The aetiology of chronic cough: a review of current theories for the otorhinolaryngologist

Irritant-Induced Chronic Cough Triggers: A Scoping Review and Clinical Checklist

Purpose The primary aim of this review was to identify environmental irritants known to trigger chronic cough through the life span and develop a comprehensive clinically useful irritant checklist. Method A scoping review was conducted using the Preferred Reporting Items for Systematic Review and Meta-Analysis Extension for Scoping Reviews, checklist, and explanation. English-language, full-text resources were identified through Medline, PsycINFO, SPORTDiscus, Web of Science, and ProQuest Dissertations and Theses Global. Results A total of 1,072 sources were retrieved; of these, 109 were duplicates. Titles of abstracts of 963 articles were screened, with 295 selected for full-text review. Using the exclusion and inclusion criteria listed, 236 articles were considered eligible and 214 different triggers were identified. Triggers were identified from North America, Europe, Africa, Asia, and Australia. Occupational exposures were also delineated. Conclusions A clinically useful checklist of both frequently encountered triggers and idiosyncratic or rare triggers was developed. The clinical checklist provides a unique contribution to streamline and standardize clinical assessment of irritant-induced chronic cough. The international scope of this review extends the usefulness of the clinical checklist to clinicians on most continents.

Fewer acute respiratory infection episodes among patients receiving treatment for gastroesophageal reflux disease

Patients with gastroesophageal reflux disease (GERD) present with comorbid complications with implications for healthcare utilization. To date, little is known about the effects of GERD treatment with a proton-pump inhibitor (PPI) on patients’ subsequent healthcare utilization for acute respiratory infections (ARIs). This population-based study compared ARI episodes captured through outpatient visits, one year before and one year after GERD patients received PPI treatment. We used retrospective data from the Longitudinal Health Insurance Database 2005 in Taiwan, comparing 21,486 patients diagnosed with GERD from 2010 to 2012 with 21,486 age-sex matched comparison patients without GERD. Annual ARI episodes represented by ambulatory care visits for ARI (visits during a 7-day period bundled into one episode), were compared between the patient groups during the 1-year period before and after the index date (date of GERD diagnosis for study patients, first ambulatory visit in the same year for their matched comparison counterpart). Multiple regression analysis using a difference-in-difference approach was performed to estimate the adjusted association between GERD treatment and the subsequent annual ARI rate. We found that the mean annual ARI episode rate among GERD patients reduced by 11.4%, from 4.39 before PPI treatment, to 3.89 following treatment (mean change = -0.5 visit, 95% confidence interval (CI) = (-0.64, -0.36)). In Poisson regression analysis, GERD treatment showed an independent association with the annual ARI rate, showing a negative estimate (with p<0.001). The study suggests that GERD treatment with PPIs may help reduce healthcare visits for ARIs, highlighting the importance of treatment-seeking by GERD patients and compliance with treatment.

Expert opinion on the cough hypersensitivity syndrome in respiratory medicine

In 2011, a European Respiratory Society Task Force embarked on a process to determine the position and clinical relevance of the cough hypersensitivity syndrome, a disorder characterised by troublesome coughing often triggered by low levels of thermal, mechanical or chemical exposure, in the management of patients with chronic cough. A 21-component questionnaire was developed by an iterative process supported by a literature review. 44 key opinion leaders in respiratory medicine were selected and interviewed as to their opinions. There was a high degree of unanimity in the responses obtained, with all opinion leaders supporting the concept of cough hypersensitivity as a clinically useful paradigm. The classic stratification of cough into asthmatic, rhinitic and reflux-related phenotypes was supported. Significant disparity of opinion was seen in the response to two questions concerning the therapy of chronic cough. First, the role of acid suppression in reflux cough was questioned. Secondly, the opinion leaders were split as to whether a trial of oral steroids was indicated to establish a diagnosis of eosinophilic cough. The cough hypersensitivity syndrome was clearly endorsed by the opinion leaders as a valid and useful concept. They considered that support of patients with chronic cough was inadequate and the Task Force recommends that further work is urgently required in this neglected area.

Classification of chronic cough by systematic treatment cascade trial starting with beta agonist

Background

Chronic cough is one of the most challenging symptoms to diagnose and treat, not only because of the variety of underlying disorders but also its varying susceptibility to treatments. Etiological studies of chronic cough vary depending on the clinical settings and the particular interests of investigators.

