesota population. Chronic renal damage was assessed by chronicity score (CS) on biopsies performed at diagnosis.

Results: Thirty-four (60%) patients had AAGN. Of these, 65% had microscopic polyangiitis (MPA) and 74% were myeloperoxidase (MPO)-ANCA positive. The annual incidence of AAGN was 2.0/100 000 population [95% confidence interval (CI) 1.3-2.7] and the overall prevalence was 35/100 000 (95% CI 24-47). Mortality for AAGN was increased (P < 0.001), whereas mortality for AAV without glomerulonephritis did not differ from the general population. Minimal to mild CS predicted recovery of renal function at 1 year; clinical diagnosis (granulomatosis with polyangiitis versus MPA) and ANCA specificity (proteinase 3 versus MPO) did not. This observation was replicated in an independent cohort of 38 newly diagnosed AAGN patients seen at our centre over the 1999-2014 period.

Conclusions: The annual incidence and prevalence of AAGN in Minnesota are 2.0/100 000 and 35/100 000, respectively. Mortality is worse compared with AAV patients without glomerulonephritis. More advanced renal damage at diagnosis predicts less renal recovery.

Keywords: ANCA-associated vasculitis; glomerulonephritis; granulomatosis with polyangiitis; nephritis; renal insufficiency.

FIGURE 1

Patient survival in AAV without AAGN (n = 23; solid line) compared with patients with AAGN (n = 34; dashed line) at AAV incidence and expected age-, sex-, and calendar year–adjusted mortality in Minnesota for those without AAGN (dotted line) and for those with AAGN (dashed/dotted line).

FIGURE 2

Light microscopy showing grades of chronicity in renal biopsies. Each panel is one patient biopsy. (A and B) Mild chronic changes, (C and D) moderate chronic changes and (E and F) severe chronic changes. Minimal chronic changes were not represented since changes are absent or hardly perceptible. All stains are Masson trichrome, except B, which is a periodic acid–Schiff stain. Thin arrows point to areas of tubular atrophy and interstitial fibrosis (A, C, E). Thick arrows point to glomerular lesions: small cellular crescent (B), large area of segmental fibrinoid necrosis (necrotizing lesion) (D) and segmental sclerosis/scar (F).

FIGURE 3

(A) Chronic renal damage at diagnosis, as assessed by CS in renal biopsies, was significantly associated with renal recovery at 6 months and 12 months (based on eGFR) (A), whereas (B) ANCA serology (PR3-AAV versus MPO-AAV) and (C) clinical diagnosis (GPA versus MPA) were not.

FIGURE 4

Age- and sex-adjusted patient survival by CS class: minimal/mild (n = 14; dashed line) versus moderate/severe (n = 8; solid line) [HR 2.30 (95% CI 0.45–11.70); P = 0.31 adjusted for age and sex].