Approach to chronic cough: the neuropathic basis for cough hypersensitivity syndrome

The Application of Superior Laryngeal Nerve Block for Non-Cough Laryngeal Hypersensitivity

OBJECTIVE(S)

To investigate the effect of superior laryngeal nerve (SLN) block in patients with non-cough complaints relating to laryngeal who have failed conventional medical therapy.

METHODS

Retrospective chart review of 46 patients who underwent SLN block for non-cough indications between July 2019 and March 2022 was performed. Demographics, comorbidities, and patient-reported outcomes were collected. The primary diagnoses for this group included: odynophagia, throat pain, cervicalgia, muscle tension dysphonia, globus sensation, hyoid bone syndrome, and Eagle syndrome.

RESULTS

The cohort underwent an average of 1.24 bilateral injections (range 0-7) and 0.87 unilateral injections (range 0-4). About 35 of 46 patients reported an average of 51.0% improvement in their symptoms, with the treatment effect lasting 7.60 weeks on average. On subgroup analysis, the patients with spasmodic dysphonia, odynophagia, and hyoid bone syndrome had the best percent improvement on average (75%-77.5%). Patients with globus sensation had the lowest percent improvement on average in response to this therapy, reporting only about 25%. Five patients experienced a mild adverse reaction immediately following injection which resolved spontaneously.

CONCLUSION

The use of in-office SLN block for non-cough disorders involving the larynx requires further study with larger sample sizes to better delineate the efficacy of these applications.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:1765-1768, 2024.

The Role of Bilateral Superior Laryngeal Nerve Block in Managing Refractory Chronic Cough

OBJECTIVE(S)

The aim was to investigate the utilization and efficacy of bilateral superior laryngeal nerve block in patients with refractory chronic cough.

METHODS

A retrospective chart review of 164 patients with refractory chronic cough who underwent bilateral SLN block at a single institution between November 2018 and September 2022 was performed. Demographics, comorbidities, and patient-reported outcomes including pre- and postinjection Leicester Cough Questionnaire (LCQ) scores were collected and analyzed.

RESULTS

The cohort underwent an average of 2.97 bilateral injections (range 1-22), containing either corticosteroid and local anesthetic or corticosteroid alone. Notably, 116 of 164 of patients reported an average of 67.3% reduction in their symptoms, with the treatment effect lasting 7.60 weeks on average. The average pre- and postinjection LCQ scores were 9.70 and 13.82, respectively. A lower LCQ score represents a greater impairment of health status due to cough, and the minimum important change is 1.3 points between questionnaires. The average improvement on LCQ following bilateral SLN block was 4.11 points for this cohort.

CONCLUSION

The use of in-office bilateral SLN block is an effective treatment that can be used alone or in conjunction with oral medications for the treatment of refractory chronic cough.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:1773-1777, 2024.

Identifying Practice Gaps Among Otolaryngology Providers for the Treatment of Chronic Cough

Objective

Increasing evidence over the last decade suggests that many cases of unexplained chronic cough (UCC) have a neurogenic etiology, with laryngeal hypersensitivity (LH) being identified as a key mechanism. Official guidelines since 2015 have adopted use of neuromodulators and adjuvant speech therapy as a result, but historically implementation of guidelines is slow. Our survey aimed to investigate gaps in diagnosis and management practices of otolaryngology providers in caring for patients with UCC.

Study Design

Cross-sectional study.

Setting

Survey.

Methods

12-item survey was distributed to 110 otolaryngology practitioners experienced in diagnosis and treatment of chronic cough at a regional otolaryngology continuing education conference. Statistical analysis included Kendall's Tau Rank Correlation to measure the ordinal association between responses to questions, and Fisher's exact test to determine if there were associations between responses and years of career experience.

Results

Forty eligible respondents underwent subsequent analysis. There was no association between frequency of identifying LH as a primary etiology and use of neuromodulators (τ = 0.23, P = .10). However, there was a significant correlation between LH and referrals to speech therapy (τ = 0.27, P = .05). Fisher's exact test did not reveal any significant differences among any responses based on practitioner experience.

