The prevalence of bronchitis and associations with spirometry in patients with interstitial lungdisease in a Canadian tertiary care centre

Abstract

Cough in diffuse interstitial lung diseases (ILD) is a common and debilitating symptom with many proposed causative factors. The contribution of airway inflammation to cough has not been quantified and the association between bronchitis and lung function has not been measured. Sputum cell counts (SCC) could potentially be theragnostic for cough in ILD. The objectives of this study are to describe the prevalence of bronchitis, as measured by SCC, in patients with chronic cough and ILD to determine if bronchitis is associated with significant changes in spirometry. This is a retrospective study of patients with ILD who had a SCC ordered for chronic cough at the Firestone Institute from 2005-2018. Patients were identified from a sputum database and ILD clinic lists and the criteria for bronchitis (based on normative values) were applied. SCC was completed 303 times for ILD patients (n=175). The most common diagnostic categories were idiopathic interstitial pneumonia (29.3%) and CTD-ILD (27.6%), with idiopathic pulmonary fibrosis the most common condition (10.2%). SCC demonstrated eosinophilic, neutrophilic, and lymphocytic bronchitis in 31.1%, 29.1%, and 6.4% of cases, respectively. The presence of bronchitis was associated with a lower FEV1 (µ=1.98 vs 2.31L, p=0.003, t-test) and FVC (µ=2.51 vs 2.92L, p=0.003, t-test), but bronchitis was not predictive of FEV1 or FVC in a multivariate model. In a Canadian tertiary care centre, bronchitis was common in patients with ILD and chronic cough. Though bronchitis was associated with lower spirometry, it was not predictive of FEV1 or FVC when incorporated in a multivariate model.