Chronic unexplained cough triggered by environmental irritants is characterized by increased cough reflex sensitivity, which can be demonstrated by means of inhaled capsaicin. Topical capsaicin can be used to improve non-allergic rhinitis and intestinal hypersensitivity and to reduce neuropathic pain.
Objectives: We established whether an oral intake of natural capsaicin (chilli) could desensitize the cough reflex and improve unexplained coughing.
Methods: Twenty-four patients with irritant-induced, unexplained chronic cough and 15 controls were included in the study. For 4 weeks, the participants took capsules with pure capsaicin, and for 4 weeks, they took placebo capsules. The protocol was crossover, randomized, and double blind. Cough sensitivity during the study was evaluated by a standardized capsaicin inhalation cough test that assessed the capsaicin concentration required to reach two coughs (C2) and five coughs (C5). Participants were also administered questionnaires on cough and cough-related symptoms.
Results: Three patients withdrew before the study end, one during the active treatment period and two during the placebo period. After treatment with capsaicin, the thresholds for C2 were higher (improved) both in patients (p < 0.020) and in controls (p < 0.0061) compared to after the placebo period. Among patients, the concentration needed to reach C2 (p < 0.0004) and C5 (p < 0.0009) increased after the period with the active substance compared to cough thresholds at baseline. The cough symptom scores improved after 4 weeks of active treatment (p < 0.0030) compared to the baseline scores.
Conclusion: Capsaicin powder taken orally decreased capsaicin cough sensitivity and cough symptoms. The findings suggest a desensitization of the cough-sensitive transient receptor potential vanilloid-1 (TRPV1).
Keywords: Capsaicin; Chronic cough; Desensitization; Sensory hyperreactivity.
Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.