The definition of chronic cough is currently considered to be a cough that lasts for more than 3 weeks without obvious evidence of lung disease, and it is often the only symptom that patients present with. The etiology of chronic cough is one of the common clinical symptoms of the respiratory system. A cough that lasts more than 3 weeks is called a chronic cough. Some scholars consider a cough of 8 weeks to be a chronic cough. The six major causes of chronic cough are: postnasal drip syndrome, cough variant asthma, gastroesophageal reflux, eosinophilic bronchitis, chronic pharyngitis, and psychogenic cough. Wei Min, Department of Respiratory Medicine, Shandong Chest Hospital
Cough variant asthma is the most common chronic cough. The disease has cough as the only symptom, so the clinical features lack specificity and the misdiagnosis rate is very high. Therefore, the possibility of this disease should be thought of for chronic recurrent cough. Since about 50%-80% of children with cough variant asthma can develop typical asthma and about 10%-33% of adults with cough variant asthma can also develop typical asthma, many authors consider cough variant asthma as a precursor manifestation of asthma, therefore early diagnosis and early treatment of cough variant asthma is very important for the prevention of asthma.
The main clinical features are as follows.
(i) Onset population: The incidence is higher in children, and more than 30% of dry cough in children has been found to be associated with cough variant asthma. In adults, the age of onset of cough variant asthma is higher than that of typical asthma, with about 13% of patients older than 50 years and more common in middle-aged women.
(ii) Clinical manifestations: Cough may be the only symptom of asthma, mainly a prolonged and persistent dry cough, often triggered by inhalation of irritating odors, cold air, exposure to allergens, exercise or upper respiratory tract infection, and in some patients without any trigger. It mostly intensifies at night or in the early morning. Some patients have seasonal attacks, mostly in spring and autumn. Most patients have been treated with cough suppressants and antibiotics for a period of time at the time of consultation, with little or no efficacy, while the application of glucocorticoids, anti-allergic drugs, β2 agonists and theophyllines can provide relief.
(iii) History of allergy: Patients themselves may have a more definite history of allergic diseases, such as allergic rhinitis and eczema. Some patients can be traced to a family history of allergy.
(iv) Physical signs: Although they can also have bronchospasm, they mostly occur in the tiny bronchi at the end or transient spasms, so croup is not heard or rarely heard on physical examination.
(v) Laboratory tests.
1. Increased airway reactivity, mostly mild – moderate. The test procedure may induce an irritating cough similar to that at the onset.
2. Lung function impairment is between normal and typical asthma.
3, Skin allergen test may be positive.
4.Serum IgE level is increased.
5.Bronchodilator test may be positive in some patients. When there is a positive reaction, it indicates the presence of certain spasm and obstructive state of airway.
6. Increased peripheral blood eosinophil counts and increased serum ECP levels.
Rhinitis can cause chronic cough
When it comes to chronic cough, many people will immediately think of bronchitis or chronic pharyngitis. However, some experts say that rhinitis is also one of the culprits of chronic cough.
Rhinitis and sinusitis can cause a chronic cough because nasal secretions from the nasopharynx flow back into the throat, where they contain cough-causing factors and irritate the throat or trachea, causing a cough that is medically known as “postnasal drip syndrome”.
Classification and causes
Coughs are usually classified according to their duration into 3 categories: acute, subacute and chronic coughs. Acute cough lasts <3 weeks, subacute cough 3-8 weeks, and chronic cough ≥8 weeks.
1. Acute cough: The common cold is the most common cause of acute cough. Other etiologies include acute bronchitis, acute sinusitis, allergic rhinitis, acute attacks of chronic bronchitis, and bronchial asthma (referred to as asthma).
2. Subacute cough: The most common causes are post-cold cough (also known as post-infectious cough), bacterial sinusitis, asthma, etc.
3. Chronic cough: Chronic cough has more causes and can usually be divided into two categories: one is for those with clear lesions on initial X-ray chest radiographs, such as pneumonia, tuberculosis, lung cancer, etc.; the other is for those with no obvious abnormalities on X-ray chest radiographs and cough as the main or only symptom, which is usually referred to as chronic cough of unknown origin (referred to as chronic cough). The common causes of chronic cough are: cough variant asthma (CVA), postnasal drip syndrome (PNDs), eosinophilic bronchitis (E) and gastro-oesophageal reflux cough (GERC), which account for 70% to 95% of chronic cough in respiratory medicine outpatient clinics. Other etiologies are less common but widely involved, such as chronic bronchitis, bronchiectasis, endobronchial tuberculosis, allergic cough (AC), and psychogenic cough.
Diagnosis and differential diagnosis
Diagnosis
There are no unified diagnostic criteria, and according to the author’s clinical experience, the following can be used as reference criteria for the diagnosis of cough variant asthma.
(a) Recurrent attacks of cough lasting for more than 1 month, with a predominantly dry cough; often worse at night and/or early in the morning or after exercise.
(ii) Cough mostly associated with exposure to irritating odors, cold air, exposure to allergens, or excessive exercise.