Conclusion

Our results indicate a possible disparity in treatment of UCC with neuromodulators and the utilization of speech therapy despite guideline recommendations advocating for neuromodulators with adjuvant speech therapy. Further research with larger sample sizes and more specific inquiries is necessary to elucidate this association and control for any regional differences.

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.

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 Toxicity of Wiped Dust and Airborne Microbes in Individual Classrooms Increase the Risk of Teachers' Work-Related Symptoms: A Cross-Sectional Study

Background: The causes and pathophysiological mechanisms of building-related symptoms (BRS) remain open. Objective: We aimed to investigate the association between teachers’ individual work-related symptoms and intrinsic in vitro toxicity in classrooms. This is a further analysis of a previously published dataset. Methods: Teachers from 15 Finnish schools in Helsinki responded to the symptom survey. The boar sperm motility inhibition assay, a sensitive indicator of mitochondrial dysfunction, was used to measure the toxicity of wiped dust and cultured microbial fallout samples collected from the teachers’ classrooms. Results: 231 teachers whose classroom toxicity data had been collected responded to the questionnaire. Logistic regression analysis adjusted for age, gender, smoking, and atopy showed that classroom dust intrinsic toxicity was statistically significantly associated with the following 12 symptoms reported by teachers (adjusted ORs in parentheses): nose stuffiness (4.1), runny nose (6.9), hoarseness (6.4), globus sensation (9.0), throat mucus (7.6), throat itching (4.4), shortness of breath (12.2), dry cough (4.7), wet eyes (12.7), hypersensitivity to sound (7.9), difficulty falling asleep (7.6), and increased need for sleep (7.7). Toxicity of cultured microbes was found to be associated with nine symptoms (adjusted ORs in parentheses): headache (2.3), nose stuffiness (2.2), nose dryness (2.2), mouth dryness (2.8), hoarseness (2.2), sore throat (2.8), throat mucus (2.3), eye discharge (10.2), and increased need for sleep (3.5). Conclusions: The toxicity of classroom dust and airborne microbes in boar sperm motility inhibition assay significantly increased teachers’ risk of work-related respiratory and ocular symptoms. Potential pathophysiological mechanisms of BRS are discussed.

Safety and efficacy of gefapixant, a novel drug for the treatment of chronic cough: A systematic review and meta-analysis of randomized controlled trials

AIM

We conducted this systematic review and meta-analysis to investigate the efficacy and safety of gefapixant, a novel P2X3 receptor antagonist, in patients with chronic cough.

METHODS

We searched four databases for randomized controlled trials (RCTs). We assessed the cough frequency, severity, total Leicester cough questionnaire (LCQ) score, and adverse events. We analyzed the data using Open Meta-Analyst and Review Manager Software.

RESULTS

We included four unique studies (comprising five stand-alone RCTs) with 439 patients. Compared to placebo, gefapixant had positive anti-tussive effects by improving awake cough frequency (mean difference [MD] = -5.27, 95% confidence interval [CI] [-6.12, -4.42], P < 0.00001), night cough frequency (MD = -3.71, 95% CI [-6.57, -0.85], P = 0. 01), 24 h cough frequency (MD = -4.18, 95% CI [-5.01, -3.36], P < 0.00001), cough severity using the Visual Analog Scale (MD = -13.36, 95% CI [-17.80, -8.92], P < 0.00001), cough severity diary (MD = -0.88, 95% CI [-1.25, -0.51], P < 0.00001), and total LCQ score (MD = 2.00, 95% CI [1.15, 2.86], P = 0. 00001). Meta-regression analyses showed a positive correlation between the gefapixant dose and the incidence of any adverse event (relative risk [RR] = 0.239, 95% CI [0.093, 1.839], P = 0.001) and incidence of adverse event related to treatment (RR = 0.520, 95% CI [0.117, 0.922], P = 0.011).

CONCLUSIONS

In patient with chronic cough, gefapixant exhibits favorable anti-tussive outcomes by improving the cough frequency, severity, and quality of life. While gefapixant is largely tolerable, its side effects (notably taste alteration) are dose dependent.

Longitudinal Follow-up of Superior Laryngeal Nerve Block for Chronic Neurogenic Cough

Objective

To demonstrate longitudinal follow-up for patients who underwent in-office superior laryngeal nerve (SLN) block with lidocaine and steroids for chronic neurogenic cough.

