Correlation between cough frequency and airway inflammation in children with primary ciliary dyskinesia

Cough is common in airway disease. We measured cough frequency in children with primary ciliary dyskinesia (PCD), to determine how accurately families assess this symptom; and to assess the relationship between cough frequency and airway inflammation, measured using induced sputum and exhaled nitric oxide (eNO). Twenty stable PCD children (7 boys), median age 10.8 years (interquartile range (IQR), 9-14), and 10 healthy control children, median age 12 years (IQR, 10.5-12.7), were recruited. ENO was measured using a chemiluminescence analyzer, with sputum induction with 3.5% saline. PCD children underwent ambulatory cough monitoring. Sputum neutrophils were higher in PCD (median, 70.3%; IQR, 55.3-78%) compared to controls (median, 27%; IQR, 24.5-33%; P = 0.004); cough frequency was higher (median episodes, 19; IQR, 11-22.5) compared to healthy children (median episodes, 6.7; IQR, 4.1-10.5; P < 0.001). Forced expiratory volume in 1 sec (FEV(1) percent predicted) and eNO were lower in PCD (median, 63%; IQR, 57-85%; P < 0.0001); eNO (median, 7.1 ppb (IQR, 4.8-19.1 ppb) vs. 12.4 ppb (IQR, 10.3-17.3 ppb), P = 0.043). Parental scoring of day and night cough correlated with recorded cough (r = 0.930, P < 0.0001, daytime; r = 0.711 for nighttime, P = 0.002). Visual analogue score and cough episodes also correlated positively (r = 0.906; P < 0.0001). There was a positive correlation between cough frequency and sputum neutrophil count in PCD (Spearman's r = 0.693, P < 0.002), but not percent FEV(1) or eNO. Stable PCD children have increased cough frequency and neutrophilic airway inflammation. In conclusion, cough frequency correlated with sputum neutrophils but not with FEV1 or eNO.