Chronic cough hypersensitivity syndrome

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome: a neurogenic cough prototype

Chronic cough is a frequent disorder that is defined by cough of more than 8 weeks duration. Despite extensive investigation, some patients exhibit no aetiology and others do not respond to specific treatments directed against apparent causes of cough. Such patients are identified as having unexplained or refractory chronic cough. Recently, a high proportion of patients with chronic cough in the context of cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) was highlighted. CANVAS is a rare neurological disorder with a biallelic variation in the replication factor C subunit 1 (RFC1) gene corresponding mostly to an intronic AAGGG repeat expansion. Chronic cough in patients with CANVAS shares similar characteristics with cough hypersensitivity syndrome. The high prevalence of chronic cough in CANVAS gives the opportunity to better understand the neurogenic mechanism of chronic cough. In this review, we will describe the characteristics and mechanisms of CANVAS. We will also address the potential mechanisms responsible for chronic cough in CANVAS. Finally, we will address chronic cough management in the context of CANVAS.

Profile of cough triggers and their relationship with capsaicin cough sensitivity in chronic cough

BACKGROUND

Cough hypersensitivity is an important part of the neurophysiology of cough, which presents with increased cough response to a lower level of stimuli or triggers. Classification of stimuli might bring about additional insight into the underlying mechanisms and management.

OBJECTIVES

This study investigated the profile of cough triggers in chronic cough patients and their relationship with capsaicin cough sensitivity.

DESIGN

This was a cross-sectional observational study.

METHODS

We enrolled patients with different causes of chronic cough from 2006 to 2021. Cough triggers were defined as cough response to chemical triggers, mechanical triggers, meal triggers, or thermal trigger. Cough sensitivity to capsaicin was evaluated by the capsaicin challenge test, which was expressed as the lowest concentration of capsaicin inducing 5 or more coughing (C5).

RESULTS

Among 1211 patients with chronic cough, 1107 (91.4%) patients reported at least one cough trigger. Chemical triggers (66.9%) were the most common cough triggers, followed by thermal exposure (50.6%), mechanical triggers (48.2%), and meal triggers (21.2%). There was no difference in the proportion of chemical triggers among different etiologies. Patients with refractory chronic cough reported the highest prevalence of cough triggers (97.1%). A higher number of meal triggers (34.9%) was associated with gastroesophageal reflux-related cough, and meal triggers and mechanical triggers were more common in refractory chronic cough. Among 254 patients who completed capsaicin challenge test, both the number of total triggers and the number of chemical triggers had a significant but mild correlation with capsaicin cough sensitivity.

CONCLUSION

Cough hypersensitivity as reflected by a variety of cough triggers is a common feature in chronic cough patients, but different etiologies present specific profiles of cough triggers, which could not be evaluated comprehensively by capsaicin cough sensitivity.

[Chronic cough]

Chronic cough (i.e., cough lasting >8 weeks) has a global prevalence of approximately 10%. The individual burden can be long-lasting, with some patients experiencing cough for many years. Although chronic cough is often a symptom of respiratory diseases (e.g., lung cancer, tuberculosis, chronic obstructive pulmonary disease) or associated with triggers (e.g., asthma, gastroesophageal reflux disease, rhinosinusitis) and may resolve after targeted treatment of these conditions, some patients continue to cough despite optimal treatment (refractory chronic cough, RCC) or have no identifiable conditions presumed to be contributing to the cough (unexplained chronic cough, UCC). In patients with chronic cough, it is critical to perform a thorough initial patient assessment with adherence to a diagnostic algorithm (e.g., of the German Respiratory Society Cough Guidelines) to identify the cause of the symptom cough and provide appropriate treatment; or diagnose RCC and UCC. Primary care physicians should provide the initial diagnostic workup of patients with chronic cough (history, physical exam, chest X-ray and spirometry). If no cause of the cough can be identified, referral to specialists (e.g., pulmonologists, gastroenterologists, otolaryngologists) may be appropriate. Increased appreciation of chronic cough as a distinct condition, rather than as only a symptom of other diseases, may help overcome current challenges in diagnosing and managing chronic cough.

Modification of oestrogen signalling pathways influences cough induced by citric acid but not capsaicin in the animal model of both sexes

To clarify the role of oestrogen signalling and the role of oestrogen receptor alpha (ERα) in the cough pathways we performed a study in which coughing was observed in both sexes animal models after the treatment by selective ERα degrader fulvestrant (ICI 182-780) and inhibitor of oestrogen synthesis danazol. Degradation of ERα with the normal plasma oestrogen levels induced by fulvestrant, significantly augments the cough response of female but not male guinea pigs. These changes were observed in citric acid-induced cough. Female guinea pigs responded with an increased count of cough expulsions per challenge time and we also detected shorter cough latency. The capsaicin-induced cough did not change. A similar response was observed after danazol treatment, which decreased the plasma oestrogen level. Our results indicate that the transient receptor potential vanilloid-1 (TRPV1) channel-mediated cough is resistant to the hypoestrous state, while the citric acid-mediated cough is oestrogen-dependent and hypersensitive during the hypoestrous state.

Development of a natural language processing algorithm to detect chronic cough in electronic health records

BACKGROUND

Chronic cough (CC) is difficult to identify in electronic health records (EHRs) due to the lack of specific diagnostic codes. We developed a natural language processing (NLP) model to identify cough in free-text provider notes in EHRs from multiple health care providers with the objective of using the model in a rules-based CC algorithm to identify individuals with CC from EHRs and to describe the demographic and clinical characteristics of individuals with CC.

METHODS

This was a retrospective observational study of enrollees in Optum's Integrated Clinical + Claims Database. Participants were 18-85 years of age with medical and pharmacy health insurance coverage between January 2016 and March 2017. A labeled reference standard data set was constructed by manually annotating 1000 randomly selected provider notes from the EHRs of enrollees with ≥ 1 cough mention. An NLP model was developed to extract positive or negated cough contexts. NLP, cough diagnosis and medications identified cough encounters. Patients with ≥ 3 encounters spanning at least 56 days within 120 days were defined as having CC.

