Recommendations for the management of cough in adults

Assessing efficacy of therapy for cough

An antitussive agent should reduce the amount of coughing experienced by the patient sufficiently for the patient to appreciate an improvement in cough severity and regard the improvement as sufficient to outweigh any adverse effects or risks associated with the treatment. In recent years the development of objective cough counting devices and cough-specific quality of life tools have vastly improved our ability to appropriately assess the effectiveness of anti-tussive agents and hopefully will lead to the development of safe and effective treatments in the future. This article summarizes current knowledge of methodologies available for assessing cough therapies, the patient groups to study, and the design of clinical trials.

Quality of life in patients with chronic cough

Chronic cough is a relatively common symptom for which effective, acceptable treatments are lacking. Many patients suffer frequent coughing over several years without resolution and this has significant physical, social and psychological consequences. The recent development of cough-specific quality-of-life tools now allows quantification of the burden of coughing both in patients specifically presenting with chronic cough and also in common respiratory conditions.

Acute cough: a diagnostic and therapeutic challenge

BACKGROUND

Acute cough is one of the most common complaints prompting patient visits to healthcare professionals. Despite the broad repercussions of acute cough on patient quality of life, school and work productivity, and public health resources, research on this condition is minimal, as are the available treatment options. Many patients use over-the-counter medicines, which are often ineffective for symptom relief. Some therapies may achieve antitussive activity, but at the expense of unpleasant or intolerable side effects.

UNMET NEEDS

When considering the treatments currently available for the management of acute cough, the multiple limitations of such treatments are quite apparent. Most of these treatments lack clinically proven efficacy and reliability to support their use. This reinforces the need for the generation of quality scientific data from well-performed clinical trials. Hopefully, the result will be the development of safer, more effective and more reliable therapeutic options in the management of acute cough.

COUGH ASSESSMENT AND MANAGEMENT

Acute cough can be due to a variety of causes, and it is worthwhile to consider these pathogenic factors in some detail. It is also important to be familiar with the effects that acute cough has on patients' quality of life, work productivity, and the healthcare system; proper awareness of these effects may contribute to better understanding of the social impact of cough. In reference to the available treatments for the management of acute cough, adequate knowledge of the type of over-the-counter and prescription products in the market, as well as their mode of action and advantages/disadvantages, may provide expanded pharmacotherapeutic opportunities and facilitate better clinical decisions. However, due to the drawbacks of current treatment options, ideas for future cough management and newer products need to be considered and tested.

CONCLUSION

In view of the socio-economic impact of acute cough and the limitations of available treatments, a renewed interest in the management of acute cough needs to be encouraged. The current strategies for acute cough management need to be reassessed, with a focus on developing new, reliable products and formulations with proven efficacy and safety.

Selective expression of a sodium pump isozyme by cough receptors and evidence for its essential role in regulating cough

We have identified a distinct subtype of airway vagal afferent nerve that plays an essential role in regulating the cough reflex. These afferents are exquisitely sensitive to punctate mechanical stimuli, acid, and decreases in extracellular chloride concentrations, but are insensitive to capsaicin, bradykinin, histamine, adenosine, serotonin, or changes in airway intraluminal pressures. In this study we used intravital imaging, retrograde neuronal tracing, and electrophysiological analyses to characterize the structural basis for their peculiar mechanical sensitivity and to further characterize the regulation of their excitability. In completing these experiments, we uncovered evidence for an essential role of an isozyme of Na(+)-K(+) ATPase in regulating cough. These vagal sensory neurons arise bilaterally from the nodose ganglia and are selectively and brilliantly stained intravitally with the styryl dye FM2-10. Cough receptor terminations are confined and adherent to the extracellular matrix separating the airway epithelium and smooth muscle layers, a site of extensive remodeling in asthma and chronic obstructive pulmonary disease. The cough receptor terminals uniquely express the alpha(3) subunit of Na(+)-K(+) ATPase. Intravital staining of cough receptors by FM2-10, cough receptor excitability in vitro, and coughing in vivo are potently and selectively inhibited by the sodium pump inhibitor ouabain. These data provide the first detailed morphological description of the peripheral terminals of the sensory nerves regulating cough and identify a selective molecular target for their modulation.

