Anti-neutrophil cytoplasmic antibodies associated interstitial pneumonia: A possible new clinical entity

Anti-neutrophil cytoplasmic antibodies (ANCA), a hallmark of systemic vasculitis (SV), have been reported in patients with idiopathic interstitial pneumonia (IIP). However, the clinical significance of ANCA in IIP remains unclear.

We retrospectively studied 101 IP patients diagnosed by pneumologists as idiopathic interstitial pneumonia (IIP,64) and IP with autoimmune features (IPAF,37). ANCA, anti-myeloperoxidase and anti-proteinase-3 were tested by immunofluorescence and ELISA. Chest HRCT patterns, pulmonary function tests (PFTs) and the evolution to SV during a 12-month follow-up were assessed. Multivariable regression analysis was performed to assess the association of baseline covariates with SV. The proximity of patients with close characteristics was investigated by cluster analysis.

Twenty-one patients (20.8%) were ANCA+, similarly distributed between IPAF and IIP. ANCA+ patients were more likely to have NSIP (p = .02) and bronchiectasis (p = .02) on HRCT, less impaired 6MWD (p = .02), higher CRP (p = .02) and more arthralgias (p < .001) than ANCA- patients. During follow-up, 9 (43%) p-ANCA+ patients, but no ANCA- patients, developed SV (p = .001). p-ANCA+ IP had 26.3 OR (95% CI 3.20-36.8) to evolve to SV within 12 months (p < .0001). Cluster analysis identified one group of 25 patients with significantly higher baseline NSIP (88%), p-ANCA+ (48%), arthralgias (32%), and SV (24%) at 12 months. Nevertheless, 12 p-ANCA+ IP patients never developed SV.

ANCA+ IP patients had a high risk of developing SV and need close monitoring and prompt immunotherapy. ANCA+ IP patients not evolving to SV had a diagnosis of IIP or IPAF. These patients need longer observational studies to investigate if they represent a distinct ILD entity.