(iii) There may be a history or family history of allergic rhinitis or other allergic diseases, positive allergen tests or increased IgE levels.
(iv) Increased airway reactivity.
(v) Antibiotic or allopathic treatment has been ineffective for more than 2 weeks, while anti-allergy treatment or bronchodilators are effective.
(vi) Exclusion of chronic cough caused by other chronic respiratory diseases.
Ancillary diagnostic measures
The possibility of cough variant asthma should be considered when encountering a patient with only a complaint of chronic cough (longer than two weeks). The diagnosis can be confirmed on the basis of detailed history, careful physical examination and summary of clinical features in combination with the following methods.
(a) If the patient’s FEV1 or PEFR measured at the time of consultation is lower than 70% of the normal value, the patient can be made to inhale a bronchodilator, such as 2% albuterol 200 μg, and the above indexes can be retested after 15 minutes; if the improvement rate of FEV1 and PEFR is ≥15%, the diagnosis of the disease can be confirmed.
(b) If the FEV1 and PEFR are ≥ 70% of the normal expected value at the time of the patient’s visit, a bronchial excitation test can be performed with caution.
(c) Measurement of diurnal variation in PEFR over 24 hours for three consecutive days is a simple and effective screening method for the diagnosis of this type of bronchial asthma, and the diagnosis of the disease can be confirmed if the PEFR variability is ≥20%.
Although the measurement of pulmonary function indices is an effective means of early detection of this type of asthma, some studies have found that the frequency of diurnal cough does not correlate with the degree of pulmonary function impairment.
(iv) Diagnostic treatment: For patients with clinical suspicion of cough variant asthma, bronchodilators, including inhaled or oral β2-receptor stimulants and theophyllines, can be tried. If the cough is significantly reduced or disappears, the diagnosis of cough variant asthma is supported; if the efficacy is not significant, inhaled glucocorticoids or oral prednisone (30-40 mg/day) can be switched to cough variant asthma, and most cough variant asthma can be Most cough variant asthma can be significantly relieved within one week, while a few patients need two weeks of treatment to be effective.
Differential diagnosis
Since cough is a non-specific symptom of many diseases, a detailed clinical history, thorough physical examination, chest X-ray or CT, airway reactivity measurements, pulmonary function, electrocardiogram, fiberoptic bronchoscopy and some special tests must be performed to exclude other diseases that can cause chronic, persistent cough.
Many diseases with cough symptoms need to be differentiated from cough variant asthma, including COPD, chronic bronchitis, cough induced by gastroesophageal reflux, recurrentrespiratorytractinfections (RRTI), classic asthma, posterior nasal drip syndrome (PNDS), endobronchial tuberculosis, and angiotensin-converting enzyme inhibitor-induced cough, which are common causes of chronic cough and need to be carefully excluded in the diagnosis of cough variant asthma. In addition, chronic cardiac insufficiency, esophageal hiatal hernia, hypertensive disorders, airway inflammation, masses, foreign bodies, and smoke irritation and anxiety can all contribute to chronic cough.
Complications
Many diseases are associated with cough symptoms and need to be differentiated from cough variant asthma including COPD, chronic bronchitis, cough induced by gastroesophageal reflux, recurrentrespiratorytractinfections (RRTI), classic asthma, posterior nasal drip syndrome (PNDS), endobronchial tuberculosis, and angiotensin-converting enzyme inhibitor-induced cough, which are common causes of chronic cough and need to be carefully excluded in the diagnosis of cough variant asthma. In addition, chronic cardiac insufficiency, esophageal hiatal hernia, hypertension, airway inflammation, masses, foreign bodies, as well as smoke irritation and anxiety can all contribute to chronic cough.
Treatment modalities
Although cough variant asthma is not usually life-threatening, it should be diagnosed early and treated aggressively because it can develop into classic asthma and because the disease can seriously affect sleep, work and school.
Once cough variant asthma is diagnosed, the application of antibiotics or antiviral drugs should be stopped and care should be taken to avoid allergen exposure. In particular, primary prevention of asthma in pediatric cough variant asthma is implemented with the aim of promoting and enhancing the cellular response of Th1.
The principles of cough variant asthma treatment, like typical asthma, are mainly based on anti-inflammatory treatment with inhaled glucocorticoids. The specific treatment regimen and the dose of inhaled glucocorticoids can be found in the detailed treatment protocol in the extended reading. Continuous inhalation for 5-7 days is usually required, and the cough symptoms can gradually decrease or disappear after the airway inflammation is controlled. Inhaled glucocorticosteroids should be continued for at least 3 months to avoid recurrence. If the cough is severe, the application of bronchodilators such as inhaled or oral β2 receptor stimulants or/and oral theophyllines can temporarily relieve cough symptoms if necessary. Anti-allergic drugs such as levocetirizine, desloratadine and mast cell stabilizers such as Nedocromil and sodium cromoglycate can also be effective, but often require continuous application for more than 2 weeks.
Patients who have recurrent episodes after stopping medication should be promptly identified for allergens, effective preventive measures should be taken, and allergen vaccine treatment should be given if necessary.