Chronic cough: from a complex dysfunction of the neurological circuit to the production of persistent cough

Practical multidisciplinary framework for the assessment and management of patients with unexplained chronic aerodigestive symptoms

OBJECTIVE

Patients experiencing unexplained chronic throat symptoms (UCTS) are frequently referred to gastroenterology and otolaryngology outpatient departments for investigation. Often despite extensive investigations, an identifiable structural abnormality to account for the symptoms is not found. The objective of this article is to provide a concise appraisal of the evidence-base for current approaches to the assessment and management of UCTS, their clinical outcomes, and related healthcare utilisation.

DESIGN

This multidisciplinary review critically examines the current understanding of aetiological theories and pathophysiological drivers in UCTS and summarises the evidence base underpinning various diagnostic and management approaches.

RESULTS

The evidence gathered from the review suggests that single-specialty approaches to UCTS inadequately capture the substantial heterogeneity and pervasive overlaps among clinical features and biopsychosocial factors and suggests a more unified approach is needed.

CONCLUSION

Drawing on contemporary insights from the gastrointestinal literature for disorders of gut-brain interaction, this article proposes a refreshed interdisciplinary approach characterised by a positive diagnosis framework and patient-centred therapeutic model. The overarching aim of this approach is to improve patient outcomes and foster collaborative research efforts.

Atypical Activation of Laryngeal Somatosensory-Motor Cortex During Vocalization in People With Unexplained Chronic Cough

Importance

Unexplained chronic cough is common and has substantial negative quality-of-life implications, yet its causes are not well understood. A better understanding of how peripheral and central neural processes contribute to chronic cough is essential for treatment design.

Objective

To determine if people with chronic cough exhibit signs of abnormal neural processing over laryngeal sensorimotor cortex during voluntary laryngeal motor activity such as vocalization.

Design, Setting, and Participants

This was a cross-sectional study of a convenience sample of participants with chronic cough and healthy participants. Testing was performed in an acoustically and electromagnetically shielded chamber. In a single visit, electroencephalographic (EEG) signals were recorded from participants with chronic cough and healthy participants during voice production. The chronic cough group participants presented with unexplained cough of 8 weeks or longer duration with prior medical evaluation including negative results of chest imaging. None of the participants had a history of any neurologic disease known to impair vocalization or swallowing. Data collection for the healthy control group occurred from February 2 to June 28, 2018, and for the chronic cough group, from November 22, 2021, to June 21, 2022. Data analysis was performed from May 1 to October 30, 2022.

Exposure

Participants with or without chronic cough.

Main Outcome Measures

Event-related spectral perturbation over the laryngeal area of somatosensory-motor cortex from 0 to 30 Hz (ie, θ, α, and β bands) and event-related coherence as a measure of synchronous activity between somatosensory and motor cortical regions.

Results

The chronic cough group comprised 13 participants with chronic cough (mean [SD] age, 63.5 [7.8] years; 9 women and 4 men) and the control group, 10 healthy age-matched individuals (mean [SD] age, 60.3 [13.9] years; 6 women and 4 men). In the chronic cough group, the typical movement-related desynchronization over somatosensory-motor cortex during vocalization was significantly reduced across θ, α, and β frequency bands when compared with the control group.

Conclusions and Relevance

This cross-sectional study found that the typical movement-related suppression of brain oscillatory activity during vocalization is weak or absent in people with chronic cough. Thus, chronic cough affects sensorimotor cortical activity during the asymptomatic voluntary activation of laryngeal muscles.

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.

Chronic cough exerts a considerable burden on patients and healthcare systems. In addition to effective targeted therapies, further data are needed to understand the pathophysiology, epidemiology and disease burden.https://bit.ly/3Be9JZI

Prostaglandin E2 sensitizes the cough reflex centrally via EP3 receptor-dependent activation of NaV 1.8 channels

Background

Cough hypersensitivity is a major characteristic feature associated with several types of cough, including chronic cough, but its underlying mechanisms remain to be fully understood. Inflammatory mediators, such as prostaglandin E₂ (PGE₂), have been implicated in both peripheral induction and sensitization of the cough reflex. In this study, using a conscious guinea pig model of cough, we investigated whether PGE₂ can sensitize the cough reflex via central actions and, if so, via which mechanisms.

