Prevalence, pathogenesis, and causes of chronic cough

Does gastroesophageal reflux scintigraphy correlate with clinical findings in children with chronic cough?

OBJECTIVE

Gastroesophageal reflux (GER), a common problem during childhood, leads to chronic troublesome symptoms including chronic respiratory symptoms. Therefore, timely diagnostic work-up for GER is essential in children when GER is suspected. In this study, we aimed to establish whether scintigraphic parameters have clinical importance in investigating the reflux in children.

METHODS

A total of 72 children older than 7 years with chronic cough of unknown etiology were enrolled for this study. The scintigraphic procedure was performed by using technetium-99m tin colloid (37-74 MBq). Cough and GER scores were used for children who were positive for GER both before and after GER treatment.

RESULTS

Of 72 children, 65 children with a mean age of 10.3+/-2.3 (7-19) years had GER on gastroesophageal scintigraphy. Median reflux episode number was 7 (1-14). There was a significantly positive correlation between reflux episode number and cough (r = 0.446, P<0.001) and GER score (r = 0.432, P<0.001). The significant decrease was observed in cough (from 3.5+/-1.9 to 1.6+/-1.3) and GER scores (from 4.1+/-2.5 to 1.3+/-1.1) with GER treatment (P<0.001 for each).

CONCLUSION

Scintigraphy should be used for the detection of GER in children who present with chronic cough. Increasing episode number in gastroesophageal scintigraphy might be a predictor for reflux-related symptom severity.

The cough hypersensitivity syndrome: a novel paradigm for understanding cough

For many years patients with chronic cough have been investigated in an attempt to diagnose the cause of the cough. Here I suggest that the overwhelming majority of patients with chronic cough have a single diagnosis: cough hypersensitivity syndrome. This is demonstrated by the homogeneous nature of the clinical history and investigational results of patients attending cough clinics. The hypersensitivity facet of the syndrome is demonstrated by objective testing with capsaicin and other protussive agents. Within the cough hypersensitivity syndrome there are different phenotypes. Those patients with a predominantly Th2-type immune response will develop eosinophilic inflammation and either cough-variant asthma or eosinophilic bronchitis. Those with predominantly heartburn symptoms will have a phenotype that reflects GERD and cough. However, the similarities between the different phenotypes far outweigh differences in a unifying diagnosis of the cough hypersensitivity syndrome, providing a more rational understanding of chronic cough.

Cough reflex is additively potentiated by inputs from the laryngeal and tracheobronchial [corrected] receptors and enhanced by stimulation of the central respiratory neurons

The cough is an essential airway defense reflex. In this study we investigated the coordination of inputs from the laryngeal and tracheobronchial receptors in the cough reflex. In 15 beagle dogs (7-9 kg) lightly anesthetized with intravenous profobol (20-30 mg/kg/h), the cough response was elicited with mechanical stimulation of either the vocal chord or tracheal bifurcation. Simultaneous stimulation of both sites increased all the parameters of cough strength, that is, mean pleural pressure (P (pl)), mean expiratory flow, number of cough bouts, and cough duration, in comparison with stimulation of the sites individually. The increases in mean P (pl) and cough duration reached statistical significance (13.3 vs. 18.4 cmH(2)O and 13.3 vs. 18.2 s, respectively). When the anesthetic level became deeper, the prolongation of cough duration almost disappeared, but the augmentation of mean P (pl) was much less affected. During stimulation of the central respiratory neurons by intravenous dimorphoramine or acute hyperoxic hypercapnia, the cough strength increased significantly. We concluded that inputs from the laryngeal and tracheobonchial cough receptors acted in concert and potentiated the cough reflex. Furthermore, stimulation of the central respiratory neurons may increase the intensity of a cough response.

Prostanoid receptor antagonists: development strategies and therapeutic applications

Identification of the primary products of cyclo-oxygenase (COX)/prostaglandin synthase(s), which occurred between 1958 and 1976, was followed by a classification system for prostanoid receptors (DP, EP(1), EP(2) ...) based mainly on the pharmacological actions of natural and synthetic agonists and a few antagonists. The design of potent selective antagonists was rapid for certain prostanoid receptors (EP(1), TP), slow for others (FP, IP) and has yet to be achieved in certain cases (EP(2)). While some antagonists are structurally related to the natural agonist, most recent compounds are 'non-prostanoid' (often acyl-sulphonamides) and have emerged from high-throughput screening of compound libraries, made possible by the development of (functional) assays involving single recombinant prostanoid receptors. Selective antagonists have been crucial to defining the roles of PGD(2) (acting on DP(1) and DP(2) receptors) and PGE(2) (on EP(1) and EP(4) receptors) in various inflammatory conditions; there are clear opportunities for therapeutic intervention. The vast endeavour on TP (thromboxane) antagonists is considered in relation to their limited pharmaceutical success in the cardiovascular area. Correspondingly, the clinical utility of IP (prostacyclin) antagonists is assessed in relation to the cloud hanging over the long-term safety of selective COX-2 inhibitors. Aspirin apart, COX inhibitors broadly suppress all prostanoid pathways, while high selectivity has been a major goal in receptor antagonist development; more targeted therapy may require an intermediate position with defined antagonist selectivity profiles. This review is intended to provide overviews of each antagonist class (including prostamide antagonists), covering major development strategies and current and potential clinical usage.