RESULTS

The positive predictive value and sensitivity of the NLP algorithm were 0.96 and 0.68, respectively, for positive cough contexts, and 0.96 and 0.84, respectively, for negated cough contexts. Among the 4818 individuals identified as having CC, 37% were identified using NLP-identified cough mentions in provider notes alone, 16% by diagnosis codes and/or written medication orders, and 47% through a combination of provider notes and diagnosis codes/medications. Chronic cough patients were, on average, 61.0 years and 67.0% were female. The most prevalent comorbidities were respiratory infections (75%) and other lower respiratory disease (82%).

CONCLUSIONS

Our EHR-based algorithm integrating NLP methodology with structured fields was able to identify a CC population. Machine learning based approaches can therefore aid in patient selection for future CC research studies.

Efficacy and Safety of Ojeok-San Plus Saengmaek-San for Gastroesophageal Reflux-Induced Chronic Cough: A Pilot, Randomized, Double-Blind, Placebo-Controlled Trial

Introduction: Gastroesophageal reflux-induced chronic cough (GERC) is one of the most common etiologies of chronic cough. Despite the growing prevalence and interest in GERC, no effective treatment is currently available. In our study, we used a combination of herbal medicines, Ojeok-san (OJS) plus Saengmaek-san (SMS), for the treatment of GERC. Methods: We conducted a pilot, randomized, placebo-controlled, parallel-arm, single-center clinical trial to assess the feasibility of our study protocol, as our study is the first herbal medicine trial for GERC. All enrolled participants were randomly assigned to either the intervention or placebo group in a 1:1 ratio and were administered trial drugs three times a day for 6 weeks, with an evaluation visit performed every 2 weeks for their efficacy and safety assessment until the follow-up visit (week 8). We evaluated the severity and frequency of cough, cough-specific quality of life, airway hypersensitivity, and reflux-related gastrointestinal symptoms, as well as pattern identification, to investigate the complex mechanisms of reflux cough syndrome. Results: A total of 30 participants were enrolled, and 25 completed the study at Kyung Hee University Korean Medicine Hospital from 26 December 2018 to 31 May 2021. OJS plus SMS significantly improved the cough diary score (CDS), cough visual analog scale, Korean version of the Leicester Cough Questionnaire, Hull Airway Reflux Questionnaire, and Gastrointestinal Symptom Rating Scale after the treatment compared to the baseline. Notably, OJS plus SMS showed significant efficacy in the daytime and total CDS compared with the placebo. Only one adverse event was observed during the trial, and no serious adverse events occurred. Additionally, we achieved successful results in feasibility outcomes by exceeding the ratio of 80%. Conclusion: We confirmed the feasibility of our trial design and demonstrated the potential of OJS plus SMS in relieving the severity of cough and GI symptoms in GERC patients with safe and successful feasibility results. We anticipate that our study results will be used as the basis for further large-scale, well-designed, confirmatory trials to evaluate the safety and efficacy of OJS plus SMS in GERC. Clinical Trial Registration: [https://cris.nih.go.kr], identifier WHO International Clinical Trials Registry Platform, Clinical Research Information Service [KCT0003115].

Cough desensitization treatment: A randomized, sham-controlled pilot trial for patients with refractory chronic cough

BACKGROUND

The purpose of this study was to determine feasibility of treating refractory chronic cough (RCC) with progressive doses of capsaicin paired with cough suppression.

METHODS

In this sham-controlled, parallel RCT, 14 adults with RCC were randomly assigned to either behavioral cough suppression therapy (BCST) plus 6 treatment sessions involving exposure to nebulized capsaicin in progressively larger concentrations while actively suppressing cough (n = 8), or BCST plus 6 sessions of exposure to a single subthreshold dose of capsaicin (sham; n = 6). The Leicester Cough Questionnaire (LCQ) was the primary outcome measure. Urge-to-cough (UTC) testing, measuring both UTC and cough frequency, served as secondary outcome measures. Data was analyzed with mixed effects linear regression and follow-up contrasts.

RESULTS

Results on all measures favored the treatment group; however, there was only strong evidence of a difference in treatment effect on cough frequency during UTC testing. Mean change in LCQ at 3-weeks post treatment was 2.95 and 1.75 (p = .23), in the treatment and sham groups, respectively. Cough frequency during UTC testing reduced by 97% and 56% (p < .0001) at three weeks post, respectively. Within-group comparisons revealed strong evidence of change in the treatment group (p < .001) and moderate evidence of a change in the sham group (p = .08) in LCQ.

CONCLUSIONS

Conclusions from this study are limited due to the very small sample size; however, the study provides feasibility and proof-of-concept evidence to support further investigation of treating RCC with repeated exposure to nebulized capsaicin paired with BCST.

Chronic cough: new insights and future prospects

Chronic cough is defined in adults as a cough that lasts for ≥8 weeks. When it proves intractable to standard-of-care treatment, it can be referred to as refractory chronic cough (RCC). Chronic cough is now understood to be a condition of neural dysregulation. Chronic cough and RCC result in a serious, often unrecognized, disease burden, which forms the focus of the current review.The estimated global prevalence of chronic cough is 2-18%. Patients with chronic cough and RCC report many physical and psychological effects, which impair their quality of life. Chronic cough also has a significant economic burden for the patient and healthcare systems. RCC diagnosis and treatment are often delayed for many years as potential treatable triggers must be excluded first and a stepwise empirical therapeutic regimen is recommended.Evidence supporting most currently recommended treatments is limited. Many treatments do not address the underlying pathology, are used off-label, have limited efficacy and produce significant side-effects. There is therefore a significant unmet need for alternative therapies for RCC that target the underlying disease mechanisms. Early clinical data suggest that antagonists of the purinergic P2X3 receptor, an important mediator of RCC, are promising, though more evidence is needed.