Methods

All drugs were administered by intracerebroventricular (i.c.v.) route and whole-body plethysmograph set-up was used for both induction, using aerosolized citric acid (0.2 M), and recording of cough. Immunohistochemistry was performed to confirm the expression of NaV 1.8 channels in the nucleus tractus solitarius (nTS).

Results

We show that both PGE₂ and the non-selective EP1/EP3 agonist, sulprostone, dose-dependently enhanced the citric acid-induced cough (P ≤ 0.001, P ≤ 0.01, respectively). Pretreatment with the EP1 antagonist, ONO-8130, did not affect the sulprostone-induced cough sensitization, whilst the EP3 antagonist, L-798,106, dose-dependently inhibited this effect (P ≤ 0.05). Furthermore, treatment with either the EP2 agonist, butaprost or the EP4 agonist, L-902,688, had no effect on cough sensitization. Additionally, pretreatment with either the TRPV1 antagonist, JNJ-17203212 or the TRPA1 antagonist, HC-030031, alone or in combination, nor with the NaV 1.1, 1.2, 1.3, 1.4, 1.6 and 1.7 channel blocker, tetrodotoxin, had any effect on the cough. In contrast, pretreatment with the NaV 1.8 antagonist, A-803467, dose-dependently inhibited this effect (P ≤ 0.05). Furthermore, NaV 1.8 channels were shown to be expressed in the nTS.

Conclusion

Collectively, our findings show that PGE₂ sensitizes the cough reflex centrally via EP3 receptor-dependent activation of NaV 1.8 but independently of TRPV1,TRPA1 and TTX-sensitive sodium channel activation. These results indicate that PGE₂ plays an important role in central sensitization of the cough reflex and suggest that central EP3 receptors and/or NaVv 1.8 channels may represent novel antitussive molecular targets.

Graphical Abstract

The interrelatedness of chronic cough and chronic pain

Since chronic cough has common neurobiological mechanisms and pathophysiology with chronic pain, both clinical disorders might be interrelated. Hence, we examined the association between chronic cough and chronic pain in adult subjects in the Rotterdam Study, a large prospective population-based cohort study.Using a standardised questionnaire, chronic pain was defined as pain lasting up to 6 months and grouped into a frequency of weekly/monthly or daily pain. Chronic cough was described as daily coughing for at least 3 months duration. The longitudinal and cross-sectional associations were investigated bi-directionally.Of 7141 subjects in the study, 54% (n=3888) reported chronic pain at baseline. The co-prevalence of daily chronic pain and chronic cough was 4.4%. Chronic cough was more prevalent in subjects with daily and weekly/monthly chronic pain compared with those without chronic pain (13.8% and 10.3% versus 8.2%; p<0.001). After adjustment for potential confounders, prevalent chronic pain was significantly associated with incident chronic cough (OR 1.47, 95% CI 1.08-1.99). The association remained significant in subjects with daily chronic pain (OR 1.49, 95% CI 1.06-2.11) with a similar effect estimate, albeit non-significant in those with weekly/monthly chronic pain (OR 1.43, 95% CI 0.98-2.10). After adjustment for covariables, subjects with chronic cough had a significant risk of developing chronic pain (OR 1.63, 95% CI 1.02-2.62) compared with those without chronic cough.Chronic cough and chronic pain confer risk on each other among adult subjects, indicating that both conditions might share common risk factors and/or pathophysiologic mechanisms.