Objectives

The purposes of this study were first to categorize the etiology of chronic cough by its response to systematic diagnostic treatments starting from the β₂ agonist and second to sub-categorize β₂ agonist responsive cough (BRC) by the airway hyperresponsiveness.

Methods

One hundred and eighty-four never-smokers received the maximal dose of procaterol to diagnose BRC. BRC was sub-categorized into two groups with or without airway hyperresponsiveness measured by the methacholine challenge test. Sinobronchial syndrome (SBS) was diagnosed by postnasal drip symptoms and by the response to clarythromycin and carbocysteine. Atopic cough (AC) was diagnosed by the evidence of atopy and the response to cetirizine hydrochloride. Gastroesophageal reflux disease (GERD) was diagnosed by the response to rabeprazole sodium. Since we did not investigate eosinophil counts in the tissue or in the induced sputum, no diagnosis of eosinophilic bronchitis was made.

Results

One hundred and nine patients had BRC. Twenty-three of them had bronchial asthma (BA), 53 had cough variant asthma (CVA) and 33 had non-hyperresponsive BRC (NHBRC). Thirty-one patients had GERD, 27 had AC and 14 had SBS. Twenty-five patients had more than one diagnosis in combination, while 6 had other miscellaneous diseases. Twelve patients were undiagnosed and 11 dropped out of the study.

Conclusions

The majority of chronic cough was BRC. NHBRC was a new chronic cough entity. GERD is a common cause of chronic cough in Japan, as in Western countries. AC and SBS are also causes of chronic cough in Japan.

Trial registration

University hospital medical information network (UMIN 000007483)

Chronic cough and OSA: a new association?

Chronic cough is defined as cough lasting more than 2 months. Common causes for chronic cough in nonsmokers with normal chest radiographs and pulmonary functions include gastroesophageal reflux disease (GERD), cough-variant asthma (CVA), and upper airway cough syndrome (UACS). Current guidelines recommend diagnosing the etiology of chronic cough based upon the results of therapy for suspected GERD, CVA, and UACS. Despite following current recommendations for diagnosis and treatment, the cause for a significant proportion of chronic cough remains unexplained.Recent reports indicate the resolution of chronic cough following treatment of concomitantly diagnosed obstructive sleep apnea (OSA). Whether this represents a co-occurrence of two commonly prevalent disorders or a pathophysiologic relationship between OSA and cough remains unknown. This review offers insights into a pathophysiologic link between OSA and the commonly purported etiologies for cough, namely, GERD, UACS, and CVA. In addition, evidence for a relationship between airway inflammation that can trigger or perpetuate cough and OSA is discussed. This review explores mechanisms by which nocturnal continuous positive airway therapy resolves cough by improving underlying airway inflammation secondary to OSA and impacts upon GERD, CVA, and UACS.

Chronic cough: a multidisciplinary approach

BACKGROUND AND METHODS

Chronic cough is defined as a cough persisting for more than eight weeks. This condition generates significant healthcare and economic costs. It is associated with a spectrum of disorders across multiple medical specialties and can provide significant challenges for effective evaluation and management. The current literature was reviewed to gain further insight into chronic cough, including its relationship with sinonasal disease.

RESULTS

Within the reviewed literature, there was strong emphasis on post-nasal drip syndrome as a major causative factor.

CONCLUSION

Cough is the most common complaint for which adult patients seek medical consultation in primary care settings. Chronic cough is associated with a deterioration in the quality of patients' lives. Thorough assessment of a patient with a chronic cough relies on a multidisciplinary approach.

Factors affecting outcome of inferior turbinate mucotomy in treatment of postnasal drip syndrome

BACKGROUND

Postnasal drip syndrome may result from isolated hyperplasia of nasal inferior turbinates due to chronic rhinitis. Mucotomy (conchotomy) performed in such patients is generally effective but in some individuals the problem persists after surgery.

OBJECTIVE

The aim of this study was to determine factors influencing outcome of the therapy.

METHODS

One hundred six patients aged 17-60 years (mean = 34, SD = 12) with hyperplasia of the inferior turbinates underwent bipolar diathermy mucotomy. Nonallergic noninfectious rhinitis was diagnosed in 18, neutrophilic in 58, allergic in 18 and NARES in 14 patients. The participants were questioned about postnasal drip (PND) intensity before and 2 months after surgery.

