Cough Hypersensitivity Syndrome: New Paradigm in Explaining Chronic Cough
The human body is very intelligently designed such that it contains natural mechanisms to eliminate irritants. If nasty bacteria get in your system, your white blood cells do their best to try to stop them before they wreak havoc. When you get insect bites, your immune system acts on it, resulting in that red bump in your skin.
Our respiratory systems have a similar defense mechanism. We cough when we want to expel irritants from our lungs or throat. Yet, despite being protective, the cough reflex can become a hypersensitive response of the body.
This article will talk about the new paradigm of cough hypersensitivity syndrome. By understanding this condition, we can better understand the pathogenesis of this cough dysfunction and help produce new medical therapy for affected individuals.
Defining Cough Hypersensitivity Syndrome
Cough hypersensitivity syndrome is a distinct clinical syndrome characterized by chronic coughing. This syndrome’s triggers usually include minor thermal changes, and chemical or mechanical exposure. For example, tobacco smoke and perfume exposure provoke a persistent cough in sufferers.
Right now, the condition is a “syndrome,” so it is a conglomeration of various symptoms, which will be explored later. This syndrome encompasses different medical conditions where chronic cough is the central complaint. Some of the symptoms associated with cough hypersensitivity syndrome include irritation in the chest or throat, voice hoarseness, and being triggered by external irritants.
If you often see patients in a medical setting, coughs are likely one of the most common medical complaints that you will face. And, while we have been more cautious of cough symptoms due to the pandemic, this is not something new..
Based on a survey, patients from the US said that an acute cough was a common reason for going to the doctor. The same results are seen in Asia-Pacific countries. Chronic coughs are also common — roughly 10% of adults worldwide have one at any given moment. Persistent coughs particularly continue to be an epidemiological problem for the elderly, in whom they become more common.
At first, you might consider a cough a simple symptom. However, a chronic cough can impair a person’s quality of life. This is especially true in cases where the cough manifests in other diseases like upper airway cough syndrome, cough-variant asthma, or interstitial lung disease. Pulmonary and respiratory diseases are not simple cases that can be left unattended to.
Additionally, the latest studies now say that chronic cough patients experience a variety of psychological, physical, and social consequences. Elderly chronic cough patients can suffer from debilitated mental health similar to stroke or Parkinson’s disease patients.
Modern medicine must always be reassessing its paradigms. During the past few years, the explanation regarding chronic cough is that it is mainly the reaction of your respiratory system to some diseases. It used to be associated with cough-variant asthma and gastroesophageal reflux disease.
However, medical researchers have been surprised to see that not many sufferers of those diseases actually have a chronic cough. The association between the two is weaker than previously thought, and perspectives on chronic coughs are changing.
The unexplained nature of chronic coughs that does not belong to other reactionary conditions has paved the way for the concept of cough hypersensitivity syndrome.
What Causes Cough Hypersensitivity?
Now and then, we all experience bouts of persistent coughing. It may be due to weather changes, or exposure to lots of dust and pollen. However, hypersensitivity of one’s cough reflex is different from what you usually encounter.
Many pulmonary disorders are characterized by disordered sensory processing. The condition happens when the brain becomes confused regarding sensory information.
Disordered sensory processing is one of the suggested causes of cough hypersensitivity syndrome. The afflicted individual experiences a chronic and continuous need to cough. Unfortunately, the process behind how the airway sensory circuits become disrupted, particularly at the central nervous system level, is unknown.
A current theory of many researchers is that there is abnormal neurology behind persistent cough syndrome. We will have to watch how medical research comes up with an evidence-based answer to this syndrome.
Despite the dearth of etiological theory, cough hypersensitivity syndrome has been proposed to explain why some illnesses that normally cause a self-limiting cough begin to manifest as something chronic. This hypothesis holds the syndrome as a medical condition that overrides other illnesses related to coughing.
To sum it up, there are two group of thought. One says cough hypersensitivity syndrome may occur in isolation, where the syndrome itself causes the persistent cough. In contrast, the other school of thought says that the syndrome overlaps with other conditions, like eosinophilic bronchitis, pulmonary fibrosis, cough variant asthma, causing normally short-term coughs to become chronic due to the person’s neurological makeup.
With this new theory and syndrome, we can see that coughing can, in itself, be considered more than a symptom of another disease and instead a distinct clinical condition.
Cough Hypersensitivity Syndrome: A New Paradigm
Cough hypersensitivity syndrome is a relatively new paradigm that accounts for unexplained coughing. People are diagnosed with it if they suffer from a chronic and idiopathic cough. Individuals can also be diagnosed with this syndrome if they have a heightened sensitivity to inhaled cough-provoking stimuli like citric acid or capsaicin.
To help understand this new paradigm, the diagram above shows how the cough hypersensitivity syndrome overlaps with different diseases. The following factors are closely intertwined with the condition:
- Rhinitis
- ACE inhibitors
- Cigarette smoke
- Pulmonary diseases
- Reflux diseases
- Asthma or eosinophilic bronchitis
The diagram shows cough hypersensitivity syndrome can be explained as a general term encompassing different cough-related diseases, but, more importantly, more than that. The syndrome is a new perspective on the times when someone has a chronic cough but none of these traditional underlying diseases. Cough hypersensitivity syndrome has a unique pathophysiology, developing independent of other diseases. Unfortunately, the pathophysiology of the syndrome is currently debated.
Evidence For Neuropathology in Cough Hypersensitivity
Cough hypersensitivity is a very new paradigm, and researchers are still struggling to provide concrete evidence for the neuropathological explanation of the condition. One reason cited for such difficulty is the lack of adequate human neural tissues to act as a sample for testing in a laboratory setting.