The Saudi Initiative for Asthma

The Saudi Initiative for Asthma (SINA) provides up-to-date guidelines for healthcare workers managing patients with asthma. SINA was developed by a panel of Saudi experts with respectable academic backgrounds and long-standing experience in the field. SINA is founded on the latest available evidence, local literature, and knowledge of the current setting in Saudi Arabia. Emphasis is placed on understanding the epidemiology, pathophysiology, medications, and clinical presentation. SINA elaborates on the development of patient-doctor partnership, self-management, and control of precipitating factors. Approaches to asthma treatment in SINA are based on disease control by the utilization of Asthma Control Test for the initiation and adjustment of asthma treatment. This guideline is established for the treatment of asthma in both children and adults, with special attention to children 5 years and younger. It is expected that the implementation of these guidelines for treating asthma will lead to better asthma control and decrease patient utilization of the health care system.

Exhaled nitric oxide measurement is not useful for predicting the response to inhaled corticosteroids in subjects with chronic cough

BACKGROUND

Increased concentrations of exhaled nitric oxide (ENO) are identified predominantly in subjects with chronic cough due to conditions that habitually respond well to therapy with inhaled corticosteroids (ICSs). The aim of this study was to assess the usefulness of ENO in predicting the response to ICS therapy in subjects with chronic cough and to determine the relationship between either methacholine or adenosine 5'-monophosphate (AMP) responsiveness and the response to ICS therapy.

METHODS

A total of 43 patients with chronic cough were studied. During the baseline period, ENO measurement, spirometry, and concentration-response studies with both methacholine and AMP were performed. For the next 4 weeks, the patients were treated with inhaled fluticasone propionate, 100 microg twice daily. At baseline (1 week) and during the 4-week treatment period, patients twice daily completed entries in a diary, in which they recorded daytime and nighttime cough symptom scores.

RESULTS

Nineteen patients (44%) responded well to fluticasone therapy. The receiver operating characteristic curve analysis showed that the accuracy of identifying the response to ICS therapy for ENO at baseline was poor. The sensitivity and specificity of ENO for predicting the response to ICS therapy, using 20 parts per billion as the ENO cutoff point, were 53% and 63%, respectively. Differences in both prevalence and degree of airway responsiveness to either methacholine or AMP between fluticasone-responsive subjects and nonresponsive subjects were also not significant.

CONCLUSIONS

Although a significant proportion of subjects with chronic cough respond well to ICS therapy, these patients cannot be identified by ENO levels or AMP responsiveness at baseline.

Effect of the management of patients with chronic cough by pulmonologists and certified respiratory educators on quality of life: a randomized trial

BACKGROUND

The role of certified respiratory educators (CREs) is to educate, assess, and help to manage patients with asthma and COPD in Canada. This study was undertaken to see whether CREs could assist pulmonologists (MDs) in managing patients with chronic cough.

METHODS

An 8-week prospective, parallel design, randomized, controlled trial to determine whether CREs using a protocol-driven algorithmic approach could assist in the management of patients referred to a university tertiary care medical center for the assessment and treatment of chronic cough. Patients were randomly assigned to a CRE-led or MD study arm for the management of chronic cough. Patients were screened to exclude those patients whose cough was due to life-threatening conditions. The primary outcome was measured with the cough-specific quality-of-life questionnaire (CQLQ).

RESULTS

A total of 198 patients were randomized, and 8-week results were available on 151 patients (mean [+/- SD] age, 49.8 +/- 13.4 years; female gender, 70%; median cough duration, 16 months). At 8 weeks, total CQLQ scores improved in the CRE-led patients (score [+/- SD] range, 58.1 +/- 14.9 to 50.0 +/- 15.8; p = 0.0003). CQLQ scores improved in four of six domains but not in the physical or emotional domains. Improvements in CRE-led patients were similar to those in MD-managed patients (initial CQLQ score, p = 0.261 [CRE vs MD]; CQLQ score at 8 weeks, p = 0.42 [CRE vs MD]). In a composite analysis of both CRE and MD patient data, CQLQ scores improved in patients whose cough resolved (56.3 +/- 13.6 to 41.5 +/- 13.6; p < 0.0001), in those whose cough improved but did not disappear (60.9 +/- 14.2 to 50.5 +/- 13.9; p < 0.0001), but did not improve in those whose cough did not improve (58.1 +/- 13.3 to 58.6 +/- 12.7; difference not significant).

