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

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.