Programmatic desensitization of the cough reflex in patients with refractory chronic cough

Dailey, Emma, M.S., Spring 2020 Speech-Language Pathology Programmatic Desensitization of the Cough Reflex in Patients with Refractory Chronic Cough Chairperson: Laurie Slovarp, Ph.D, CCC-SLP Aim: The purpose of this blinded, randomized, placebo-controlled pilot clinical trial was to determine the potential of treating refractory chronic cough (RCC) using a progressive desensitization model paired with behavioral cough suppression. Methods: Twelve adults with chronic cough who had failed behavioral cough treatment enrolled in and completed the study. Participants were randomly assigned to a treatment (n=8) or placebo group (n=4). The study consisted of three phases. During Phase I, participants completed baseline testing, including cough sensitivity testing with capsaicin, the Leicester Cough Questionnaire (LCQ), urge-to-cough-testing, and 24-hour cough frequency testing. During Phase II, participants practiced behavioral cough suppression while receiving a cough stimulant, capsaicin, via nebulizer across six sessions. The treatment group received progressive doses of capsaicin, while the placebo group received one, consistent, low level dose of capsaicin. During Phase III, cough outcomes were repeated at one-week and three-weeks post-treatment. The Mann-Whitney U test was used to determine between-group differences on change scores. The Friedman test followed by pair-wise comparisons with a Bonferroni correction was used to analyze change across time for the entire sample. Results: A Mann Whitney U test demonstrated weak evidence for differences between the treatment group (n=8) and placebo group (n = 4) between baseline and one-week post-treatment for the LCQ (p = 0.23), UTC testing for total coughs (p = 0.107) and mean reported UTC (p = .184) that favored the treatment group. Cough sensitivity results were variable with a significant increase in capsaicin tolerance (i.e., reduction in cough sensitivity) at one-week post that favored the treatment group (p = .016); however at three-weeks post, capsaicin tolerance was higher for the placebo group (mean rank = 8.5) then the treatment group (mean rank = 5.5). A Friedman test on the entire sample revealed strong evidence for improvement at one-week post for the LCQ, (p = .001), UTC testing for total coughs (p = .016) and mean reported UTC (p = .006), but not cough sensitivity (p = .689). There was no evidence of a change between one-week post and three-weeks post (p =.933). Conclusions: This study investigated the use of progression desensitization with capsaicin paired with behavioral cough suppression for individuals with RCC due to hypersensitivity. Both groups experienced improved quality of life, perceived UTC during UTC testing, and cough frequency during UTC testing following treatment. No change in cough sensitivity was demonstrated; however, high response variability suggests questionable reliability of cough sensitivity testing. Though the study was limited by small sample size and unreliable cough sensitivity results, both groups improved significantly suggesting the need for further research. Investigation is needed to examine patient compliance and refine placebo group methodology to determine the treatment factors that impact outcomes. DESENSITIZATION OF THE COUGH REFLEX