Markers of pulmonary injury and inflammation are elevated in the serum of patients with chronic cough

Introduction: Cough is a debilitating symptom with a significant impact on quality of life. Patients with refractory chronic cough typically cough hundreds of times per day therefore we hypothesised that the associated pressures and shearing forces may lead to micro-injury of the pulmonary tissues. Aims: To compare lung and tissue injury biomarkers in the blood of refractory chronic cough patients (RCC) with healthy volunteers (HV). Methods: Serum from 64 RCC (75% female; mean age 54.3yrs) and 34 HV (62% female; mean age 36.7yrs) was assayed. Surfactant Protein-D (SP-D) and matrix metalloproteinase (MMP)-7 were measured using a commercial ELISA kit; C Reactive protein (CRP), Intercellular Adhesion Molecule (ICAM)-1, Serum amyloid A (SAA), Vascular cell adhesion protein (VCAM)-1 were measured using V-PLEX Vascular Injury Panel 2. Two tailed Mann-Whitney-U tests were performed. Results: All markers of micro-injury were significantly elevated in RCC patients compared with HV, with the most striking elevations seen in SP-D (302 vs 187 ng/mL, p<0.0005), SAA (1595 vs 519ng/mL; P<0.0001) and CRP (2546 vs 926 ng/mL; P<0.0005), see figure 1. Conclusion: Markers of epithelial damage (SP-D and MMP-7), vascular injury (VCAM-1 and ICAM-1) and peripheral tissue injury (CRP and SAA) were all elevated in the serum of chronic cough patients, supporting the hypothesis that cough is associated with lung micro-injury.