Association of bronchoalveolar lavage cellular analysis and radiological findings in fibrotic interstitial lung diseases

Background and aims Inflammation may play a role in driving interstitial lung diseases (ILD). Radiological ground-glass opacity (GGO) may not reliably distinguish fine intralobular fibrosis from inflammatory processes in fibrotic ILD. We therefore investigated the relationship between GGO, fibrosis and leukocytes in bronchoalveolar lavage (BAL). Methods We recruited patients with fibrotic ILD at a single centre between May 2014 and February 2018. The extent of GGO and fibrosis was evaluated by two radiologists. Linear regression examined the association between leucocyte numbers in BAL obtained from the right middle lobe and GGO/fibrosis extent in whole lung, adjusting for age, sex and smoking. A Z-test was used to compare the association between BAL and GGO/fibrosis. Results 316 patients were included. Adjusting analyses for covariates, only BAL eosinophil and eosinophil-to-macrophage ratio were positively associated with GGO involvement (0.23 (95% CI 0.03 to 0.42) p=0.023 and 11.21 (95% CI 1.33 to 21.08) p=0.026). Lymphocyte percentages (fibrosis −0.17 vs GGO −0.02 p=0.046); neutrophil percentages (fibrosis 0.38 vs GGO 0.06 p=0.002); neutrophil-to-lymphocyte ratio (fibrosis 0.63 vs GGO −0.05 p=0.027); neutrophil-to-macrophage ratio (fibrosis 14.08 vs GGO 2.57 p=0.015) and neutrophilia (fibrosis 6.81 vs GGO −0.31 p=0.002) all demonstrated a significantly stronger association with fibrosis than GGO. Conclusions Lack of relationships between radiological GGO and BAL leucocyte counts in fibrotic lung disease indicates that GGO may not always be inflammatory in nature. Higher levels of neutrophils were associated with more extensive fibrosis.