WAO-ARIA consensus on chronic cough - Part 1: Role of TRP channels in neurogenic inflammation of cough neuronal pathways

BACKGROUND

Cough features a complex peripheral and central neuronal network. The function of the chemosensitive and stretch (afferent) cough receptors is well described but partly understood. It is speculated that chronic cough reflects a neurogenic inflammation of the cough reflex, which becomes hypersensitive. This is mediated by neuromediators, cytokines, inflammatory cells, and a differential expression of neuronal (chemo/stretch) receptors, such as transient receptor potential (TRP) and purinergic P2X ion channels; yet the overall interaction of these mediators in neurogenic inflammation of cough pathways remains unclear.

OBJECTIVES

The World Allergy Organization/Allergic Rhinitis and its Impact on Asthma (WAO/ARIA) Joint Committee on Chronic Cough reviewed the current literature on neuroanatomy and pathophysiology of chronic cough. The role of TRP ion channels in pathogenic mechanisms of the hypersensitive cough reflex was also examined.

OUTCOMES

Chemoreceptors are better studied in cough neuronal pathways compared to stretch receptors, likely due to their anatomical overabundance in the respiratory tract, but also their distinctive functional properties. Central pathways are important in suppressive mechanisms and behavioral/affective aspects of chronic cough. Current evidence strongly suggests neurogenic inflammation induces a hypersensitive cough reflex marked by increased expression of neuromediators, mast cells, and eosinophils, among others. TRP ion channels, mainly TRP V1/A1, are important in the pathogenesis of chronic cough due to their role in mediating chemosensitivity to various endogenous and exogenous triggers, as well as a crosstalk between neurogenic and inflammatory pathways in cough-associated airways diseases.

Gender Difference in Chronic Cough: Are Women More Likely to Cough?

Chronic cough is a common complaint for patients to seek medical cares all over the world. Worldwide, about two thirds of chronic cough patients are females. However, in some regions of China the prevalence of chronic cough between sexes is roughly the same. Estrogen and progesterone can not only have an effect on transient receptor potential vanilloid 1 channel, eosinophils and mast cells, but also influence laryngeal dysfunction, gastroesophageal reflux disease and obstructive sleep apnea hypopnea syndrome, which may lead to increased cough sensitivity in women. On the other hand, the quality of life was adversely affected more in female patients with chronic cough. Both hormones possibly cause gender difference in chronic cough.

Prevalence and Characteristics of Chronic Cough in Adults Identified by Administrative Data

CONTEXT

International Classification of Diseases-9/10 codes for chronic cough (CC) do not exist, limiting investigation.

OBJECTIVE

To develop a computerized algorithm to determine CC prevalence and its characteristics.

DESIGN

This observational study using administrative data identified hierarchically patients aged 18 to 85 years with CC from 2013 to 2016. First, a specialist-diagnosed CC group was identified using an internal CC encounter code during an outpatient visit to a pulmonologist, allergist, otolaryngologist, or gastroenterologist. Subsequently, an event-diagnosed CC group was identified based on clinical notes through natural language processing, ICD-9/ICD-10 cough codes, and dispensed antitussives.

MAIN OUTCOME MEASURES

Prevalence of CC and comparison of clinical characteristics between specialist-diagnosed and event-diagnosed CC subgroups.

RESULTS

A total of 50,163 patients with CC of more than 8 weeks were identified. Of these, 11,290 (22.5%) were specialist diagnosed, and 38,873 (77.5%) were event diagnosed. The CC cohort was 57.4 ± 16.5 years of age; 67.6% were female. The overall prevalence was 1.04% (95% confidence interval = 1.03-1.06) in 2016. Prevalence in 2016 was higher in female patients (1.21%) than in male patients (0.81%), higher in patients aged 65 to 85 years (2.2%) than in patients aged 18 to 44 years (0.43%), and higher in Blacks (1.38%) than in Whites (1.21%). Compared with patients with event-diagnosed CC, patients with specialist-diagnosed CC exhibited significantly higher frequencies of laboratory tests and respiratory and nonrespiratory comorbidities and dispensed medication and lower frequency of pneumonia, all-cause and respiratory-cause emergency department visits and hospitalizations, and dispensed antitussives.

CONCLUSIONS

We identified a CC cohort using electronic data in a managed care organization. Prevalences varied by sex, age, and ethnicity. Clinical characteristics varied between specialist-diagnosed and event-diagnosed CC.

A Cold Environment Aggravates Cough Hyperreactivity in Guinea Pigs With Cough by Activating the TRPA1 Signaling Pathway in Skin

Cough exacerbation in cold environments is a characteristic feature of patients with chronic cough. There is consensus that inhalation of cold air stimulates cough receptors but this idea is not consistent with the fact that cold air is usually unable to directly enter the lower airway. To elucidate the effects of cold environments and transient receptor potential ankyrin 1 (TRPA1) on cough, we compared cough reactivity, airway inflammation, and TRPA1 expression in guinea pigs with chronic cough induced by the repeated inhalation of citric acid for 15 days. The guinea pigs were exposed to cold environments for three consecutive days from day 13 to 15. Repeated inhalation of citric acid increased cough reactivity to inhaled cinnamaldehyde. We found that exposure to cold environments further aggravated cough hyperreactivity in guinea pigs with chronic cough, but not in normal guinea pigs. Cough hyperreactivity was promoted when the whole body and trunk-limbs, but not the heads, of the guinea pigs were exposed to cold environments, and abolished by pretreating the skin through immersion in the TRPA1 antagonist, HC-030031. Substance P levels in bronchoalveolar lavage fluid, and TRPA1 expression in the trachea and skin, were increased in guinea pigs when the whole body and trunk-limbs, rather than the head, were exposed to cold environments. However, this trend was also abolished by pretreatment of the skin via immersion in HC-030031. Similar changes in TRPA1 expression were also detected in the sensory fibers of the trachea and skin, as identified by immunofluorescence and laser-scanning confocal microscopy analysis. These results suggest that exaggerated cough hyperreactivity induced by cold environments may be related to activation of the cold-sensing TRPA1 signaling pathway in the skin, rather than the inhalation of cold air.