CONCLUSIONS

CREs can help to safely, economically, and effectively manage properly screened patients with chronic cough. The use of CREs may shorten wait times for specialist consultation for these patients.

Diagnosis and management of premature ventricular complexes-associated chronic cough

BACKGROUND

Chronic cough frequently remains unexplained. Although various cardiac arrhythmias have already been reported as a cause of chronic cough, this phenomenon has not been evaluated prospectively. Therefore, we studied the incidence and management of cough associated with premature ventricular complexes (PVCs) in a population of patients with this condition.

METHODS

Patients without organic heart disease who had been referred for the management of symptomatic PVC were evaluated prospectively. PVC-associated cough was recognized if cough episodes occurred just after spontaneous or induced PVC or observed in an ECG or a multichannel recording system that included ECG. A differential diagnosis of cough was performed according to the guidelines on cough. Afterward, antiarrhythmic therapy was instituted to eliminate PVC and cough.

RESULTS

Of the 120 patients who were referred for the management of PVC, 10 had a chronic cough. After extensive workup for the cause of chronic cough, the cough was thought to be solely due to PVC in one patient, partially due to PVC plus another cause in five patients, and not due to PVC but to nonasthmatic eosinophilic bronchitis, gastroesophageal reflux disease, and chronic sinusitis in four patients. Patients with PVC-associated cough reported more severe perception of symptoms associated with arrhythmia than patients without cough (mean [+/- SD] visual analog scale score, 8.2 +/- 0.5 vs 5.7 +/- 1.6, respectively; p < 0.01). PVC-associated cough disappeared after antiarrhythmic treatment (radiofrequency ablation [n = 4], oral antiarrhythmic agent [n = 1]), or after spontaneous remission of PVC (n = 1).

CONCLUSIONS

PVC may be a cause of chronic cough. Interdisciplinary cooperation is warranted for the proper diagnosis and management of PVC-associated cough.

Habit cough

OBJECTIVE

To review habit cough and its treatments to raise awareness of this condition as a potential cause of chronic cough.

DATA SOURCES

Relevant articles and references published between January 1, 1962, and April 30, 2008, were found through a PubMed search using the following keywords: habit cough, psychogenic cough, chronic cough, and tic cough.

STUDY SELECTION

All key relevant articles were reviewed, and the most relevant were selected for inclusion in this review.

RESULTS

Habit cough is a diagnosis of exclusion and can occur in children and adults with chronic cough. Characteristic features of habit cough include a loud honking or barking cough, disruption of normal activities, and the frequent presence of a secondary gain (such as school absence). Successful treatment has been described in several case reports and involves mostly nonpharmacologic measures.

CONCLUSIONS

It is important to consider habit cough in the differential diagnosis of chronic cough because early diagnosis can help to avoid unnecessary invasive procedures and potential iatrogenic complications.

Assessing response to treatment of exacerbations of bronchiectasis in adults

The present study aimed to assess the effect of intravenous antibiotic therapy on clinical and laboratory end-points in exacerbations of noncystic fibrosis bronchiectasis and to determine whether the outcomes were influenced by the pathogenic organism isolated. A prospective cohort study was conducted from November 2006 to March 2008 of exacerbations requiring intravenous antibiotics. End-points included 24-h sputum volume, forced expiratory volume in one second (FEV(1)), forced vital capacity (FVC), incremental shuttle walk test, qualitative sputum microbiology, white cell count, erythrocyte sedimentation rate, C-reactive protein (CRP) and St George's Respiratory Questionnaire (SGRQ). Exacerbations due to Pseudomonas aeruginosa were compared with exacerbations due to other potential pathogenic organisms. In total, 32 exacerbations were studied. Following 14 days of intravenous antibiotics, all outcomes significantly improved independent of a pathogenic organism, except FEV(1) and FVC. The most responsive markers were: 24-h sputum volume (reduced in all patients and 80% had >/=50% reduction); sputum bacterial clearance (78.1%); CRP (>/=75% reduction in 62.5%) and SGRQ (>/=4 unit improvement in 89.7%). CRP, 24-h sputum volume and SGRQ improved independent of microbial clearance. In the current study, 24-h sputum volume, microbial clearance, C-reactive protein and St George's Respiratory Questionnaire were the most useful parameters to assess response to treatment of exacerbations of bronchiectasis. Outcomes were similar independent of the pathogenic organism with the exception of forced expiratory volume in one second and forced vital capacity.

