Induced sputum in systemic sclerosis interstitial lung disease: comparison to healthy controls and bronchoalveolar lavage

Background: Induced sputum (IS) is a noninvasive tool, which can be used to collect cellular and soluble materials from lung airways. Objective: To evaluate if IS may be a useful and safe tool for the detection of airway inflammation in patients with interstitial lung disease (ILD) in systemic sclerosis (SSc). Methods: Sixty-eight patients with SSc and ILD as well as 18 healthy individuals (controls) were selected and submitted to IS examination. In 34 of 68 patients with SSc, bronchoalveolar lavage (BAL) was also performed. Safety of IS was assessed by comparison of forced expiratory volume in the first second (FEV1), FEV1/forced vital capacity ratio and peak expiratory flow before and after the IS procedure. Cell composition in samples collected by BAL and IS was correlated, and IS total and differential cell count in SSc patients and controls were compared. Results: The total number of cells was significantly higher in IS samples of SSc patients compared to those of healthy controls. Mean percentage of neutrophils was also higher in SSc patients (41.79 ± 23.89 vs. 27.37 ± 17.90), as well as lymphocytes (17.42 ± 19.70 vs. 3.13 ± 2.28) and eosinophils (2.35 ± 4.43 vs. 0.41 ± 0.46). On the other hand, mean percentage of macrophages was higher in healthy individuals (69.10 ± 19.15 vs. 36.96 ± 20.68). In fluid recovered by BAL, the most frequent cells were macrophages (67.89% ± 17.26), while neutrophils (14.77 ± 17.18%) and lymphocytes (15.62 ± 13.46%) were less frequent and eosinophils (1.66 ± 2.08%) were rare. A similar pattern of cell composition was found in IS samples (41.15 ± 21.67% of macrophages, 39.72 ± 23.15% of neutrophils, 15.28 ± 19.46% of lymphocytes and 2.56 ± 5.03% of eosinophils). Strength of correlation between BAL and IS was significant for macrophages and neutrophils. After IS procedure was performed, improvement of FEV1 (mean value before IS was 85.09 ± 14.44 and 88.93 ± 16.40 after IS) and FEV1/forced vital capacity (mean value before IS was 98.53 ± 12.11 and 105.22 ± 10.78 after IS) was observed. Conclusion: The IS method may allow a noninvasive assessment of cell composition in airway fluid and may contribute to the better understanding of upper/medium airway inflammation in SSc. Future studies are needed to verify whether IS can replace invasive procedures for the detection and monitoring of lung inflammation in SSc.