The Role of Transient Receptor Potential Vanilloid 1 in Common Diseases of the Digestive Tract and the Cardiovascular and Respiratory System

Transient receptor potential vanilloid subtype 1 (TRPV1), a member of the transient receptor potential vanilloid (TRPV) channel family, is a nonselective cation channel that is widely expressed in sensory nerve fibers and nonneuronal cells, including certain vascular endothelial cells and smooth muscle cells. The activation of TRPV1 may be involved in the regulation of various physiological functions, such as the release of inflammatory mediators in the body, gastrointestinal motility function, and temperature regulation. In recent years, a large number of studies have revealed that TRPV1 plays an important role in the physiological and pathological conditions of the digestive system, cardiovascular system, and respiratory system, but there is no systematic report on TRPV1. The objective of this review is to explain the function and effects of TRPV1 on specific diseases, such as irritable bowel syndrome, hypertension, and asthma, and to further investigate the intrinsic relationship between the expression and function of TRPV1 in those diseases to find new therapeutic targets for the cure of related diseases.

Effect of pregabalin for the treatment of chronic refractory cough: A case report

RATIONALE

Chronic refractory cough (CRC) is a common clinical problem which is more likely associated with some physical problems. Although many patients have received satisfactory treatment, there were still many patients suffered from long-term cough symptoms after standardized treatment.

PATIENT CONCERNS

A patient suffered from postherpetic neuralgia (PHN) and also he complained CRC for more than 20 years.

DIAGNOSIS

The patient was diagnosed with PHN and CRC.

INTERVENTIONS

Pregabalin was originally administered to treat PHN.

OUTCOMES

pregabalin not only alleviated her pain of PHN but also relieved chronic cough.

LESSONS

This report demonstrated the surprising effect of pregabalin on the treatment of CRC.

Chronic Cough in Adults: Make the Diagnosis and Make a Difference

Chronic cough is common and impactful, frustrating both patients and clinicians. An empirical trial of therapy is often done with inhaled corticosteroids, but this practice should be replaced with attempting to make an accurate diagnosis. The three most common causes are upper airway cough syndrome, asthma, and gastroesophageal reflux disease (GERD), but there are often multiple causes involved. Minimal investigations after history, physical exam, travel history, and drug history include a chest radiograph and spirometry. Empirical trial of therapy with inhaled corticosteroids is reasonable if there is evidence of eosinophilic inflammation. Empiric therapy for GERD may also be reasonable in those with symptoms. Red flags should especially be considered an urgency to make the correct diagnosis.

Tachyphylaxis and Dependence in Pharmacotherapy for Unexplained Chronic Cough

Objective Unexplained chronic cough (UCC) is a perplexing condition treated with neuromodulators. Although previous literature describes the effectiveness of neuromodulators, there is little on the development of tachyphylaxis or dependence to neuromodulators over time. Our objective is to capture the experience of a large cohort of patients with UCC over an extended period, looking for these 2 phenomena. Study Design Case series with chart review. Setting Tertiary care hospital. Subjects and Methods We performed a retrospective review of patients diagnosed with UCC from 2010 to 2014. Patient outcomes were measured through percentage improvement scores. Treatment failures were attributed to no benefit, intolerable side effects, or tachyphylaxis. Tachyphylaxis was defined as the need for higher doses of medication following diminishing therapeutic benefit, while dependence was defined as a failure to stop therapy following attempted de-escalation or resurgence following drug cessation. Results Sixty-eight patients were included in the study. Tachyphylaxis was observed among 35% of patients while dependence was observed among 27% of successfully treated patients, together effecting >50% of the cohort. Sixty-eight percent of patients ultimately experienced successful treatment with neuromodulators, demonstrating strikingly distinct responses to different neuromodulator drug classes. Conclusion Tachyphylaxis and dependence occur frequently during UCC treatment and have a major impact on treatment outcomes. Patients sometimes demonstrate distinct responses to different neuromodulator classes. The majority of patients will experience successful treatment for their cough, although several trials may be required.

Short- and Long-term Effects of Neuromodulators for Unexplained Chronic Cough

Objective

To evaluate the short- and long-term effects of tricyclic antidepressants (TCAs) and gabapentin in the treatment of unexplained chronic cough (UCC).