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.

Eosinophilic airway disorders associated with chronic cough

Chronic cough is a major clinical problem. The causes of chronic cough can be categorized into eosinophilic and noneosinophilic disorders, the former being comprised of asthma, cough variant asthma (CVA), atopic cough (AC) and non-asthmatic eosinophilic bronchitis (NAEB). Cough is one of the major symptoms of asthma. Cough in asthma can be classified into three categories; 1) CVA: asthma presenting solely with coughing, 2) cough-predominant asthma: asthma predominantly presenting with coughing but also with dyspnea and/or wheezing, and 3) cough remaining after treatment with inhaled corticosteroid (ICS) and beta2-agonists in patients with classical asthma, despite control of other symptoms. There may be two subtypes in the last category; one is cough responsive to anti-mediator drugs such as leukotriene receptor antagonists and histamine H1 receptor antagonists, and the other is cough due to co-morbid conditions such as gastroesophageal reflux. CVA is one of the commonest causes of chronic isolated cough. It shares a number of pathophysiological features with classical asthma with wheezing such as atopy, airway hyperresponsiveness (AHR), eosinophilic airway inflammation and various features of airway remodeling. One third of adult patients may develop wheezing and progress to classical asthma. As established in classical asthma, ICS is considered the first-line treatment, which improves cough and may also reduce the risk of progression to classical asthma. AC proposed by Fujimura et al. presents with bronchodilator-resistant dry cough associated with an atopic constitution. It involves eosinophilic tracheobronchitis and cough hypersensitivity and responds to ICS treatment, while lacking in AHR and variable airflow obstruction. These features are shared by non-asthmatic eosinophilic bronchitis (NAEB). However, atopic cough does not involve bronchoalveolar eosinophilia, has no evidence of airway remodeling, and rarely progresses to classical asthma, unlike CVA and NAEB. Histamine H1 antagonists are effective in atopic cough, but their efficacy in NAEB is unknown. AHR of NAEB may improve with ICS within the normal range. Taken together, NAEB significantly overlaps with atopic cough, but might also include milder cases of CVA with very modest AHR. The similarity and difference of these related entities presenting with chronic cough and characterized by airway eosinophilia will be discussed.

Chronic cough – occupational considerations

Chronic cough is a common symptom in a wide range of respiratory conditions, and may also occur as a result of upper airway or gastro-esophageal problems. Whilst chronic cough of any cause may be exacerbated by work, in some cases it has a direct occupational cause, resulting from a harmful acute or chronic workplace exposure. Such occupational conditions may only be suspected by taking a detailed occupational history, and directly asking employed patients whether their cough improves away from work. Early and accurate diagnosis, linked with tailored drug therapy, modification of workplace exposures, and expert compensation advice is likely to offer the best outcome for this group of patients.

Simultaneous versus video counting of coughs in hypertonic cough challenges

Background

The coughs occurring during cough provocation tests are usually counted at the same time when the test is being conducted, i.e., simultaneously. It is unknown whether cough counting from video recording might increase the accuracy of the cough counting. During recent years, cough challenges with hypertonic aerosols have been introduced. They often provoke very frequent coughing which may complicate the simultaneous cough counting.

Objective

To assess whether cough counting from video recording is superior to simultaneous cough counting in two different hypertonic cough challenges.