Nevertheless, neuropathology is the mechanism that seems most accurate in explaining how cough hypersensitivity syndrome happens. When the afflicted individual’s sensory neural pathway is functioning aberrantly, for example impaired and unmanaged cough reflex regulation, consequences can include this condition. .
Various sensory nerves react when we are exposed to irritants, like viruses or allergens. The irritants, also called peripheral inputs, initiate cough responses due to changes that occur in the nerves.
The cough reflex aims to remove any viruses — it partially evolved as a defensive mechanism against them. However, the opposite often occurs. Respiratory viruses infect the host’s airway, causing neurogenic inflammation triggered by the host’s immune system. The vessel dilates, immune cells accumulate in the site, become activated, and eventually cause eosinophilic airway inflammation. Simultaneously, a cascade of phenotypic changes, like firing up sensory receptors, induces the cough and promotes further inflammation of the airway. This inflammation causes a negative feedback loop because it is perceived by the activated receptors as further irritants to expel.
Essentially, because of this cascade of events, the individual suffers from chronic cough because the hypersensitive cough response creates and maintains a vicious cycle of repeating itself.
Clinical trial evidence backs up this new paradigm. Drugs primarly used for treating neuropathic pain have been discovered to have antitussive effects in cough hypersensitivity cough syndrome suffers. Their neuro-modulatory qualities are thought to be the mechanism behind this cough reduction, as they do not have any more traditional antitussive properties.
A European group conducted a study wherein they interviewed respiratory medicine professionals to examine the clinical relevance of cough hypersensitivity syndrome. All participants agreed that cough hypersensitivity is a therapeutically valuable paradigm, and there was a high degree of agreement in the responses.
Additionally, non-pharmacological speech pathology therapy, which is thought to operate on both the peripheral and central components of the cough reflex system, has demonstrated considerable improvements in reducing cough outcomes.
Clinical Implications of Cough Hypersensitivity Syndrome
It is essential to understand this syndrome’s clinical implications.
One avenue to consider is understanding its relation with asthma. Type 2 airway inflammation, common in asthma, can lead to cough hypersensitivity. Asthma is very complicated, and working out its pathophysiology can be tricky, especially if the patient is already under medication that targets and therefore affects their symptoms. Based on a survey conducted on patients diagnosed with asthma, even when their cough frequency is managed through medication when their asthma is being medicated, it does not necessarily mean that their airway obstruction and inflammation subside as well along with it. Therefore, patients need a diagnostic tool like sputum analysis or exhaled nitric oxide test to detect their airway inflammation so it can be treated.
This survey’s data imply that coughing and base characteristics like lung function and inflammation substantially contribute to how asthma happens. However, the tools we have now that assess the effectiveness of controlling asthma are not designed to tell us how cough affects the manifestation of asthma. To better understand the clinical significance of cough in asthma, cough-specific examination and therapy are necessary.
Similarly, other conditions like idiopathic pulmonary fibrosis or bronchiectasis are being assessed regarding the clinical impact of cough hypersensitivity syndrome on these conditions.
Common to almost all conditions that researchers are trying to assess is the need for an accurate and specific measurement tool that would validate how coughing interacts with conditions.
How Do You Treat Coughing Caused by This Syndrome?
The survey by the European group of pulmonologists, mentioned above, also revealed another critical issue with the cough hypersensitivity syndrome that has a significant impact on the patients — both quality of life and morbidity are strongly associated with chronic cough.
The same survey revealed that management of chronic cough is not talked about much. In fact, treating chronic coughs was one of the most requested topics to focus on. This involves better treatment options for the patients, increased support from the medical field, and improvement in treatment centers for access.
Of course, to begin treating hypersensitivity cough, it is essential to know which patients fall within this condition. Normally, patients are thought to have cough hypersensitivity syndrome when they have a negative diagnostic workup along with a failed attempt to relieve their cough with different approaches. This condition can also be sometimes referred to as sensory neuropathic cough.
In most cough hypersensitivity cases, the cause of the condition is unknown. Hence, it is thought to be idiopathic in nature where no underlying cause can be immediately pinpointed. Even though the underlying process is unknown, treatment for hypersensitivity cough is neuromodulator therapy.
Gabapentin and tricyclic antidepressants are medications that can be used to address this condition because it works on neuromodulation once taken in. The common antidepressant medications that doctors can reach out to are amitriptyline and nortriptyline.
Gabapentin has been proven to enhance the quality of life in individuals with chronic refractory cough. This medication, therefore, indicates its role in central reflex sensitization in this disease. It is critical to inform patients about potential adverse effects and have a procedure to facilitate therapy titration. Early referral to a speech pathology professional is also another treatment option. For the treatment of persistent cough, this therapy is an effective non-pharmacological option.
Conclusion
Coughing is an important defense mechanism of the body. It is dependent on a complicated vagally mediated neural circuit that is only partially understood. But it can get debilitating at some point!
Cough hypersensitivity syndrome is induced in various illnesses. Because of a viral respiratory infection, or just a chronic cough, the patient will suffer from excessive coughing. Unfortunately, you would not want your patients to suffer from this because it impairs their quality of life and could harm their overall health in the long run.
Over the last several years, medical researchers have come a long way in understanding the mechanism of cough hypersensitivity and realizing that it’s a separate clinical syndrome. More recently, therapeutic developments have raised the prospect of novel medicines to understand this condition entirely.
If you are working closely with patients whose diagnosis is probably cough hypersensitivity syndrome, you can help your patients track their coughing symptoms. Fortunately, Hyfe is here to provide you with a top-notch cough tracking system. You need to explore the Hyfe app and let it do the magic for you. Track your patients’ hypersensitivity cough so that you can develop better management of their conditions. You and your patients will benefit from this fantastic tracking app in no time.
