Cough reflex testing with inhaled capsaicin in the study of chronic cough

Abstract

Objectives: To assess the utility of capsaicin test in the differential diagnosis of non-productive causes of chronic cough and to examine the effects of treatment on this reflex. Participants: 86 healthy volunteers and 101 patients with chronic cough: asthma ( n: 54), gastroesophageal reflux ( n: 35) and post-nasal drip syndrome ( n: 12). Design: Prospective intervention trial. Spirometry, bronchoprovocation test with histamine (PC 20), and cough challenge with ascending concentrations of capsaicin (0.49–500 μM) were initially performed in all subjects. Patients were treated for 3 months according to the origin of the cough. Concentrations that elicited two ( C 2) and five or more coughs ( C 5) were determined before and after treatment. Results: In healthy subjects, cough sensitivity to capsaicin was not influenced by gender or smoking status; however, women with chronic cough were more sensitive to cough challenge than men. C 2 and C 5 were significantly lower in patients with asthma or gastroesophageal reflux than in post-nasal drip syndrome. No significant correlation was observed between the capsaicin cough threshold and PC 20. Cough sensitivity did not improve significantly in most patients with asthma or gastroesophageal reflux despite adequate medical treatment during 3 months. Discriminative value of capsaicin test to differentiate healthy subjects from patients with asthma or reflux was poor. Conclusions: Cough sensitivity to inhaled capsaicin is a safe and reproducible tool in the study of chronic cough. However, its usefulness for the management and differential diagnosis is limited.