Study Design

Longitudinal follow-up study over 10 months.

Setting

Clinical.

Methods

A retrospective review of 30 patients who underwent in-office nerve block to the SLN for neurogenic cough, including the 10 patients whose outcomes were originally published in 2019.

Results

Thirty patients in this study who underwent a series of SLN blocks showed significant improvement in cough severity index (CSI). The average number of blocks was 3 (range, 2-8). Twelve patients underwent initial SLN block to the left side and 18 patients underwent initial SLN block to the right side. The mean follow-up from the first SLN block was 5.3 months. The mean pretreatment and posttreatment CSI scores were 27 and 11, respectively, for all 30 patients who underwent an SLN block. A Wilcoxon signed rank test shows that there is a significant effect on CSI (W = 2, z = −4.659, P < .05). The mean longitudinal follow-up for the original 10 patients was 10 months from the first SLN block, with none of these patients receiving any further treatment for their cough.

Conclusion

Superior laryngeal nerve block is an effective long-term treatment for neurogenic cough. No additional treatment was required within 10 months of the SLN block.

Level of Evidence

Level IV.

Is laryngeal hypersensitivity the basis of unexplained or refractory chronic cough?

Refractory chronic cough (RCC) and unexplained chronic cough (UCC) are common problems seen in primary care and subspecialty clinics. The role of cough hypersensitivity and laryngeal dysfunction in contributing to the persistence of cough in RCC/UCC is not well recognised. Data of patients with RCC and UCC evaluated in 2019 by an interdisciplinary cough clinic led by a pulmonologist and speech-language pathology team was reviewed. Patients completed validated questionnaires including the Leicester cough questionnaire (LCQ), voice handicap index (VHI) and dyspnoea index (DI) questionnaire at initial encounter. Presence of cough hypersensitivity was based upon a history of allotussia and hypertussia. Laryngeal dysfunction was diagnosed in those with a history of laryngeal paresthesias, throat clearing, voice abnormalities, upper airway dyspnoea and documentation of functional or anatomic laryngeal abnormalities on nasoendoscopy. Of the 60 UCC/RCC patients analysed, 75% of patients were female and 85% were over 40 years of age. Cough hypersensitivity was documented in all patients and multiple cough triggers occurred in 75% of patients. 95%, 50% and 25% of patients reported laryngeal paresthesias, voice abnormalities and upper airway dyspnoea, respectively. Significant associations between LCQ and VHI and DI scores occurred when adjusting for age, sex, ethnicity and body mass index. Laryngeal functional abnormalities were documented on 44 out of 60 patients on nasoendoscopy. Hypertussia, allotussia and laryngeal dysfunction are common in patients with RCC and UCC. Evaluation of UCC and RCC can delineate laryngeal hypersensitivity and allows appropriate treatment to be directed at this phenotype.

Cough responses to inhaled irritants are enhanced by eosinophil major basic protein in awake mice

A distinct association between airway eosinophilia and chronic cough is well documented. Eosinophil granule-derived cationic proteins, such as major basic protein (MBP), have been shown to activate and enhance the excitability of bronchopulmonary C-fiber sensory nerves, which may then lead to an increase in cough sensitivity. This study was carried out to determine whether cough responses to inhaled irritant gases were altered by delivery of MBP into the airways. An awake mouse moved freely in a recording chamber that was ventilated with a constant flow of air or irritant gas mixture. Cough responses to separate inhalation challenges of sulfur dioxide (SO₂; 300 and 600 ppm) and ammonia (NH₃; 0.1 and 0.2%), each for 5-min duration, were measured daily for 3 days before and for up to 8 days after MBP (10-20 µg) instillation into the trachea. During control, inhalations of SO₂ and NH₃ consistently elicited cough responses in a dose-dependent manner. After MBP treatment, cough responses to both SO₂ and NH₃ increased significantly and progressively and reached peaks 2-3 days after the treatment before returning to control level in 3-7 days. In sharp contrast, cough responses to these irritant gases were not affected by the treatment with the vehicle of MBP. These results suggest that the MBP-induced lingering elevation of cough responsiveness may be a contributing factor in the pathogenesis of chronic cough associated with eosinophilic infiltration of the airways.