RESULTS

Results of mucotomy significantly depended on the etiology of chronic rhinitis and were worst in patients with NARES (p < 0.05). Percent values of reduction of PND intensity after mucotomy and percent of daytime with PND persisting after surgery depended on Staphylococcus aureus colonization of the nose (the results were worse in patients with the colonization, p < 0.001). Satisfaction scores were also dependent on S. aureus nasal colonization (p < 0.001) and significantly correlated with percent values of subjective reduction of PND intensity after surgery (p < 0.001) and reduction of PND daily duration (p < 0.001).

CONCLUSIONS

Results of mucotomy performed for postnasal drip depend on etiology of rhinitis and are worse in S. aureus nasal colonization.

Factors associated with computed tomography status in patients presenting with a history of chronic rhinosinusitis

BACKGROUND

The diagnosis of chronic rhinosinusitis (CRS) is based upon symptomatic criteria and objective measures. However, patients suspected to have CRS based on a positive history but negative endoscopies remain a diagnostic challenge. We investigated the utility of point of care computed tomography (POC-CT) in resolving this issue.

METHODS

The study group consisted of a simple random sample of 100 patients presenting with active CRS symptoms and negative endoscopies who underwent POC-CT at initial presentation. Presenting symptoms and comorbidities were correlated with CT scan results (positive/negative) using univariate and multivariate logistic regression models.

RESULTS

POC-CT was considered positive in 49% of patients. Univariate analysis revealed that patients complaining nasal obstruction were significantly more likely to have a positive scan (odds ratio [OR], 2.74; p = 0.047), while those with postnasal drip (OR, 0.44; p = 0.047) or cough (OR, 0.17; p = 0.03) were less likely to have positive scan results. In the multivariate model, these trends persisted without reaching statistical significance. Under univariate analysis, patients who were prescribed antibiotics, oral steroids, or nasal steroids at this initial visit were more likely to have had a positive CT. These trends also persisted in the multivariate model, with significance observed for the association between antibiotic prescription and a positive scan (p = 0.001).

CONCLUSION

Less than 50% of patients with active CRS symptoms had radiographic manifestations of sinus disease. Other etiologies must be considered higher in the differential for those presenting primarily with complaints referable to the throat. POC-CT averted unnecessary antibiotics in these patients.

Future directions in treating cough

Cough is a common and troublesome symptom that can be difficult to treat. New therapeutic options that are safe and more effective than those currently available are needed. In this article, the authors offer opinion on future directions in the treatment of cough, with a particular emphasis on the clinical syndrome associated with cough reflex hypersensitivity. In addition, the article provides an overview of some of the diagnostic technologies and promising drug targets likely to emerge from current clinical and scientific endeavor.

Chronic cough in upper airway diseases

BACKGROUND

The epidemiological, pathophysiological and clinical links between upper and lower airways are nowadays clearly demonstrated. Most of asthmatics are suffering from rhinitis while up to 40% of rhinitic patients have asthma. Asthmatics and COPD patients are also prone to develop concomitant chronic rhinosinusitis (CRS). This study aimed to determine the predictive value of cough for concomitant asthma in patients suffering from upper airway diseases.

METHODS

This cross-sectional study described a group of 143 consecutive patients suffering simultaneously from common upper and lower airway disorders. Both ENT-specialists and respiratory physicians consecutively examined the patients in Ghent University Hospital from October 2004 till October 2006. This study was based on the demographic characteristics, upper and lower airway conditions.

RESULTS

Forty-seven percent of the patients included in the study were males and the mean age of studied population was 43.6 years. The major complaint was chronic cough. When present, patients with chronic cough have an increased risk of suffering from a concomitant asthma in both allergic rhinitis (OR=5.8) and CRS with nasal polyps (OR=10.4), but not in CRS without polyps.

CONCLUSIONS

Chronic cough was found to be a key symptom of associated asthma in allergic rhinitis and CRS with nasal polyps. Interestingly, chronic cough in CRS without nasal polyps did not show the same predictive value: this suggests different pathophysiological mechanisms.

Postnasal drip and chronic cough: An open interventional study

BACKGROUND

The postnasal drip (PND) syndrome is often linked as a cause of chronic cough although this is disputed.