A role for neurokinin 1 receptor expressing neurons in the paratrigeminal nucleus in bradykinin-evoked cough in guinea-pigs

KEY POINTS

Airway projecting sensory neurons arising from the jugular vagal ganglia terminate centrally in the brainstem paratrigeminal nucleus, synapsing upon neurons expressing the neurokinin 1 receptor. This study aimed to assess the involvement of paratrigeminal neurokinin 1 receptor neurons in the regulation of cough, breathing and airway defensive responses. Lesioning neurokinin 1 receptor expressing paratrigeminal neurons significantly reduced cough evoked by inhaled bradykinin but not inhaled ATP or tracheal mechanical stimulation. The reduction in bradykinin-evoked cough was not accompanied by changes in baseline or evoked respiratory variables (e.g. frequency, volume or timing), animal avoidance behaviours or the laryngeal apnoea reflex. These findings warrant further investigations into targeting the jugular ganglia and paratrigeminal nucleus as a therapy for treating cough in disease.

ABSTRACT

Jugular vagal ganglia sensory neurons innervate the large airways and are thought to mediate cough and associated perceptions of airway irritations to a range of chemical irritants. The central terminals of jugular sensory neurons lie within the brainstem paratrigeminal nucleus, where postsynaptic neurons can be differentiated based on the absence or presence of the neurokinin 1 (NK1) receptor. Therefore, in the present study, we set out to test the hypothesis that NK1 receptor expressing paratrigeminal neurons play a role in cough evoked by inhaled chemical irritants. To test this, we performed selective neurotoxin lesions of NK1 receptor expressing neurons in the paratrigeminal nucleus in guinea-pigs using substance P conjugated to saporin (SSP-SAP). Sham lesion control or SSP-SAP lesion guinea-pigs received nebulised challenges, with the pan-nociceptor stimulant bradykinin or the nodose ganglia specific stimulant adenosine 5'-triphosphate (ATP), in conscious whole-body plethysmography to study cough and associated behaviours. Laryngeal apnoea reflexes and cough evoked by mechanical stimulation of the trachea were additionally investigated in anaesthetised guinea-pigs. SSP-SAP significantly and selectively reduced the number of NK1 receptor expressing neurons in the paratrigeminal nucleus. This was associated with a significant reduction in bradykinin-evoked cough, but not ATP-evoked cough, mechanical cough or laryngeal apnoeic responses. These data provide further evidence for a role of jugular vagal pathways in cough, and additionally suggest an involvement of NK1 receptor expressing neurons in the paratrigeminal nucleus. Therefore, this neural pathway may provide novel therapeutic opportunities to treat conditions of chronic cough.

Prevalence and incidence of, and risk factors for chronic cough in the adult population: the Rotterdam Study

Chronic cough is a common complaint in the general population but there are no precise data on the incidence of, and prospectively examined risk factors for chronic cough in a population-based setting. Therefore, we investigated the period prevalence, incidence and risk factors for chronic cough in adult subjects. In a prospective population-based cohort study among subjects aged ≥45 years, data on chronic cough were collected on two separate occasions using a standardised questionnaire. Chronic cough was defined as daily coughing for at least 3 months duration during the preceding 2 years. Potential risk factors were gathered by interview, physical examination and several investigations. Of the 9824 participants in this study, 1073 (10.9%) subjects had chronic cough at baseline. The prevalence of chronic cough increased with age and peaked in the eighth decade. In subjects aged <70 years, chronic cough was more common in women. During an average follow-up of 6 years, 439 incident cases of chronic cough occurred with an overall incidence rate of 11.6 per 1000 person-years (95% CI 10.6-12.8). In current smokers, the incidence of chronic cough was higher in men. In the multivariable analysis, current smoking, gastro-oesophageal reflux disease (GORD), asthma and COPD were identified as risk factors for chronic cough. Chronic cough is common among adults and highly prevalent in the older population. Current smoking, GORD, asthma and COPD are independent risk factors for chronic cough. Individuals at risk of developing chronic cough may benefit from smoking cessation and control of the underlying disease.

Female Guinea Pig Model for Cough Studies and Its Response to Most Common Tussive Substances

Laboratory research of cough reflex utilizes almost exclusively male guinea pigs – a practice that represents a significant obstacle in the successful translation of results into clinical practice. Chronic hypersensitivity cough syndrome affects mostly postmenopausal women and it represents significant decrease in patient’s quality of life. No cause for such exaggerated cough can be found, therefore this condition cannot be treated appropriately. One of the reasons leading to the lack of relevant data about mechanisms responsible for hypersensitivity of cough related pathways is nowadays widely discussed gender bias, which is present in nearly all branches of biomedical research. Since gender differences in cough reflex physiology do exist in humans, it would be reasonable to study cough-related phenomena on both sexes of laboratory animals. In this study, we focused on detailed characterization of cough response of female guinea pigs to aerosols of commonly used tussive agents (capsaicin, distilled water, allyl isothiocyanate, cinnamaldehyde, citric acid). In pooled data from multiple challenges we found no statistical difference in number of cough and cough latency between sexes. Based on our results we conclude that the utilization of female guinea pigs model does not lead to messy data and can be used in basic cough research.

Burden of Specialist-Diagnosed Chronic Cough in Adults

BACKGROUND

The burden of chronic cough (CC) in patients seeking specialist care is infrequently researched.

OBJECTIVE

To describe patient characteristics and disease burden associated with specialist-diagnosed CC.