The management of cough: a clinical year in review

As the number of published articles in the field of cough increases year on year, it is sometimes helpful to pause and review what might have passed us by. This "Clinical Year in Review" provides an opportunity to reflect on a number of important studies reported in the area of both adult and pediatric cough. It would be impossible to cover all the important published literature; therefore, this effort has been confined to selected topics published in the last 12 months with direct relevance to the clinical management, measurement, and treatment of cough. While this article reflects a personal commentary of the literature, it is hoped that it will contribute to improving "evidence-based" care for the many individuals burdened with a troublesome cough.

Rhinosinusitis, laryngopharyngeal reflux and cough: an ENT viewpoint

Chronic cough is a common presentation. Postnasal drip (PND) and gastro-oesophageal reflux are mostly implicated in the aetiology. Directly examining the larynx can often help to demonstrate laryngitis or inter-arytenoid oedema that is mostly attributed to reflux. Although "the syndrome of postnasal drip" is considered as a major cause for chronic cough, evidence of its existence is mostly difficult to elicit on examination. Furthermore, the majority of patients with "postnasal drip" seen in ENT outpatients do not complain of cough. Evidence does suggest there is a link between postnasal drip and cough. The fact that some patients present with cough in association with this syndrome and others do not is still not well understood.

Cough and viruses in airways disease: mechanisms

Acute cough is a major symptom of viral respiratory tract infection and causes excessive morbidity in human populations across the world. A wide variety of viruses play a role in the development of cough after acute infection and all of these manifest a similar clinical picture across different age groups. Despite the large disease burden surprisingly little is known about the mechanism of acute cough following viral infection. Both in vitro and in vivo experiments show that increased production of neuropeptides and leukotrienes mediate cough after viral infection, along with altered expression of neural receptors. Increased airway mucus production is also likely to play a significant role. This work is reviewed in this article.

Following the recent development of a mouse model for rhinovirus infection and the establishment of experimental models of rhinovirus challenge in human subjects with both asthma and COPD the field is expanding to translate in vitro research into clinical studies and hopefully eventually into clinical practice. Developing a clearer understanding of the mechanisms underlying virus induced cough may lead to more specific and effective therapies.

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.

Expression of transforming growth factor-beta (TGF-beta) in chronic idiopathic cough

In patients with chronic idiopathic cough, there is a chronic inflammatory response together with evidence of airway wall remodelling and an increase in airway epithelial nerves expressing TRPV-1. We hypothesised that these changes could result from an increase in growth factors such as TGFbeta and neurotrophins. We recruited 13 patients with persistent non-asthmatic cough despite specific treatment of associated primary cause(s), or without associated primary cause, and 19 normal non-coughing volunteers without cough as controls, who underwent fiberoptic bronchoscopy with bronchoalveolar lavage (BAL) and bronchial biopsies. There was a significant increase in the levels of TGFbeta in BAL fluid, but not of nerve growth factor(NGF) and brain-derived nerve growth factor(BDNF) compared to normal volunteers. Levels of TFGbeta gene and protein expression were assessed in bronchial biopsies. mRNA expression for TGFbeta was observed in laser-captured airway smooth muscle and epithelial cells, and protein expression by immunohistochemistry was increased in ASM cells in chronic cough patients, associated with an increase in nuclear expression of the transcription factor, smad 2/3. Subbasement membrane thickness was significantly higher in cough patients compared to normal subjects and there was a positive correlation between TGF-beta levels in BAL and basement membrane thickening. TGFbeta in the airways may be important in the airway remodelling changes observed in chronic idiopathic cough patients, that could in turn lead to activation of the cough reflex.

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.

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.

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.

Mechanisms of the cough associated with rhinosinusitis

The diseases of the nose and paranasal sinuses (rhinosinusitis) often in combination with asthma and gastroesophageal reflux are common causes of chronic cough in patients with normal chest radiograph. The relationships between rhinosinusitis and cough are incompletely understood. We investigated modulation of the cough reflex by the inputs from the nose. We demonstrate that the cough reflex is sensitized by the intranasal administration of sensory nerve activators in animal models and in humans. Cough reflex is also sensitized in the guinea pig model of allergic nasal inflammation and in patients with allergic rhinitis. In patients with allergic rhinitis the cough sensitization is augmented during the allergen season. We conclude that the cough reflex can be sensitized from the nose. Our data indicate that this sensitization is mediated by nasal sensory nerves. We speculate that by inducing the cough reflex sensitization rhinosinusitis contributes to chronic cough. If combined with environmental or endogenous cough triggers, the cough reflex sensitization is predicted to cause excessive coughing. The potential endogenous cough triggers may be associated with rhinosinusitis (postnasal drip, aspiration of nasal secrets) or secondary to a coexistent disease such as asthma or gastroesophageal reflux.