OBJECTIVES

We examined the effect of specific topical treatment of rhinosinusitis on cough in patients presenting with a chronic cough associated with a postnasal drip or 'nasal catarrh'.

METHODS

Patients presenting with a chronic cough and who complained of PND were enrolled and symptoms of PND and cough were assessed by questionnaire and by a capsaicin cough response. Rhinosinusitis was assessed by questionnaires, direct examination of the nose and by high-resolution computed tomography. In an open study, they were treated with fluticasone nasules, ipratropium bromide and azelastine nasal sprays for 28 days, after which they were re-assessed.

RESULTS

Eighteen out of 21 patients completed the study. All patients reported having the presence of mucus in the throat. Mean cough score improved post-treatment (p<0.05), but there was no significant change in capsaicin cough sensitivity or nasal catarrh questionnaire score. There was improvement in anterior nasal discharge symptom scores (p=0.005) and in endoscopic nasal scores post-treatment (p<0.01), with a tendency to improved PND scores.

CONCLUSION

In a pilot open 'real-life' study treatment targeted towards rhinosinusitis accompanying PND syndrome and chronic cough led to an improvement in cough. A randomised controlled study is now needed to confirm or refute these findings.

Clinical cough VI: the need for new therapies for cough: disease-specific and symptom-related antitussives

Cough is a common symptom that can be self-limiting or persistent. Ideally, treatment of the underlying cause(s) of cough with specific treatments should eliminate cough. This approach may not be successful if no cause can be established or if the treatment of the cause fails. Suppression of cough may be disease-specific or symptom-related. There has been a long tradition in acute cough usually due to upper respiratory tract infections to use symptom-related antitussives. In chronic cough, suppression of cough may be achieved by disease-specific therapies, but in many patients it may be necessary to use symptomatic antitussives. The efficacy of some over-the-counter symptomatic antitussives is often no better than that of a placebo. Currently available cough suppressants include the centrally acting opioids such as morphine, codeine, pholcodeine, and dextromethorphan. Early studies reported success in reducing cough in patients with chronic bronchitis or chronic obstructive pulmonary disease (COPD); however, a carefully conducted blinded controlled study showed no effect of codeine on cough of COPD. Success with these cough suppressants may be achieved at high doses that are associated with side effects. A slow-release preparation of morphine has been shown to have some degree of efficacy, but this should be reserved for the most severe chronic cough patient, and for patients with terminal cancer who may also benefit from its analgesic effects. There are case reports of the success of centrally acting drugs such as amitriptyline, paroxetine, gabapentin, and carbamezepine in chronic cough. New agents derived from basic research such as new opioids such as nociceptin or antagonists of transient receptor potential vanniloid-1 may turn out to have antitussive effects. Efficacy of symptomatic cough suppressants must be tested in double-blind randomized trials using validated measures of cough in patients with chronic cough not responding to specific treatments. Patients with chronic cough need effective antitussives that could be used either on demand or on a long-term basis.

Clinical cough II: therapeutic treatments and management of chronic cough

Chronic cough is a common and frequently disruptive symptom which can be difficult to treat with currently available medicines. Asthma/eosinophilic airway disease and gastro-oesophageal reflux disease are most commonly associated with chronic cough but it may also trouble patients with chronic obstructive pulmonary disease, pulmonary fibrosis and lung cancer. Over the last three decades there have been a number of key advances in the clinical approach to cough and a number of international guidelines on the management of cough have been developed. Despite the undoubted benefit of such initiatives, more effective treatments for cough are urgently needed. The precise pathophysiological mechanisms of chronic cough are unknown but central to the process is sensitization (upregulation) of the cough reflex. One well-recognized clinical consequence of this hypersensitive state is bouts of coughing triggered by apparently trivial provocation such as scents and odours and changes in air temperature. The main objective of new treatments for cough would be to identify ways to downregulate this heightened cough reflex but yet preserve its crucial role in protecting the airway. The combined efforts of clinicians, scientists and the pharmaceutical industry offer most hope for such a treatment breakthrough. The aim of this chapter is to provide some rationale for the current treatment recommendations and to offer some reflections on the management of patients with chronic cough.

