Nonproductive cough
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Understanding Nonproductive Cough: Causes, Mechanisms, and Associations
Prevalence and Demographics of Nonproductive Cough
Nonproductive cough, characterized by the absence of mucus production, is a common symptom affecting a significant portion of the population. A large-scale study involving 18,277 subjects from 16 countries found that the median prevalence of nonproductive cough was 10.2%. This type of cough is more frequently reported by females compared to males, with an adjusted odds ratio of 1.27.
Neurochemical Alterations and Sensory Nerve Involvement
Research indicates that neurochemical changes in the sensory nerves of the upper airway may contribute to chronic nonproductive cough. Elevated levels of substance P, a neuropeptide, were found in nasal lavage fluids of patients with increased cough sensitivity to inhaled capsaicin. This suggests a neurochemical abnormality in the upper airway, which could be a potential target for therapeutic interventions.
Airway Inflammation and Cellular Infiltration
Chronic nonproductive cough is often associated with airway inflammation. Studies have shown that patients with this condition exhibit significant eosinophil and lymphocyte infiltration in bronchial biopsies. Specifically, eosinophilic bronchitis and lymphocytic bronchitis were identified as underlying causes in many cases. Additionally, increased numbers of mast cells and eosinophils, along with elevated histamine levels, were observed in bronchoalveolar lavage samples from nonasthmatic patients with chronic nonproductive cough.
Associated Conditions and Risk Factors
Nonproductive cough is linked to several treatable and avoidable conditions. Asthma, rhinitis, tobacco smoking, and environmental tobacco smoke are significant contributors. Furthermore, habitual nonproductive coughing has been associated with anxiety and female gender. Gastroesophageal reflux disease (GERD) and bronchial hyperresponsiveness are also notable risk factors.
Diagnostic and Therapeutic Approaches
The capsaicin cough sensitivity test (CCST) and induced sputum test (IST) are valuable tools in diagnosing and predicting the response to inhaled corticosteroids (ICS) in patients with chronic nonproductive cough. These tests, when used alongside the methacholine bronchial provocation test (MBPT), can help identify patients who are likely to benefit from ICS treatment. The absence of sputum neutrophilia has been shown to increase the response rates to ICS therapy, highlighting the importance of comprehensive diagnostic evaluations.
Conclusion
Nonproductive cough is a multifaceted condition with various underlying causes, including neurochemical alterations, airway inflammation, and associated comorbidities. Understanding these mechanisms and their interactions is crucial for effective diagnosis and treatment. By leveraging diagnostic tools like CCST, IST, and MBPT, healthcare providers can better tailor treatments to individual patients, improving outcomes and quality of life.
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