Speech pathology for chronic cough: a new approach

Chronic cough may persist despite systematic evaluation and medical treatment of known associated diseases such as asthma, rhinitis, and gastro-esophageal reflux. These patients have refractory chronic cough and many exhibit laryngeal hypersensitivity that is manifest at both a sensory and motor level. Examples of this are heightened sensitivity of the cough reflex to capsaicin, and laryngeal motor dysfunction with hoarse vocal quality and paradoxical vocal cord movement. Chronic cough that persists despite medical treatment may respond to speech pathology intervention. A multidimensional speech pathology treatment programme was designed based upon methods used to treat hyperfunctional voice disorders and paradoxical vocal fold movement. This included education, vocal hygiene training, cough suppression strategies and psychoeducational counseling. When tested in a single-blind, randomized, placebo-controlled trial involving 87 patients, participants in the treatment group demonstrated a significant reduction in cough, breathing, voice and upper airway symptoms following intervention, as well as improvements in auditory perceptual ratings of voice quality (breathy, rough, strain and glottal fry) and significant improvement in voice acoustic parameters (maximum phonation time, jitter and harmonic-to-noise ratio). Speech pathology intervention can be an effective way to treat refractory chronic cough.

Chronic cough and tonsillar hypertrophy: a case series

Two patients with intractable chronic cough were found to have tonsillar tissue impinging on their epiglottis. In both case, tonsillectomy was curative. The observations in these patients are consistent with a previous report indicating chronic cough from the uvula in contact with the epiglottis with cough cessation following uvulectomy.

Respiratory symptoms among residents of a heavy-industry province in China: prevalence and risk factors

OBJECTIVE

In China, significant levels of environmental pollution, substandard worksite quality and high rates of smoking predispose the population to potentially high risks of respiratory illnesses and other diseases. We assessed the prevalence of respiratory symptoms and their risks in relation to personal, occupational and environmental risk factors in a heavy-industry province of northeastern China.

METHODS

Lifestyle, health, residential and occupational data were obtained in 2002 from 31,704 adults of six cities in Liaoning, China, using self-assessment questionnaires. General linear and multi-level models were used to evaluate prevalence rates and risks of respiratory symptoms, related to both individual and combined exposures to environmental and occupational risk factors.

RESULTS

The crude prevalence rates (PRs) for persistent cough, persistent phlegm, wheeze and asthma were 2.3, 3.8, 2.1 and 1.0%, respectively. The odds ratios (ORs) of all four respiratory symptoms examined were increased by: smoking (ORs from 2.06 to 5.02), occupational dust (ORs from 1.35 to 1.72), occupational gas (ORs from 1.48 to 1.72) and presence of irritating smoke during cooking (ORs from 1.54 to 2.22). An index combining proximity of residence to road, factory or chimney, indoor coal use and presence of irritating smoke during cooking was associated with up to 3.9-fold increased risks of all symptoms. Increasing values of each risk factor were generally associated with dose-response trends in prevalence rates and risks (all p for trend <0.01).

CONCLUSION

The crude PRs of symptoms were lower than those reported by European and American studies but closer to those of previous Chinese studies. The risks of respiratory symptoms in this population were increased by smoking, occupational exposures to dust and gas, and combined residence-related exposures such as living close to a main road, factory or chimney, indoor coal use and the presence of irritating smoke during cooking, among other risk factors.

Acute bronchitis and volcanic air pollution: a community-based cohort study at Kilauea Volcano, Hawai'i, USA

Eruption at Kilauea Volcano, Hawai'i, has continued since 1983, emitting sulfurous air pollution into nearby communities. The purpose of this cohort study was to estimate the relative risk (RR) of acute bronchitis over a period from January 2004 to December 2006 in communities exposed to the volcanic air pollution. A community-based case review was conducted using medical records from clinics and emergency rooms in exposed and unexposed study areas. Initial visits by local residents for diagnosed acute bronchitis were clinically reviewed. The cumulative incidence rate for the 3-yr period was 117.74 per 1000 in unexposed communities and 184.63 per 1000 in exposed communities. RR estimates were standardized for age and gender, revealing an elevated cumulative incidence ratio (CIR) of 1.57 (95% CI = 1.36-1.81) for acute bronchitis in the exposed communities. Highest risk [CIR: 6.56 (95% CI = 3.16-13.6)] was observed in children aged 0-14 yr who resided in the exposed communities. Exposed middle-aged females aged 45-64 yr had double the risk for acute bronchitis than their unexposed counterparts. These findings suggest that communities continuously exposed to sulfurous volcanic air pollution may have a higher risk of acute bronchitis across the life span.