Study Design

Prospective cohort.

Setting

Tertiary care hospital.

Subjects and Methods

Patients seen between July 2016 and March 2017 were included following a formal workup and clinical evaluation indicative of UCC. Patients were placed on either a TCA (amitriptyline or nortriptyline) or gabapentin. Leicester Cough Questionnaire (LCQ) and percentage improvement scores were obtained prior to treatment initiation and at 2 and 6 months of neuromodulator treatment. A linear mixed model assessed the change in LCQ score between the 2 treatment time points and baseline scores.

Results

Twenty-eight patients completed a total of 37 neuromodulator trials. Gabapentin demonstrated statistically significant improvement in LCQ scores at 2 months (2.48 points, P≤ .01) and 6 months (5.40 points, P = .01) of treatment as compared with baseline. Patients taking TCAs demonstrated statistically significant improvement of LCQ scores at 2 months of treatment (3.46 points, P≤ .01). However, the majority of patients discontinued treatment, most commonly secondary to the development of tachyphylaxis after 2 months, precluding analysis at 6 months.

Conclusion

While both neuromodulator classes demonstrated short-term benefit, the majority of patients discontinue treatment prior to 6 months, with patients taking TCAs discontinuing more frequently than patients on gabapentin. Future investigations are warranted evaluating tachyphylaxis and the utility of dual treatment therapies designed to address peripheral and central sensory pathways involved in UCC.

Research highlights from the 2017 ERS International Congress: airway diseases in focus

For another year, high-quality research studies from around the world transformed the annual ERS International Congress into a vivid platform to discuss trending research topics, to produce new research questions and to further push the boundaries of respiratory medicine and science. This article reviews only some of the high-quality research studies on asthma, chronic obstructive pulmonary disease (COPD), bronchiectasis and chronic cough that were presented during the congress through the Airway Diseases Assembly (ERS Assembly 5) and places them into the context of current knowledge and research challenges.

Members of the @ERStalk Airway Diseases Assembly discuss clinical highlights from #ERSCongress 2017http://ow.ly/G51Y30i7fMR

Risks and Cough-Aggravating Factors in Prolonged Cough. Epidemiological Observations from the Nagahama Cohort Study

RATIONALE

Chronic cough hypersensitivity, a potentially important concept of chronic or prolonged cough, is featured by heightened cough response to low-intensity stimuli, which may be generated in the absence of airflow limitations or allergic conditions. However, there is little epidemiological evidence to support this.

OBJECTIVES

In this large-scale community survey, we aimed to determine risks and cough-aggravating factors of prolonged cough while focusing on serum IgE levels.

METHODS

Prevalence of prolonged cough, defined as cough lasting 3 weeks or longer, was determined in 9,804 residents from a baseline measurement of the Nagahama Cohort Study, conducted from 2008 to 2010. Risk assessment of prolonged cough was confined to subjects without asthma (n = 9,402). A follow-up measurement of the Nagahama Study was successively conducted from 2013 to 2015, recruiting the same residents living in Nagahama City, Japan (n = 8,292). Validation analysis was performed in the follow-up measurement.

RESULTS

In a baseline measurement, prolonged cough was reported by 9.5% of subjects without asthma and 32.3% of subjects with asthma. In subjects without asthma, various cough-aggravating factors were associated with prolonged cough. On the multivariate analysis, several cough-aggravating factors, including nighttime or early morning, weather, pollen season, and common cold, were associated with prolonged cough, independent of female sex, younger age, chronic obstructive pulmonary disease, postnasal drip, daytime sputum, and lower serum total IgE. Serum-specific IgE levels against Japanese cedar pollen were significantly higher in subjects who responded "yes" to "cough in the pollen season" than in those who did not respond, whereas, among subjects who responded "yes" to "cough in the pollen season," prolonged coughers showed lower serum IgE levels against Japanese cedar pollen than temporal coughers. Validation analysis in a follow-up measurement confirmed the associations between prolonged cough and cough-aggravating factors observed in the baseline measurement.