METHODS

Using administrative pharmacy and medical data, we identified patients aged 18 to 85 years with CC diagnosed by pulmonologists, allergists, otolaryngologists, or gastroenterologists. Patients were stratified into 4 subgroups on the basis of the presence or absence of common respiratory diseases or gastroesophageal reflux disease (GERD). Clinical features and health care resource utilization (HCRU) in the baseline and outcome years were compared between the CC subgroups. The baseline factors associated with persistence of CC and a comparison of the CC cohort to a matched noncough cohort were also determined.

RESULTS

The 11,290 patients with specialist-diagnosed CC were aged about 61 years and 66.7% were females. The CC cohort experienced frequent GERD (44.1%), asthma (31.2%), obesity (24.3%), upper airway cough syndrome (20.4%), common cough complications (19.4%), and hospitalizations (9.8%). The patients with CC with both respiratory disease and GERD exhibited at baseline and follow-up the most common cough comorbidities, higher HCRU, specialist care, and dispensed respiratory and nonrespiratory medications including proton pump inhibitors, antitussives, psychotherapeutics, oral corticosteroids, and antibiotics compared with the other subgroups. A 40.6% persistence of CC occurred similarly between CC subgroups. In addition, patients with CC in the matched analysis experienced significantly more comorbidities, laboratory evaluations, HCRU, and antitussives than patients without cough.

CONCLUSIONS

Specialist-diagnosed CC was associated with considerable disease burden, particularly among those with both respiratory disease and GERD. In addition, CC burden was more pronounced than in matched patients without cough.

Immune system in the pathogenesis of chronic cough

Chronic cough is a common symptom of various chronic diseases. However, the vast majority of individuals with conditions that are commonly associated with cough, such as asthma and GERD, do not have chronic cough. This implies that cough reflex sensitivities differ among individuals. It is known that in the pathogenesis of cough, the nervous system plays a vital role. Recently more information about the role of the immune system and its interaction with the nervous system in the pathogenesis of cough has appeared in the literature. The aim of this article is to review the most recent data about the role of the immune system in the pathogenesis of chronic cough.

Comparison of mannitol and citric acid cough provocation tests

RATIONALE

Citric acid has been used as a cough provocation test for decades. However, the methods of administration have not been standardized. Inhaled mannitol is a novel cough provocation test, which has regulatory approval and can be performed utilizing a simple disposable inhaler in a standardized manner.

OBJECTIVE

To compare the mannitol and citric acid cough provocation tests with respect to their ability to identify subjects with chronic cough and their tolerability.

METHODS

Subjects with chronic cough (n = 36) and controls (n = 25) performed provocation tests with mannitol and citric acid. Both tests were video recorded. Cough sensitivity was expressed as coughs-to-dose ratios (CDR) and the cumulative doses to mannitol or concentration to citric acid evoking 5 coughs (C5). Forced expiratory volume in 1 s (FEV₁), visual analogue scales (VAS), test completion rates and the total cough frequencies were analysed.

RESULTS

Mannitol and citric acid CDR both effectively separated those with cough and the control subjects (AUC 0.847 and 0.803, respectively) as did C5 (AUC 0.823 and 0.763, respectively). There was a good correlation between the cough sensitivity provoked by the two stimuli, either expressed as CDR (r = 0.65, p < 0.001) or C5 (r = 0.53, p = 0.001). Both tests were similarly tolerated in terms of VAS, although more patients discontinued the mannitol test early, primarily due to cough.

CONCLUSIONS

Mannitol and citric acid tests correlated well, equally identified subjects with chronic cough and their tolerability was similar. The feasibility issues, strict standardisation and regulatory approval may favour mannitol to be used in clinical cough research.

The management of chronic cough

Chronic cough is a common presentation to primary care and constitutes a significant volume of referrals to secondary care. It affects around 10% of the adult population and has a plethora of respiratory and non-respiratory causes. It can have a significant impact on the quality of life of affected individuals. In many patients, minimal baseline investigations lead to an easily identifiable and treatable cause. In others, no cause can be identified even after extensive investigations in specialized cough clinics. This evidence-based review article outlines the approach to the adult patient presenting with chronic cough and focuses upon current management strategies in those with chronic idiopathic cough. It includes results from trials of speech and language therapies, and the emerging concept of chronic idiopathic cough as a neuropathic disorder with its own bespoke approach to management including the use of neuromodulatory agents.

Vagal Afferent Processing by the Paratrigeminal Nucleus

The paratrigeminal nucleus is an obscure region in the dorsal lateral medulla, which has been best characterized as a collection of interstitial cells located in the dorsal tip of the spinal trigeminal tract. The paratrigeminal nucleus receives afferent input from the vagus, trigeminal, spinal, and glossopharyngeal nerves, which contribute to its long-known roles in the baroreceptor reflex and nociceptive processing. More recently, studies have shown that this region is also involved in the processing of airway-derived sensory information. Notably, these studies highlight an underappreciated complexity in the neuronal content and circuit connectivity of the paratrigeminal nucleus. However, much remains to be understood about how paratrigeminal processing of vagal afferents is altered in disease. The aim of the present review is to provide an update of the current understanding of vagal afferent processing in the paratrigeminal nucleus and to explore how dysregulation at this site may contribute to vagal sensory neural dysfunction during disease.

Predictors of prolongation in recent-onset cough

Chronic cough greatly decreases the quality of life and is often refractory to treatment. Interventions at an early stage could prevent cough from becoming chronic. To this end, the patients at high risk of cough prolongation would need to be identified. In this study, we investigated the factors that predicted cough at 12 months among subjects with a recent-onset cough. This was a prospective, observational follow-up study in a community-based population consisting of working-age subjects. The first e-mail survey in 2017 included a comprehensive questionnaire about current cough and its risk factors. The 259 subjects who reported a recent-onset (<8 weeks) cough were sent a follow-up questionnaire 12 months later. The response rate was 72.6% (188 subjects). There were 99 subjects (52.7%) with cough in 2018. The following baseline factors predicted the presence of any cough at 12 months in the multivariable analysis: wheezing (adjusted odds ratio (aOR 2.80, 95% CI 1.3-5.27), dog ownership (aOR 2.56, 95% CI 1.21-5.44), cough duration >3 weeks (aOR 2.29, 95% CI 1.11-4.76), family history of chronic cough (aOR 2.20, 95% CI 1.13-4.30), body mass index >25 kg·m-2 (aOR 2.06, 95% CI 1.02-4.15) and frequent somatic symptoms (aOR 1.36, 95% CI 1.13--1.64). There were 29 subjects (15.4%) with continuous cough and 66 subjects (35.1%) with recurrent cough. The risk factors were completely different between recurrent and continuous cough. It may be possible to identify the risk factors of cough prolongation among subjects with recent-onset cough. Early interventions should be targeted to these kinds of patients.