Methods

The analysis includes 82 hypertonic saline challenges performed on 66 subjects, providing 1984 observation minutes with both simultaneous and video cough counting. The cough sensitivity was expressed as the osmolality to provoke 15 cumulative coughs (CUM15). The analysis also includes 136 hypertonic histamine challenges performed on 114 subjects providing 5373 observation minutes with both simultaneous and video counting. The cough sensitivity was expressed as the cumulative number of coughs divided by the final histamine concentration administered (CCR). This challenge involved several additional measurements to cough counting.

Results

For the saline challenge, the mean difference between the counting types was 0.0 coughs per minute with 95% limits of agreement of -1.2 to 1.2 coughs per minute. For the hypertonic histamine challenge the respective figures were 0.3 (-1.9 to 2.5) coughs per minute. At high coughing frequency the video counts tended to outnumber the simultaneous counts. The counting type had no effect on the hypertonic saline CUM15 and only a marginal effect on its repeatability. On the contrary, video counting resulted to significantly higher hypertonic histamine CCR values than simultaneous counting (p < 0.001).

Conclusion

The agreement between simultaneous and video counting of coughs is generally good. However, as the coughing frequency increases, simultaneous counting may miss coughs, especially if the nurse has to share his/her attention to several activities simultaneously. Video recording is advisable for the hypertonic histamine challenge but unnecessary for the hypertonic saline challenge. To ensure reliable simultaneous cough counting, cough provocation tests should be performed in a quiet environment, applying as little unnecessary equipment and measurements as possible.

Management of chronic cough

Cough that remains unexplained after basic clinical assessment is a common reason for referral to secondary care. Much of the evidence about management of isolated chronic cough is derived from case series; this evidence suggests that isolated chronic cough is usually due to asthma, gastro-oesophageal reflux disease, and upper airway conditions, and that it can be cured in most people by treatment of these conditions. However, there is increasing recognition that satisfactory control of chronic cough is not achieved in a substantial number of patients seen in secondary care. Moreover, there is a concern that perpetuation of the belief that chronic cough is solely due to the effects of comorbid conditions is inhibiting research into the pathophysiology of an abnormally heightened cough reflex, and jeopardising development of improved treatments. We advocate a change in emphasis, which makes a clear distinction between cough due to corticosteroid-responsive eosinophilic airway diseases and corticosteroid-resistant non-eosinophilic cough. We recommend that some factors with weak evidence of an association with cough are best viewed as potential aggravating factors of an intrinsic abnormality of the cough reflex, rather than the cause. We call for more research into the basic mechanisms and pharmacological control of an abnormally heightened cough reflex, and recommend ways to assess the effects of potentially antitussive treatments.

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.

Prevalence of inflammatory bowel disease in patients with airways disease

BACKGROUND

Case reports and case series have suggested an association between inflammatory bowel disease (IBD) and airways disease, but there are no data demonstrating a higher prevalence of IBD among patients with airways disease. Furthermore, no consistent radiological, pulmonary or pathological abnormalities have been demonstrated in patients with both conditions.

AIMS

To determine the prevalence of IBD among patients with airways disease and to evaluate clinical and pathophysiological features.

METHODS

A retrospective analysis of outpatients with airways disease over a 10-year period.

RESULTS

IBD was four times more prevalent among patients with airways disease compared with published local IBD prevalence [Odds Ratio 4.26, 95% CI 1.48, 11.71, p=0.006; Crohn's disease OR 5.96, 95% CI 1.94, 18.31, p=0.002 and ulcerative colitis OR 4.21, 95% CI 1.71, 10.41, p=0.001]. IBD was more frequent in all types of airways disease except asthma; the association was particularly strong for conditions associated with productive cough. All except 1 patient had established IBD before the onset of respiratory symptoms. There were no obvious radiological differences between ulcerative colitis and Crohn's disease cases. There was a trend for a higher lymphocyte count (despite a tendency to lower blood lymphocyte count) but lower sputum neutrophil count in patients with Crohn's disease compared with ulcerative colitis. There were no significant differences in physiological measurements of pulmonary function between the two types of IBD.

CONCLUSION

Our findings support an association between airways disease and inflammatory bowel disease, particularly non-asthmatic airways disease with productive cough.

