Background/Purpose:

Diagnosis of ANCA-associated vasculitis (AAV) and the classification of granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA) is based on clinical and histologic characteristics. The value of renal and non-renal biopsies for classification of AAV is of great interest for the diagnostic work-up. We aimed to evaluate specific histopathologic features of organ biopsies and their contribution to the diagnosis of vasculitis and to the classification of specific AAV subgroups according to ACR criteria and to the preliminary 2017 DCVAS criteria.

Methods:

Retrospective, single-center cohort study in patients with GPA, EGPA and MPA, who have received at least one organ biopsy. Characteristic histopathologic features were analyzed. Diagnosis of vasculitis and classification to subgroups were analyzed with and without consideration of histologic features.

Results:

306 patients (GPA 154, MPA 58, EGPA 94, mean age at diagnosis 55.2±16.5 years, 48% males) diagnosed between 1990-2017, were included. 451 biopsies (168 renal biopsies, 283 non-renal biopsies) were taken at active stage of AAV at initial diagnosis (n=415) or during disease-flair (n=36). 222 patients (72.5%) were ANCA positive (150 cANCA+, 72 pANCA+). In kidney biopsies, glomerulonephritis was described in 78.6%, unspecific inflammation in 26.8% and normal tissue in 1.2%. In non-renal biopsies, vasculitis, granuloma, tissue eosinophilia, unspecific inflammation or normal tissue were reported in GPA 32.9 / 29.4 / 21.2 / 71.8 / 9.4%, MPA 27.3 / 9.1 / 27.3 / 90.9 / 9.1% and EGPA 20.2 / 10.1 / 67.4 / 73.0 / 20.2%; p<0.0001. According to the ANCA status, the distribution was 31.1 / 25.2 / 28.3 / 68.9 / 10.7% in ANCA+ patients and 20.8 / 11.1 / 62.5 / 79.2 / 19.4% in ANCA– patients (p<0.0001). Biopsy results were decisive for diagnosis of vasculitis in 2% of GPA, none of MPA and 8% of EGPA patients. Fulfillment of 1990 ACR criteria depended on inclusion of histology in 6.6% of GPA and 35.5% of EGPA. For the preliminary 2017 DCVAS criteria, histology was decisive in 2% of GPA, 0% of MPA and 21% of EGPA.

Conclusion:

Histologic proof of vasculitis contributes to diagnosis of AAV. The diagnostic value is most prominent for renal biopsies. While classification to EGPA according ACR criteria depends on histology in almost one third of patients, it is critical for GPA in only a few patients. The relevance of biopsy for the preliminary 2017 DCVAS criteria is clearly diminished, remaining most prominent for EGPA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/value-of-histology-for-diagnosis-and-classification-in-anca-associated-vasculitis/