Assessing referral and practice patterns of patients with chronic cough referred for behavioral cough suppression therapy

The purpose of this exploratory research was to describe current referral and practice patterns for behavioral cough suppression therapy (BCST) throughout the United States, and to assess the need for improving the efficiency of BCST referral patterns. In study I, 126 speech-language pathologists, who treat patients with refractory chronic cough (RCC) in the United States, completed a survey about referral patterns, cough duration, and patient frustration level. In study II, 36 adults with RCC referred for BCST completed a four-part survey about cough symptoms and treatment. The survey included the Leicester Cough Questionnaire (LCQ) before and after BCST. Study I revealed significant patient frustration about the treatment process and the wait-time for BCST. Participants in study II reported average cough duration of over 2 years before BCST. Twenty-seven of 31 participants in study II improved by at least 1.3 on the LCQ, indicating a clinically significant improvement in 87% of patients. This study suggests that the current management model for CC may be unduly time-consuming, and expensive for patients with CC who are successfully treated with BCST. Practitioners are encouraged to consider BCST earlier in the treatment process.

Managing patients with chronic cough: challenges and solutions

Chronic cough is a common complaint and a frequent cause of medical consultation. Its management can be difficult. We present here an overview of the current guidelines for the management of chronic cough. Different steps are detailed, including the initial research of an obvious etiology and alert signs that should lead to further investigation of underlying condition. The diagnosis of the most frequent causes: asthma, non-asthmatic eosinophilic bronchitis, gastroesophageal reflux disease and upper airway cough syndrome should be considered, assessed and treated accordingly. Recent advances have been made in the comprehension of refractory chronic cough pathophysiology as well as its pharmacologic and non-pharmacologic treatment, especially speech pathology therapy.

Chalk-induced Lung Fibrosis — Case Report

Introduction: Our article underlines the importance of a good professional anamnesis, knowing all the chemical components with which the patient had been exposed to during her active life as a teacher.

Case presentation: A 64-year-old female patient, teacher for 27 years, who had been retired for six years, presented cough with white phlegm and shortness of breath occurring during physical exertion, diffuse thoracic pain, and fatigue. Several lung functional tests were performed, which established the diagnosis of irreversible minor mixed ventilatory dysfunction. In order to establish the etiology of the patient’s symptoms, multiple clinical, laboratory, imaging, and functional investigations were performed including a chest radiograph, pulmonary functional testing, bronchial reversibility testing, a thoracic CT scan, fibrobronchoscopy, alveolar-capillary diffusion capacity measurement, otorhinolaryngology examination, thyroid ultrasound, as well as a cardiological consult. Finally, a positive diagnosis was established: bronchial hyperreactivity syndrome, chalk dust-induced diffuse pulmonary fibrosis.

Conclusion: An essential part of clinical practice is a proper anamnesis, including detailed information on the professional history and exposure, as well as the composition of the dust/particles with which the patient had been in contact with.

Inhibitors of phosphodiesterases in the treatment of cough

A group of 11 enzyme families of metalophosphohydrolases called phosphodiesterases (PDEs) is responsible for a hydrolysis of intracellular cAMP and cGMP. Xanthine derivatives (methylxanthines) inhibit PDEs without selective action on their single isoforms and lead to many pharmacological effects, e.g. bronchodilation, anti-inflammatory and immunomodulating effects, and thus they can modulate the cough reflex. Contrary, selective PDE inhibitors have been developed to inhibit PDE isoforms with different pharmacological effects based on their tissue expression. In this paper, effects of non-selective PDE inhibitors (e.g. theophylline) are discussed, with a description of other putative mechanisms in their effects on cough. Antitussive effects of selective inhibitors of several PDE isoforms are reviewed, focusing on PDE1, PDE3, PDE4, PDE5 and PDE7. The inhibition of PDEs suggests participation of bronchodilation, suppression of TRPV channels and anti-inflammatory action in cough suppression. Selective PDE3, PDE4 and PDE5 inhibitors have demonstrated the most significant cough suppressive effects, confirming their benefits in chronic inflammatory airway diseases associated with bronchoconstriction and cough.

Sensitivity of airway cough-related afferents is influenced by female sex hormones

Chronic hypersensitivity cough syndrome affects mainly postmenopausal women; however, the pathogenesis of cough hypersensitivity in this demographic is not entirely understood. The role of sex hormones in cough has never been studied in detail; however, sex hormones seem to play an important role in the lung health of women. Our study was aimed to analyse the effect of female sex hormones (oestrogen - E2 and progesterone - Pg) on cough sensitivity measured by inhalation of capsaicin in follicular and luteal phases of menstrual cycle, characterized by significantly different concentrations of sex hormones. These data were compared with a matched group of women taking oral contraceptives. Cough sensitivity to capsaicin increased in luteal phase in subjects with normal menstrual cycle, and this functional change was not present in group with contraceptive pills. The cough sensitivity correlates with the Pg/E2 ratio, and relative lack of oestrogen in luteal phase is associated with higher cough sensitivity to capsaicin.