Cough-Related Laryngeal Sensations and Triggers in Adults With Chronic Cough: Symptom Profile and Impact

Purpose

Recent evidence suggests that cough hypersensitivity may be a common feature of chronic cough in adults. However, the clinical relevance remains unclear. This study evaluated the cough-related symptom profile and the clinical relevance and impact of cough hypersensitivity in adults with chronic cough.

Methods

This cross-sectional multi-center study compared cough-related laryngeal sensations and cough triggers in patients with unexplained chronic cough following investigations and in unselected patients newly referred for chronic cough. A structured questionnaire was used to assess abnormal laryngeal sensations and cough triggers. Patients with unexplained cough were also evaluated using the Leicester Cough Questionnaire (LCQ) and a cough visual analogue scale (VAS), and these scores were assessed for correlations with the number of triggers and laryngeal sensations.

Results

This study recruited 478 patients, including 62 with unexplained chronic cough and 416 with chronic cough. Most participants reported abnormal laryngeal sensations and cough triggers. Laryngeal sensations (4.4 ± 1.5 vs. 3.9 ± 1.9; P = 0.049) and cough triggers (6.9 ± 2.6 vs. 5.0 ± 2.8; P < 0.001) were more frequent in patients with unexplained chronic cough than in those with chronic cough. The number of triggers and laryngeal sensations score significantly correlated with LCQ (r = −0.51, P < 0.001) and cough VAS score (r = 0.53, P < 0.001) in patients with unexplained chronic cough.

Conclusions

Cough hypersensitivity may be a common feature in adult patients with chronic cough, especially those with unexplained chronic cough. Cough-related health status and cough severity were inversely associated with the number of triggers and laryngeal sensations, suggesting potential relevance of assessing cough hypersensitivity in chronic cough patients.

Altering cough reflex sensitivity with aerosolized capsaicin paired with behavioral cough suppression: a proof-of-concept study

Background

The purpose of this prospective, quasi-experimental, single cohort proof-of-concept study was to determine feasibility and proof-of-concept of programmatically decreasing cough sensitivity through use of cough suppression strategies following inhalation of aerosolized capsaicin, in gradually increasing doses, across repeated treatment sessions.

Methods

Five healthy adults, ages 20-32 years of age, enrolled and completed the study. The study commenced in three phases. Phase I consisted of baseline cough sensitivity testing using pharmaceutical-grade aerosolized capsaicin, delivered via a Koko DigiDoser with nebulizer. The single-inhale, dose-response method was used. Doses that elicited two coughs (C2) and five coughs (C5) were recorded. Testing ceased when participants met the C5 threshold or when they had been given the maximum dose of 1,000 µmol/L. Phase II consisted of 5-6 treatment sessions, during which participants were exposed to increasing doses of aerosolized capsaicin while implementing behavioral cough suppression strategies. In phase III, cough sensitivity was re-tested at 1 and 3 weeks post-treatment. Participants were given explicit instructions to not try to suppress their cough. Participants who did not reach the C2 or C5 threshold at 1,000 µmol/L were assigned a score of 1,250 µmol/L.

Results

Each participant demonstrated a gradual increase in maximum capsaicin dose suppressed during each treatment session, with each successfully suppressing at 1,000 µmol/L by the final treatment session. C2 was greater than baseline in 4 of the 5 participants at 1 week post-treatment, and in 3 of the 5, at 3 weeks post-treatment. C5 was greater in all 5 participants at both post-treatment time points. In fact, 4 of the 5 participants did not reach the C5 threshold during either post-treatment testing sessions. Wilcoxon's Signed Rank Test, using the logC2 and logC5 values, revealed a significant difference relative to baseline in logC5 at 1 week (z=-2.02, P=0.04) and 3 weeks (z=-2.03, P=0.04) post-treatment. The difference in logC2 neared significance at 1 week post-treatment (z=-1.77, P=0.077), but was insignificant at 3 weeks post-treatment (z=-1.46, P=0.144).

Conclusions

This study demonstrates the potential of treating patients with refractory chronic cough (RCC), due to cough hypersensitivity, with a progressive desensitization approach paired with behavioral cough suppression. Additional research is needed using a randomized, placebo-controlled trial with patients with RCC.