Prevalence, pathogenesis, and causes of chronic cough

Cough is a reflex action of the respiratory tract that is used to clear the upper airways. Chronic cough lasting for more than 8 weeks is common in the community. The causes include cigarette smoking, exposure to cigarette smoke, and exposure to environmental pollution, especially particulates. Diseases causing chronic cough include asthma, eosinophilic bronchitis, gastro-oesophageal reflux disease, postnasal drip syndrome or rhinosinusitis, chronic obstructive pulmonary disease, pulmonary fibrosis, and bronchiectasis. Doctors should always work towards a clear diagnosis, considering common and rare illnesses. In some patients, no cause is identified, leading to the diagnosis of idiopathic cough. Chronic cough is often associated with an increased response to tussive agents such as capsaicin. Plastic changes in intrinsic and synaptic excitability in the brainstem, spine, or airway nerves can enhance the cough reflex, and can persist in the absence of the initiating cough event. Structural and inflammatory airway mucosal changes in non-asthmatic chronic cough could represent the cause or the traumatic response to repetitive coughing. Effective control of cough requires not only controlling the disease causing the cough but also desensitisation of cough pathways.

Common causes and current guidelines

Chronic cough is a common and disabling symptom. Recent guidelines have attempted to provide direction in the clinical management of cough in both primary and secondary care. They have also provided a critical review of the available literature and identified gaps in current knowledge. Despite this they have been criticized for a reliance on a low quality evidence base. In this review, we summarize the current consensus on the clinical management of chronic cough and attempt to rationalize this based on recent evidence. We have also provided an overview of the likely pathophysiological mechanisms responsible for cough and highlighted areas, where knowledge deficits exist and suggest directions for future research. Such progress will be critical in the search for new and effective treatments for cough.

Currently Available Cough Suppressants for Chronic Cough

Chronic cough is a common symptom but only a fraction of patients seek medical attention. Addressing the causes of chronic cough may lead to control of cough; however, this approach is not always successful since there is a certain degree of failure even when the cause(s) of cough are adequately treated; in idiopathic cough, there is no cause to treat. Persistent cough may be associated with deterioration of quality of life, and treatment with cough suppressants is indicated. Currently available cough suppressants include the centrally acting opioids such as morphine, codeine, and dextromethorphan. Peripherally acting antitussives include moguisteine and levodropropizine. Early studies report success in reducing cough in patients with chronic bronchitis or COPD; however, a carefully conducted study showed no effect of codeine on cough of COPD. Success with these cough suppressants can be achieved at high doses that are associated with side effects. Slow-release morphine has been reported to be useful in controlling intractable cough with good tolerance to constipation and drowsiness. There have been case reports of the success of centrally acting drugs such as amitryptiline, paroxetine, gabapentin, and carbamezepine in chronic cough. New opioids such as nociceptin or antagonists of TRPV1 may turn out to be more effective. Efficacy of cough suppressants must be tested in double-blind randomised trials using validated measures of cough in patients with chronic cough not responding to specific treatments. Patients with chronic cough are in desperate need of effective antitussives that can be used either on demand or on a long-term basis.

Effective antitussives for the cough patient: an unmet need

Chronic cough is a prevalent symptom in the community but it is likely that only a small fraction of chronic coughers seek medical attention. Chronic cough can be controlled by addressing the 'cause' of the cough, but not all cough is controlled using this approach; an 'idiopathic' cough or cough of unknown aetiology is becoming more well-recognized. In these patients and in those whose cough has not responded to treatment of the cause(s), there is a lack of efficacious antitussive therapies ('non-specific' antitussives). Even in those whose cough is controlled by treatment of the cause, an efficacious antitussive for symptomatic relief would be useful for breakthrough symptoms. It is necessary to address the mechanisms underlying chronic cough, particularly the process of sensitization, both peripherally and centrally, that is the basis of chronic cough; such a process may persist even in the absence of the initiating event that first induced the cough. Currently-available antitussives in both acute and chronic cough are not very effective. Novel targets that may result in effective antitussives have been identified and with the development of clinical tools to measure cough accurately and reliably (e.g. cough counts and cough-specific quality-of-life questionnaires) and the evoked cough response (e.g. citric acid or capsaicin challenges), clinical trials should be performed. The chronic cough population is clinically heterogeneous but is characterized by an enhanced cough reflex; this should be the target population for study. Patients with chronic cough are in desperate need of effective antitussives that can be used either on demand or on a long-term basis.