Qualitative assessment of sensations and triggers in chronic cough

Could cough hypersensitivity symptom profile differentiate phenotypes of chronic cough?

Background

Recently, cough reflex hypersensitivity has been proposed as a common underlying feature of chronic cough in adults. However, symptoms and clinical characteristics of cough hypersensitivity have not been studied amongst phenotypes of chronic cough. This study aimed to compare symptom features, such as cough triggers and associated throat sensations, of cough hypersensitivity in patients with asthmatic chronic cough and those with refractory chronic cough (RCC).

Methods

Patients with chronic cough from the Korean Chronic Cough Registry were prospectively evaluated over 6 months. Physicians determined the aetiological diagnosis based on clinical evaluations and responses to treatment at the 6-month follow-up visit. Symptoms of cough hypersensitivity and cough-specific quality of life were assessed using the Cough Hypersensitivity Questionnaire (CHQ) and the Leicester Cough Questionnaire (LCQ), respectively.

Results

The analysis included 280 patients who completed the follow-up: 79 with asthmatic cough (cough variant asthma or eosinophilic bronchitis) and 201 with RCC. Baseline CHQ scores were similar between the groups (8.3±3.7 in asthmatic cough versus 8.9±3.9 in RCC; p=0.215, adjusted for age, sex and LCQ score). There were no significant between-group differences in the LCQ and cough severity Visual Analog Scale scores. Both groups showed a similar negative correlation with LCQ scores (asthmatic cough: r=-0.427, p<0.001; RCC: r=-0.306, p<0.001).

Conclusions

The symptoms of cough hypersensitivity may not distinguish between asthmatic cough and RCC. This suggests that chronic cough is the primary diagnosis in both phenotypes. It indicates a shared mechanism in their cough pathogenesis, despite having potentially different treatable traits.

Patient-reported assessments of chronic cough in clinical trials: accessory or primary endpoints?

Chronic cough is a complex disorder that affects up to 5-10% of the general population. It can be challenging to manage as there are few effective treatments, although several novel antitussives are in clinical development. The endpoints used to assess their efficacy in clinical trials should be optimal; most large clinical trials currently use objective measures as the primary outcome, especially cough frequency. There are strengths in this approach, although taking the view that other measures of chronic cough are less important, including patient-rated cough severity, psychosocial impact and other associated symptoms. Patient-reported outcome measures (PROMs) explore patients' personal experiences of health and disease, and the effects of particular conditions on their lives. Numerous validated PROMs exist for chronic cough, from simple visual analogue scales, to those that focus on cough hypersensitivity and cough-specific quality of life. Medicine regulators in the European Union (EU) and United States of America (USA) encourage the use of PROMs in clinical trials but have voiced concerns over their content validity, clinically meaningful thresholds for change, and discordance with objective measures. There are recent and ongoing studies to address these limitations. This review discusses currently available PROMs used to assess chronic cough and discusses their potential role as primary outcome measures in clinical trials.

Development and validation of a novel questionnaire to describe and assess sensations and triggers associated with refractory and unexplained chronic cough

INTRODUCTION

Refractory or unexplained chronic cough (RUCC) is a common clinical problem with no effective diagnostic tools. The Sensations and Triggers Provoking Cough questionnaire (TOPIC) was developed to characterise cough in RUCC versus cough in other conditions.

METHODS

Content analysis of participant interviews discussing the sensations and triggers of chronic cough informed TOPIC development. Participants with chronic cough completed the draft-TOPIC (a subset repeating 5-7 days later), St George's Respiratory Questionnaire (SGRQ), Cough Severity Diary (CSD) and Global Rating of Change Scale. The draft-TOPIC item list was reduced in hierarchical and Rasch analysis to refine the questionnaire to the TOPIC.

RESULTS

49 items describing the triggers and sensations of cough were generated from participant interviews (RUCC n=14, chronic obstructive pulmonary disease (COPD) n=11, interstitial lung disease (ILD) n=10, asthma n=11, bronchiectasis n=3, cystic fibrosis n=7). 140 participants (median age 60.0 (19.0-88.0), female 56.4%; RUCC n=39, ILD n=38, asthma n=45, COPD n=6, bronchiectasis n=12) completed draft-TOPIC, where items with poor 'fit' for RUCC were removed to create TOPIC (8 trigger items, 7 sensation items). Median TOPIC score was significantly higher in RUCC (37.0) vs ILD (24.5, p=0.009) and asthma (7.0, p<0.001), but not bronchiectasis (20.0, p=0.318) or COPD (18.5, p=0.238), likely due to small sample sizes. The Rasch model demonstrated excellent fit in RUCC (χ2=22.04, p=0.85; PSI=0.88); as expected. When all participant groups were included, fit was no longer demonstrated (χ2=66.43, p=0.0001, PSI=0.89) due to the increased heterogeneity (CI=0.077). TOPIC correlated positively with SGRQ (r=0.47, p<0.001) and CSD (r=0.63, p<0.001). The test-retest reliability of TOPIC (intraclass correlation coefficient) was excellent (r=0.90, p<0.001).

CONCLUSIONS

High TOPIC scores in the RUCC patients suggest their cough is characterised by specific sensations and triggers. Validation of TOPIC in cough clinics may demonstrate value as an aid to identify features of RUCC versus cough in other conditions.