Role of gender in basic cough research

Cough hypersensitivity affects mainly postmenopausal women. Pathogenesis remains unknown in their case; therefore, an optimal treatment is unavailable. Only male guinea pigs are used in basic cough research and exclusion of females leads to gender bias. Nowadays, the efforts of grant agencies aim to support projects which take gender into account and involve both sexes to reduce gender bias. The aim of our pilot study is to assess the suitability of female guinea pig model in cough research. Cough response to citric acid (0.4M) was obtained in female and male guinea pigs (n=12 each). Reproducibility of cough response was tested four times a week apart. The cough was detected from the airflow traces and cough sound analysis. Our initial results show that cough response of female guinea pigs is higher than in males. Variability of females is also higher than in males. Further investigations are necessary to validate this model in different conditions to achieve gender equality in cough studies.

Patient considerations and drug selection in the treatment of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease of unknown cause. Approximately 5,000 people are diagnosed with IPF in the UK every year. People with IPF suffer significant morbidity and, without any curative treatment at present, survival rates remain poor with a median survival of 3 years. While treatment remains largely supportive, many drug therapies have been trialed in IPF over the years. Pirfenidone and nintedanib are newly licensed treatments for IPF and the first drugs to have shown convincing evidence of slowing disease progression. In addition to evaluating clinical evidence, we also discuss elements affecting drug choice from the viewpoint of patients and health care professionals. We discuss pharmacological and nonpharmacological aspects of providing best supportive care for patients with IPF. However, few good quality studies exist focusing on controlling symptoms specifically in patients with IPF, and recommendations are often extrapolated from evidence in other chronic diseases. In covering these topics, we hope to provide readers with a comprehensive review of the available evidence pertaining to all aspects of care for patients suffering with IPF.

Efficacy and safety of Maekmoondong-tang for chronic dry cough: a study protocol for a randomized controlled trial

Background

Chronic cough, defined it lasts more than 8 weeks. The symptom is common, but highly troublesome, and it reduces quality of life. Despite much effort to develop a protocol for diagnosis and treatment of chronic cough, it remains problematic to determine its cause. As a result, treatment is often unsuccessful. Thus, there is much interest regarding the use of symptomatic drugs to control chronic cough.

Maekmoondong-tang is widely used in East Asian countries to treat chronic dry cough. Several experimental studies have reported that the herbal medicine has immunomodulatory and antitussive effects. Clinical studies involving Maekmoondong-tang have also been carried out; however, these studies have involved treating various diseases as a whole rather than chronic cough itself. Thus, we aim to evaluate the efficacy and safety of Maekmoondong-tang in chronic dry cough patients with a randomized controlled trial.

Methods/Design

This study is designed as an exploratory, single-center, placebo-controlled, double-blind, randomized, parallel group clinical trial. Patients with dry cough that has lasted more than 8 weeks will be recruited, after a 1-week run-in period, and randomly allocated to either the Maekmoondong-tang treatment group or the placebo group. The patients will receive Maekmoondong-tang or placebo granules 3 times daily for 4 weeks, with a 2-week follow-up. The primary outcome is a 10-point cough diary that will be recorded on a daily basis. The secondary outcomes comprise a cough visual analog scale, the Leicester Cough Questionnaire (Korean version), the Pattern Identification for Chronic Cough Questionnaire, biomarkers, safety testing, etc. Adverse events will also be reported.

Discussion

This trial will assess the efficacy and safety of Maekmoondong-tang in chronic dry cough.

Trial registration

Korean Clinical Trial Registry (http://cris.nih.go.kr; registration number: KCT0001646). Date of registration: October 5 2015

Capsaicin cough sensitivity and the association with clinical parameters in bronchiectasis

BACKGROUND

Cough hypersensitivity has been common among respiratory diseases.

OBJECTIVE

To determine associations of capsaicin cough sensitivity and clinical parameters in adults with clinically stable bronchiectasis.

METHODS

We recruited 135 consecutive adult bronchiectasis patients and 22 healthy subjects. History inquiry, sputum culture, spirometry, chest high-resolution computed tomography (HRCT), Leicester Cough Questionnaire scoring, Bronchiectasis Severity Index (BSI) assessment and capsaicin inhalation challenge were performed. Cough sensitivity was measured as the capsaicin concentration eliciting at least 2 (C2) and 5 coughs (C5).

RESULTS

Despite significant overlap between healthy subjects and bronchiectasis patients, both C2 and C5 were significantly lower in the latter group (all P<0.01). Lower levels of C5 were associated with a longer duration of bronchiectasis symptoms, worse HRCT score, higher 24-hour sputum volume, BSI and sputum purulence score, and sputum culture positive for P. aeruginosa. Determinants associated with increased capsaicin cough sensitivity, defined as C5 being 62.5 µmol/L or less, encompassed female gender (OR: 3.25, 95%CI: 1.35-7.83, P<0.01), HRCT total score between 7-12 (OR: 2.57, 95%CI: 1.07-6.173, P = 0.04), BSI between 5-8 (OR: 4.05, 95%CI: 1.48-11.06, P<0.01) and 9 or greater (OR: 4.38, 95%CI: 1.48-12.93, P<0.01).

CONCLUSION

Capsaicin cough sensitivity is heightened in a subgroup of bronchiectasis patients and associated with the disease severity. Gender and disease severity, but not sputum purulence, are independent determinants of heightened capsaicin cough sensitivity. Current testing for cough sensitivity diagnosis may be limited because of overlap with healthy subjects but might provide an objective index for assessment of cough in future clinical trials.

Attentional modulation of reflex cough

OBJECTIVE

Reflex cough is a defensive response generated in the brainstem in response to chemical and mechanical stimulation of the airways. However, converging evidence shows that reflex cough is also influenced by central neural control processes. In this study, we investigate whether reflex cough can be modulated by attentional focus on either external stimuli or internal cough-related stimuli.

