Slowly progressive ANCA-associated renal vasculitis. Clinico-pathological characterisation and outcome

Background. Although rapidly progressive glomerulonephritis is the main renal phenotype of anti-neutrophil cytoplasmicantibody (ANCA)-associated vasculitis (AAV), slow renal disease progression is sometimes observed. These forms have beenrarely discussed; we analysed their prevalence, clinico-pathological characteristics and outcome. Methods. We screened patients with microscopic polyangiitis (MPA) and granulomatosis with polyangiitis followed at seven referral centres and selected those with estimated glomerular filtration rate (eGFR) reduction<50% over a 6-month period preceding diagnosis. Data regarding patient features and response to treatment were retrieved. Results. Of 856 patients, 41 (5%) had slowly progressive renal AAV. All had MPA and all but one was P-ANCA/myeloperoxidase (MPO) ANCA-positive. At diagnosis, the median age was 70 years [interquartile range (IQR) 64–78] and extra-renal manifestations were absent or subclinical (interstitial lung lesions in 10, 24%). The median (IQR) eGFR was23 mL/min/1.73 m2(15–35); six patients (15%) had started renal replacement therapy (RRT). All had proteinuria (median1180 mg/24 h, IQR 670–2600) and micro-haematuria. Main histologic findings were extracapillary proliferation at chronicstages and glomerulosclerosis; following Berden’s classification, 6/28 biopsies (21%) were ‘focal’, 1/28 (4%) ‘crescentic’, 9/28(32%) ‘mixed’ and 12/28 (43%) ‘sclerotic’. At last follow-up (median 32 months, IQR 12–52), 20/34 patients (59%) treated with immunosuppression had eGFR improvement>25% as compared with diagnosis, while 4/34 (12%) had started RRT. Conclusions. AAV may present with slow renal disease progression; this subset is hallmarked by advanced age at diagnosis,positive MPO-ANCA, subclinical interstitial lung lesions and chronic damage at kidney biopsy. Partial renal recovery may occur following immunosuppression.