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Understanding Chronic Cough: Causes, Pathogenesis, and Implications
Chronic Cough: Definition and Global Impact
Chronic cough, defined as a cough lasting more than eight weeks, is a prevalent condition that significantly impairs quality of life. It is a common symptom that affects a large proportion of the general population, with a high global epidemiological burden. Chronic cough can be a consequence of various diseases such as asthma, rhinitis, and gastro-oesophageal reflux disease (GERD). However, recent evidence suggests that chronic cough is a clinical syndrome characterized by neuronal hypersensitivity.
Common Causes of Chronic Cough
Asthma and Cough-Variant Asthma (CVA)
Asthma is one of the most common causes of chronic cough, particularly in adult nonsmokers. Cough-variant asthma (CVA) is a form of asthma where the cough is the predominant or sole symptom, without the typical asthmatic symptoms like wheezing or dyspnea. Diagnosis of CVA can be challenging as physical examination and spirometry findings may be normal, and it often requires methacholine inhalation challenge testing to demonstrate bronchial hyperresponsiveness.
Upper Airway Cough Syndrome (UACS)
Previously known as postnasal drip syndrome, UACS is another frequent cause of chronic cough. It is associated with a variety of rhinosinus conditions and can be present alone or in combination with other conditions like asthma and GERD.
Gastroesophageal Reflux Disease (GERD)
GERD is a significant contributor to chronic cough. The reflux of stomach acids into the esophagus can trigger a cough reflex, leading to chronic cough in the absence of other symptoms.
Pathogenesis and Mechanisms
Chronic cough is often associated with an increased response to tussive agents such as capsaicin, indicating heightened sensitivity of the cough reflex. This hypersensitivity can be due to plastic changes in the intrinsic and synaptic excitability in the brainstem, spine, or airway nerves, which can persist even after the initial cause of the cough has been resolved. Structural and inflammatory changes in the airway mucosa may also play a role in non-asthmatic chronic cough.
Determinants and Risk Factors
Several factors are associated with chronic cough, including asthma, rhinitis, tobacco smoking, environmental tobacco smoke, and obesity. Females are more likely to report nocturnal and nonproductive cough compared to males. Additionally, exposure to environmental pollution, especially particulates, is a significant risk factor.
Habit Cough Syndrome in Children
Habit cough syndrome (HC) is a functional cough without an organic basis, often seen in children and adolescents. It is characterized by repetitive coughing that is absent during sleep and can be effectively treated with behavioral measures such as suggestion therapy. This condition highlights the importance of recognizing functional coughs to avoid unnecessary medical interventions.
Complications and Patient Harm
Cough can lead to a wide range of complications affecting various systems, including the upper airways, chest wall, thorax, abdominal wall, heart, central nervous system, and more. These complications can range from trivial issues like lightheadedness to severe, life-threatening conditions such as cervical artery dissection. Chronic cough can also cause significant emotional and psychological harm, including anxiety and insomnia, further impacting the patient's quality of life.
Conclusion
Chronic cough is a multifaceted condition with various underlying causes and significant implications for patient health and quality of life. Understanding the common causes, pathogenesis, and potential complications is crucial for effective diagnosis and management. Addressing both the underlying conditions and the heightened sensitivity of the cough reflex is essential for comprehensive treatment. Future research should focus on standardizing definitions and exploring prospective studies to better understand and manage chronic cough.
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