CONCLUSIONS

The presence of several cough-aggravating factors in the absence of severe allergic conditions may support the presence of cough hypersensitivity.

Cough and airway disease: The role of ion channels

Cough is the most common reason for patients to visit a primary care physician, yet it remains an unmet medical need. It can be idiopathic in nature but can also be a troublesome symptom across chronic lung diseases such as asthma, COPD and idiopathic pulmonary fibrosis (IPF). Chronic cough affects up to 12% of the population and yet there are no safe and effective therapies. The cough reflex is regulated by vagal, sensory afferent nerves which innervate the airway. The Transient Receptor Potential (TRP) family of ion channels are expressed on sensory nerve terminals, and when activated can evoke cough. This review focuses on the role of 4 TRP channels; TRP Vannilloid 1 (TRPV1), TRP Ankyrin 1 (TRPA1), TRP Vannilloid 4 (TRPV4) and TRP Melastatin 8 (TRPM8) and the purinergic P2X3 receptor and their possible role in chronic cough. We conclude that these ion channels, given their expression profile and their role in the activation of sensory afferents and the cough reflex, may represent excellent therapeutic targets for the treatment of respiratory symptoms in chronic lung disease.

Cough in idiopathic pulmonary fibrosis

Many patients with idiopathic pulmonary fibrosis (IPF) complain of chronic refractory cough. Chronic cough is a distressing and disabling symptom with a major impact on quality of life. During recent years, progress has been made in gaining insight into the pathogenesis of cough in IPF, which is most probably "multifactorial" and influenced by mechanical, biochemical and neurosensory changes, with an important role for comorbidities as well. Clinical trials of cough treatment in IPF are emerging, and cough is increasingly included as a secondary end-point in trials assessing new compounds for IPF. It is important that such studies include adequate end-points to assess cough both objectively and subjectively. This article summarises the latest insights into chronic cough in IPF. It describes the different theories regarding the pathophysiology of cough, reviews the different methods to assess cough and deals with recent and future developments in the treatment of cough in IPF.

Airway Hypersensitivity, Reflux, and Phonation Contribute to Chronic Cough

BACKGROUND & AIMS

Although chronic cough is common, its etiology is often elusive, making patient management a challenge. Gastroesophageal reflux and airway hypersensitivity can cause chronic cough. We explored the relationship between reflux, phonation, and cough in patients with idiopathic chronic cough.

METHODS

We performed a blinded, cross-sectional study of nonsmoking patients with chronic cough (duration, >8 weeks) refractory to reflux treatment referred to the Digestive Disease Center at Vanderbilt University. All underwent 24-hour acoustic recording concurrently and temporally synchronized with ambulatory pH-impedance monitoring. Cough, phonation, and pH-impedance events were recorded. We evaluated the temporal relationship between cough and phonation or reflux events using Poisson and logistic regression.

RESULTS

Seventeen patients met the inclusion criteria (88% female; 100% white; median age, 63 years [interquartile age range, 52-66 years]; mean body mass index, 30.6 [interquartile range, 27.9-34.0]); there were 2048 analyzable coughing events. The probability of subsequent coughing increased with higher burdens of preceding cough, reflux, or phonation. Within the first 15 minutes after a cough event, the cough event itself was the main trigger of subsequent cough events. After this period, de novo coughing occurred with increases of 1.46-fold in association with reflux alone (95% confidence interval, 1.17-1.82; P < .001) and 1.71-fold in association with the combination of phonation and reflux events.

CONCLUSIONS

Antecedent phonation and reflux increased the rate of cough events in patients with idiopathic chronic cough. Reflux events were more strongly associated with increased rate of coughing. Our findings support the concept that airway hypersensitivity is a cause of chronic cough, and that the vocal folds may be an effector in chronic cough ClinicalTrials.gov number: NCT01263626.