METHODS

Healthy volunteers (N = 24; seven men; age range, 18-25 years) completed four blocks of citric acid-induced cough challenges while, simultaneously, auditory stimuli were presented. Within each block, four concentrations were administered (30, 100, 300 and 1,000 mM, randomized). During two subsequent blocks, participants focused their attention externally (counting tones). During the other two blocks, participants focused their attention internally (counting coughs). The order of attentional focus was counterbalanced across participants. Ratings of the urge to cough were collected after each challenge. Cough frequency was determined by audio recording.

RESULTS

Cough frequency was higher when participants focused their attention internally vs externally (P < .05). Also urge to cough was greater during internal vs external focus (P < .05), but the effect was smaller in later blocks of trials.

CONCLUSIONS

Reflex cough can be modulated by attentional focus. Internally focused attention may be a mechanism involved in excessive (idiopathic) cough, while an external focus may be introduced as part of treatments targeting excessive cough.

What is chronic cough in children?

The cough reflex is modulated throughout growth and development. Cough—but not expiration reflex—appears to be absent at birth, but increases with maturation. Thus, acute cough is the most frequent respiratory symptom during the first few years of life. Later on, the pubertal development seems to play a significant role in changing of the cough threshold during childhood and adolescence resulting in sex-related differences in cough reflex sensitivity in adulthood. Asthma is the major cause of chronic cough in children. Prolonged acute cough is usually related to the long-lasting effects of a previous viral airway infection or to the particular entity called protracted bacterial bronchitis. Cough pointers and type may orient toward specific etiologies, such as barking cough in croup or tracheomalacia, paroxystic whooping cough in Pertussis. Cough is productive in protracted bacterial bronchitis, sinusitis or bronchiectasis. Cough is usually associated with wheeze or dyspnea on exertion in asthma; however, it may be the sole symptom in cough variant asthma. Thus, pediatric cough has particularities differentiating it from adult cough, so the approach and management should be developmentally specific.

Chronic cough: an otorhinolaryngology perspective

PURPOSE OF REVIEW

Cough lasting more than 8 weeks is a common presenting complaint to the otolaryngologist. Historically, chronic cough has been attributed to post-nasal drip, laryngopharyngeal reflux and cough-variant asthma. This study reviews chronic cough from the viewpoint of an otolaryngologist.

RECENT FINDINGS

More recent studies suggest the influence of laryngeal neuropathy and its interplay with laryngopharyngeal reflux. There is limited evidence for post-nasal drip or cough-variant asthma causing chronic cough.

SUMMARY

In this study, we review the evidence for cause of chronic cough, as well as up to date techniques for the otolaryngologist, including transnasal esophagoscopy, to assess the patient in clinic allowing accurate diagnosis. Treatment options for the otolaryngologist are discussed and the role of multidisciplinary input emphasized.

On the definition of chronic cough and current treatment pathways: an international qualitative study

BACKGROUND

The pathogenesis of chronic cough is not well understood and treatment options are limited. In this study we sought to explore the current understanding and management of chronic cough across an international group of specialists.

METHODS

This was an international study of cross sectional qualitative design. In depth interviews were carried out with "Respiratory Specialists" experienced in treating treating Chronic Obstructive Pulmonary Disease (COPD), idiopathic pulmonary fibrosis (IPF), idiopathic chronic cough (ICC) and/or lung cancer patients and with "Disease Experts" in the field of Chronic Cough. Participants in the study were recruited from the USA, UK, Germany, Ireland, Australia and Japan. Interviews with specialists were held at research facilities and with DEs over the telephone. These were preceded by the specialists completing case records of patients recently seen. All interviews were conducted by native speaking trained moderators using a semi-structured interview guide script. This was designed to elicit the definition of chronic cough, explore the unmet needs for each disease state, define therapy goals, identify patient phenotypes and give an overview of the treatment pathway.

RESULTS

76 specialists and 10 experts took part in the study. Over two thirds (70%) of respondents defined chronic cough as "cough lasting more than 8/12 weeks" (range 2 weeks to 2 years). Physicians emphasised three interdependent aspects of clinical assessment: impact on quality of life, type of cough (productive versus non-productive) and the underlying pathology. Specialists emphasised treating the underlying cause rather than the cough, this being most prominent in Japan. Experts as a group focussed on chronic cough independently. Evaluation of the respiratory system, GI tract and upper airway (ENT) for establishing an underlying cause was recommended. Type of cough (productive vs non-productive) and impact on quality of life influenced treatment initiation. 33% of patients with ICC were prescribed anti-tussives. With associated diagnoses of COPD, IPF or lung cancer the emphasis was on treating the underlying condition. Alternatives to pharmacological treatments were frequently considered.

CONCLUSION

There is significant international variation in our understanding and management of chronic cough. Further work is required to bring forth clear guidance and effective medicines for these patients.

Capsaicin cough sensitivity is related to the older female predominant feature in chronic cough patients

Purpose

The present study aimed to examine the age and gender distributions among chronic cough patients referred to a tertiary cough clinic in Korea, and to investigate clinical factors related to the demographic findings.

Methods

Study participants were unselectively recruited from adult chronic cough patients who attended the cough clinic for the first time during one year. To validate their representativeness, their age and gender distributions were compared to the entire chronic cough population, or with those presenting with other chronic disease. Data from the baseline investigations were analyzed to identify clinical factors related to the demographic findings.

Results

A total of 272 chronic cough patients were included. They had a middle-aged female predominant feature (mean age: 52.8±15.7 years and female 69.1%). Their age and gender distributions were almost identical to the entire chronic cough population, but were distinct from patients with hypertension. Among clinical factors, the older female predominance was associated with enhanced capsaicin cough sensitivity, and also with the presence of 'cough by cold air' symptom. Allotussia and laryngeal paresthesia were highly common in chronic cough patients, affecting 94.8% and 86.8% of them, respectively.

Conclusions

The present study demonstrated older female predominance among adult chronic cough patients attending a referral cough clinic in Korea. The demographic features were significantly associated with the capsaicin cough responses and also potentially with allotussia (particularly cold air as the trigger). These findings suggest a role of cough reflex sensitization in the pathophysiology of chronic cough in adults.