Pharmacotherapy of cough-variant asthma

Cough-variant asthma is considered as an asthma subset in which chronic cough is the only symptom. It is believed to be more frequent and, hence, sometimes overdiagnosed in children, and shares with typical asthma eosinophilic airway inflammation and consequent bronchial hyper-responsiveness. Presently available therapies consist of bronchodilators, inhaled or oral corticosteroids, or leukotriene modifiers. However, the long-term efficacy of these agents in adults and children is not known. This review focuses on current therapies used for cough variant asthma, also highlighting potential therapeutic targets for this condition.

Therapy Insight: treatment of gastroesophageal reflux in adults with chronic cough

Gastroesophageal reflux (GER) is the second most common cause of chronic cough in immunocompetent patients who are nonsmokers, not on angiotensin-converting-enzyme inhibitors and have normal chest radiographs. Identification of GER in chronic cough patients can be difficult; most patients with GER-related cough have no esophageal symptoms and no esophageal test is adequate to make this diagnosis. Post-hoc analysis of four prospective intervention trials has identified a clinical patient profile that can predict the presence of GER-related cough 91% of the time. Clinical practice guidelines from the American College of Chest Physicians and the British Thoracic Society recommend initiating an initial empiric GER therapy trial, with esophageal testing being reserved for nonresponders. The empiric trial should include conservative measures and PPIs twice daily for 3 months. Selected patients who have dysphagia might benefit from the addition of a prokinetic agent. Esophageal manometry and pH testing with impedance monitoring (if available) should be performed in nonresponders while they are on therapy. It can take more than 50 days for cough to respond to medical GER therapy. Surgical fundoplication might be helpful in very carefully selected patients. Careful evaluation and treatment resolves cough in approximately 80% of patients with GER-related cough.

New developments in the objective assessment of cough

A variety of different methods are available for measuring cough. In clinical practice and most clinical trials subjective reporting of cough is relied upon, using scoring systems or visual analog scores (VAS). Although these measures give an indication of patients' perceptions of the severity of the symptom, they may be unreliable because they are influenced by other factors such as mood, vigilance, and expectations. An objective measure of cough would therefore be a valuable tool. In the last decade advances in computer technology and the availability of portable digital sound recording devices have resulted in a resurgence of interest in developing ambulatory systems for recording cough. The ultimate goal is an automated detection system of use in the wide variety of conditions that cause cough. Multidisciplinary teams of researchers around the world are applying techniques such as neural networks, voice recognition models, and other signal processing techniques to this problem. The main challenge is achieving high sensitivity with good discrimination of noncough signals. For cough sound detection, this is confounded by both the variability of the acoustics of cough sounds within and between individuals and the amount and variety of speech sounds that must be discriminated. Significant progress is being made and it is likely that accurate automated objective monitoring systems will be available in the near future. These systems have the potential to change the way cough is measured in clinical practice and clinical trials, allowing a better understanding of the effect of existing and novel treatments on this troublesome symptom.

Does idiopathic cough exist?

Despite a meticulous protocol involving diagnostic testing and trials of empirical therapy, there may be no obvious cause for a chronic cough in up to 42% of cases referred for specialist evaluation. In some cases, failure to consider causes that include the asthma/eosinophilic airway syndromes such as eosinophilic bronchitis and atopic cough, or nonacid gastroesophageal reflux disease may explain diagnostic failure. However, a distinct group of patients may be considered to have true idiopathic cough. Current published evidence suggests a certain patient phenotype, namely, middle-aged females with prolonged nonproductive cough and cough reflex hypersensitivity. Almost nothing else is known about this clinical entity and currently no specific therapy exists.

Use of exhaled nitric oxide in predicting response to inhaled corticosteroids for chronic cough

OBJECTIVE

To evaluate our experience with patients who presented with chronic cough and how exhaled nitric oxide predicted response to inhaled corticosteroid (ICS) therapy.

PATIENTS AND METHODS

This retrospective observational study of 114 patients evaluated for chronic cough with measured exhaled nitric oxide and methacholine challenge testing was conducted from December 1, 2004, through November 30, 2005. Clinical records were extracted. Patients with no documented follow-up were contacted by telephone and administered a questionnaire.