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.

An update and systematic review on drug therapies for the treatment of refractory chronic cough

INTRODUCTION

Chronic Cough (CC) is common and often associated with significant comorbidity and decreased quality of life. In up to 50% of cases, the cough is refractory despite extensive investigation and treatment trials. It is likely that the key abnormality in refractory CC is dysfunctional, hypersensitive sensory nerves, similar to conditions such as laryngeal hypersensitivity and neuropathic pain.

AREAS COVERED

The aim of this systematic review is to assess drug therapies for refractory CC. The authors review the current management of CC and provide discussion of the similarities between neuropathic pain and refractory CC. They review repurposed and new pharmacological treatments. Several meta-analyses were performed to compare the efficacy of treatments where possible.

EXPERT OPINION

Repurposed pain medications such as gabapentin and pregabalin reduce the frequency of cough and improve quality of life. Along with speech pathology, they are important and alternate treatments for refractory CC. However, more treatments are needed and the P2X3 ion channel receptor antagonists show the most promise. With a better understanding of neuronal activation and sensitisation and their signal processing in the brain, improved animal models of cough, and the use of validated cough measurement tools, more effective treatments will develop.

Measurement of Cough Aerodynamics in Healthy Adults

IMPORTANCE

Cough is a critical human reflex and also among the most frequent symptoms in medicine. Despite the prevalence of disordered cough in laryngeal pathologies, comprehensive and quantitative evaluation of cough in these patients is lacking.

OBJECTIVE

Herein we seek to establish normative values for cough aerodynamics to provide a population standard for reference in future studies.

DESIGN, SETTING, AND PARTICIPANTS

Healthy subjects were recruited from an outpatient clinic to perform voluntary cough. Subjects were instructed on the technique for maximal voluntary cough production with measurements recorded on pneumotachograph. Fifty-two subjects were studied, including 29 women and 23 men with a mean age of 51.6 and 52.3 years, respectively. Main Outcomes and Measures: Cough peak airflow, peak pressure, and expiratory rise time. Results were stratified by age, gender, and height.

RESULTS

Peak airflow demonstrated significant differences across age, gender, and height, with flow increasing according to increasing height. Peak cough pressure also increased with height and was significantly greater in males versus females. Expiratory rise time, the time from glottal opening to peak airflow, did not vary with age or height but was statistically significantly longer in women.

CONCLUSIONS

Cough aerodynamics can be readily measured objectively in the outpatient setting. Expiratory rise time, peak flow, and peak pressure are important aspects of each cough epoch. Normative data provided herein can be used for future studies of patients with laryngotracheal disorders, and these cough parameters may prove to be simple, accessible, and repeatable outcome measures.

Chronic Non-Productive Cough in Patients With Primary Sjögren's Syndrome

Objectives

This study aims to evaluate the frequency of chronic cough due to dryness in the trachea and the relationship between depression and chronic cough in patients with primary Sjögren's syndrome (pSS).

Patients and methods

Eighty non-smoking patients (7 males, 73 females; mean age 47.6±9.2 years; range 18 to 70 years) with newly diagnosed pSS were included. All patients were evaluated clinically, radiologically, and physiologically. Patients with cough were assessed using the Leicester Cough Questionnaire and visual analog scale. Beck Depression Inventory was used to determine the risk of depression in patients with cough. Patients with asthma, rhinosinusitis, gastrooesophageal reflux, and drug use which cause cough and pulmonary involvement in pSS were excluded.

Results

Non-productive cough was detected in 30 patients (37.5%). Fourteen patients (17.5%) were admitted to the hospital with cough at least once before the diagnosis of pSS. The median time between onset of symptoms and firm diagnosis was 24 months (25-75 interquartile ranges: 3-60 months). A significant difference was observed in the Beck Depression Inventory scores between patients with and without cough. There was a significant negative relationship between Leicester Cough Questionnaire and Beck Depression Inventory scores.

Conclusion

Patients with pSS often have symptoms for a long duration that mimic those of more commonly encountered non-specific pulmonary conditions. Xerotrachea should be considered in the differential diagnosis of chronic cough, especially in patients with normal pulmonary function tests and pulmonary imaging.

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