What is a chronic cough? Coughing is a protective respiratory reflex action by the body to clear secretions or foreign bodies from the airways. Coughs are usually divided into 3 categories according to their duration: acute cough, subacute cough and chronic cough. Acute cough lasts <3 weeks, subacute cough 3-8 weeks, and chronic cough ≥8 weeks. What are the common causes of chronic cough? Chronic cough has many causes and can usually be divided into two categories: those with clear lesions on initial X-ray chest radiographs or imaging tests such as chest CT, such as pneumonia, tuberculosis and lung cancer. The other category is those who have no obvious abnormalities on X-ray or CT chest imaging and whose cough is the main or only symptom, which is usually referred to as chronic cough of unknown origin (chronic cough for short). The common causes of this unexplained chronic cough are: cough variant asthma (CVA), postnasal drip syndrome (PNDs), eosinophilic bronchitis, and gastroesophageal reflux cough (GERC). These causes account for 70% to 95% of chronic cough in respiratory medicine outpatient clinics. Other etiologies are less common but are widely involved, such as chronic bronchitis, bronchiectasis, endobronchial tuberculosis, allergic cough (AC), and psychogenic cough. How is chronic cough diagnosed? 1. Take a detailed history and physical examination: pay attention to the nature, timbre, rhythm and duration of cough, triggering or aggravating factors, postural effects, and accompanying symptoms. Understanding the quantity, color, odor and properties of coughing sputum is of great value to the diagnosis. The diagnosis of asthma is suggested when the exhalation croup is detected on physical examination, and if the inspiratory croup is detected, the diagnosis of central lung cancer or endobronchial tuberculosis should be alerted. (1) Induced sputum examination: It is used for the diagnosis of bronchial asthma or lung cancer, and the analysis of cytology and cellular components of induced sputum can assist in the diagnosis. Elevated eosinophils in cytology examination is the main indicator for the diagnosis of EB. (2) Imaging examinations such as X-ray chest film, CT and high-resolution CT line chest film can determine the location, scope and morphology of lung lesions, and even determine their nature and arrive at a preliminary diagnosis. (3) Pulmonary function tests: Ventilation function and bronchodilation test can help diagnose and identify airway obstructive diseases, such as asthma, chronic bronchitis and CVA, etc. (4) Fiberoptic bronchoscopy (referred to as fiberoptic bronchoscopy): it can effectively diagnose lesions in the tracheal lumen, such as bronchopulmonary cancer, foreign body, endotuberculosis, etc. (5) Esophageal 24-h pH monitoring: It can determine the presence of gastroesophageal reflux (GER), and is the most effective method to diagnose GERC. (6) Other tests: Increased eosinophils in peripheral blood suggest parasitic infection and allergic diseases. Allergen skin test (SPT) and serum specific IgE assay can help diagnose allergic diseases and determine the type of allergens. What is the treatment of chronic cough? Chronic cough has a relatively complex etiology and identifying the cause is the key to successful treatment. Most chronic coughs are not associated with infection and do not require antimicrobial therapy. Glucocorticoids should be used with caution if the cause of the cough is unknown or if infection cannot be excluded. (-) CVA: Cough variant asthma is a special type of asthma in which cough is the only or main clinical manifestation without obvious symptoms or signs such as wheezing and shortness of breath, but with airway hyperresponsiveness. Treatment: The principles of CVA treatment are the same as those of asthma treatment. Most patients can receive small doses of glucocorticoids plus beta agonists, and oral glucocorticoid therapy is rarely required. The duration of treatment is not less than 6~8 weeks. (B) PNDs: postnasal drip syndrome is a syndrome in which secretions flow backward into the postnasal and pharyngeal areas, or even backward into the vocal cords or trachea due to nasal diseases, resulting in a cough as the main manifestation. Treatment depends on the underlying disease causing the PNDs. First-generation antihistamines (chlorpheniramine maleate) and decongestants (pseudoephedrine hydrochloride) are preferred for PNDs caused by the following etiologies 1) non-allergic rhinitis. (2) Vasodilatory rhinitis. (3) Year-round rhinitis. (4) Common cold. Most patients develop efficacy within a few days to 2 weeks after initial treatment. Various antihistamines are effective in the treatment of allergic rhinitis. Second-generation antihistamines without sedative effects are preferred, and commonly used drugs are loratadine or asmizole. Nasal inhalation glucocorticoid is the drug of choice for allergic rhinitis, while antibacterial drug therapy is the main drug for acute bacterial sinusitis, and nasal inhalation glucocorticoid and decongestants can be used to reduce inflammation when the effect is poor or there is much secretion. For the treatment of chronic sinusitis, the following primary treatment regimen is recommended: application of antibacterial drugs effective against gram-positive, gram-negative and anaerobic bacteria for 3 weeks; oral first-generation antihistamines and decongestants for 3 weeks; nasal decongestants for 1 week; and nasal inhaled glucocorticoids for 3 months. Negative pressure drainage, puncture drainage or surgery is feasible when internal treatment is ineffective. (iii) EB: eosinophilic bronchitis, a non-asthmatic bronchitis characterized by airway eosinophil infiltration, is an important cause of chronic cough. Therapeutically, EB responds well to glucocorticoid therapy, and the cough disappears or is significantly reduced after treatment. Bronchodilator therapy is ineffective. It is usually treated with inhaled glucocorticoids: beclomethasone dipropionate (250-500 μg per dose) or equivalent doses of other glucocorticoids twice daily for more than 4 weeks. Dry powder inhalers are recommended. Initial treatment can be combined with prednisone orally at 10-20 mg daily for 3-7 d. (iv) GERC: Gastroesophageal reflux disease, which refers to the reflux of gastric acid and other gastric contents into the esophagus, resulting in a cough as the prominent clinical manifestation. Treatment is divided into: (1) lifestyle modification: lose weight, eat less and more meals, avoid oversaturated bedtime, avoid acidic, greasy food and drinks, avoid coffee and smoking. (2) acid control drugs: often choose proton pump inhibitors (such as omeprazole) or H2 receptor antagonists (ranitidine). (3) Gastric stimulants: such as morpholine, etc. (4) Any patient with underlying gastroduodenal disease (chronic gastritis, gastric ulcer, duodenitis or ulcer) with H. pylori infection should be treated accordingly. (5) The duration of medical treatment requires more than 3 months, and generally requires 2-4 weeks to show efficacy. In a few patients with severe reflux, anti-reflux surgical treatment can be considered.