RESULTS

In 64 patients, ICS therapy was started or the current ICS dose increased. Forty-one patients had elevated exhaled nitric oxide levels (defined as >or=35 ppb), 36 (88%) of whom had significant improvement in their chronic cough (likelihood ratio of a positive response, 4.9; 95% confidence interval, 2.2-10.9). Twenty-three patients with exhaled nitric oxide levels in the reference range were also prescribed ICS, and only 2 had cough improvement (likelihood ratio of a negative response, 0.07; 95% confidence interval, 0.02-0.25). Patients had documented follow-up that ranged from 4 weeks to 16 months. A cutoff of 38 ppb was found to best differentiate ICS responders and nonresponders.

CONCLUSIONS

Measurement of exhaled nitric oxide accurately predicted response to ICS therapy for chronic cough. Patients with a positive exhaled nitric oxide test result had a strong likelihood of response to ICS, whereas a negative exhaled nitric oxide test result indicated an unlikely response to ICS. This finding may potentially have an impact on how patients with chronic cough are evaluated and treated.

Atopic features of cough variant asthma and classic asthma with wheezing

BACKGROUND

Cough variant asthma is a phenotype of asthma solely presenting with coughing. It involves airway inflammation and remodelling as does classic asthma with wheezing, and a subset of patients may progress to classic asthma. The atopic features of cough variant asthma remain unclear.

OBJECTIVE

To compare atopic features between patients with cough variant asthma and those with classic asthma, and to examine the possible correlation of these features with the future development of wheezing in the former group.

METHODS

Total and specific IgE levels of seven common aeroallergens [house dust mite (HDM), Gramineae/Japanese cedar/weed pollens, moulds, cat/dog dander] were examined in 74 cough variant asthma patients and in 115 classic asthma patients of varying severity. Forty of the former patients were prospectively observed for 2 years to determine whether cough variant asthma progressed to classic asthma despite inhaled corticosteroid treatment.

RESULTS

Patients with classic asthma had higher total IgE (P<0.0001), larger numbers of sensitized allergens (P=0.03), and higher rates of sensitization to dog dander (24% vs. 3%, P<0.0001), HDM (46% vs. 28%, P=0.02), and moulds (17% vs. 7%, P=0.047) than did patients with cough variant asthma. Wheezing developed in six (15%) patients with cough variant asthma, who were sensitized to larger numbers of allergens (P=0.02) and had higher rates of sensitization to HDM (P=0.01) and dog dander (P=0.02) than the 34 patients in whom wheezing did not develop. Among the patients with classic asthma, total and specific IgE variables were similar in the subgroup with mild disease (n=60) and the subgroup with moderate-to-severe disease (n=55), as reported previously.

CONCLUSIONS

Atopy may be related to the development of wheezing in patients with cough variant asthma. To prevent the progression of cough variant asthma to classic asthma, avoidance of relevant allergens may be essential.

Before we get started: what is a cough?

Cough is an airway defensive reflex consisting of an inspiratory phase followed by a forced expiratory effort initially against a closed glottis, followed by active glottal opening and rapid expiratory flow. The expiration reflex (ER) differentiates from cough for the lack of a preparatory inspiration. The reflexes subserve different functions: cough will clear the lower airways from debris and mucus, while the expiration reflex will prevent aspiration. Clinically, a cough epoch is a sequence of motor acts resulting from a combination of true coughs and ERs that need to be accurately identified and measured for adequate quantitative description.

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.

What is cough and what should be measured?

Cough is usually defined as a three-phase event, although for convenience clinicians may prefer to define it as only the expiratory expulsive efforts. Cough may occur as a single event or as a cough 'epoch' (or 'bout' or 'attack') that includes several or many expiratory efforts in a single episode. The distinction between a single cough and a cough epoch is important, both in mechanistic and clinical implications, since the latter may include many 'expiration reflexes' (ERs), for which the functions and neural mechanisms are different from those of the cough reflex. We describe the various ways in which cough can be assessed. For simplicity in clinical work the main methods are patient scores or automated cough counters; these assess only one aspect of the complex changes in cough. For analytical and basic medical studies other facets of cough need to be included: expiratory EMGs, respiratory pressures, airflows and lung volume changes. Cough 'intensity', a much used expression, needs to be defined in terms of the facets of cough which are being measured.

Taming chronic cough

OBJECTIVE

To review the available evidence on treating chronic cough to relay a thoughtful, evidence-based approach for the diagnosis and treatment of chronic cough.

DATA SOURCES

MEDLINE, PubMed, EMBASE, and CINAHL were searched using the following keywords: cough, asthma, gastroesophageal reflux, sinusitis, rhinitis (allergic, seasonal), postnasal drip, vocal cord dysfunction, lung disease (interstitial), bronchiectasis, and bronchoscopy.

STUDY SELECTION

Studies were selected based on their relevance to the diagnosis and treatment of chronic cough. Because of a lack of randomized prospective studies, nonrandomized and retrospective studies were considered, with their strengths and limitations noted.

RESULTS

Few randomized controlled trials have addressed the diagnosis and treatment of chronic cough. There are several prospective noncontrolled trials for adults with chronic cough that found a high percentage of cough resolution when using an approach that focused on the diagnosis and treatment of the most common causes: asthma, gastroesophageal reflux disease, and upper airway cough syndrome. Preliminary studies in children support an approach that distinguishes between a wet and dry cough, as well as an in-depth investigation of any specific symptoms that point to an underlying chronic illness.

CONCLUSION

Allergists, as experts in treating upper airway and lower airway disorders, are uniquely poised to diagnose and treat chronic cough.

Defining the relationship between gastroesophageal reflux and cough: probabilities, possibilities and limitations

The common co-existence of cough and gastroesophageal reflux disease (GORD) is well established. However, ascertaining cause and effect is more difficult for many reasons that include occurrence by chance of two common symptoms, the changing definition of GORD, equipment limitations and the lack of randomised controlled trials. Given these difficulties, it is not surprising that there is disparity of opinion between respiratory and gastroenterology society guidelines on the link between GORD and chronic cough. This commentary explores of these issues.

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.

Geography and cough aetiology

Cough is the most common complaint that leads patients to seek medical attention. Especially chronic persistent cough is annoying, and requires appropriate diagnosis and treatment. Recent cough guidelines and original papers on cough epidemiology from various countries show remarkable differences in the aetiology of chronic cough among countries, especially between US, UK and Japan. Entities associated with rhinosinus disease (post-nasal drip/upper airway cough syndrome reported from the US, rhinitis or rhinosinusitis from the UK, and sinobronchial syndrome from Japan), and eosinophilic lower airway disorders (cough variant asthma, non-asthmatic eosinophilic bronchitis and atopic cough) are most confusing and might involve significant overlap. In this article, issues related to chronic cough aetiology are discussed, including geographic issues, e.g. 'simple' geography or difference in race, and difference in patient characteristics possibly arising from difference in the medical system.

Comparative Efficacy and Tolerability of Pholcodine and Dextromethorphan in the Management of Patients with Acute, Non-Productive Cough

INTRODUCTION

The aim of this study was to compare the efficacy and tolerability of pholcodine with that of dextromethorphan, one of the most used cough sedative products, in patients with acute, non-productive cough.

METHODS

129 adults with a diagnosis of acute, frequent, non-productive cough participated in a randomized, double-blind, parallel-group, multicenter trial. Medications were in a syrup formulation and were taken orally three times daily for 3 days. The efficacy endpoints were the change from baseline in the daytime and night-time cough frequency on 5-point scales at day 3, and cough intensity.

RESULTS

A reduction of 1.4 and 1.3 points in the mean daytime cough frequency at day 3 was seen in the pholcodine and dextromethorphan groups, respectively, in the per-protocol population. The reduction in mean night-time cough was 1.3 for both groups. Cough intensity reduction was 0.7 for pholcodine and 0.8 for dextromethorphan.

CONCLUSIONS

These findings indicate that the efficacy of a 3-day course of pholcodine is similar to that of dextromethorphan in the treatment of adult patients with acute, non-productive cough. Both medications were well tolerated.