Chronic cough

Common symptoms present in chronic cough include a runny or stuffy nose, a feeling of liquid running down the back of the throat (postnasal drip), frequent throat clearing (coughing) and sore throat, hoarseness, wheezing or shortness of breath, heartburn or sour taste in a person's mouth, and in rare cases coughing blood.[1]

Possible causes alone or in conjunction can cause the chronic cough which include:

• Postnasal drip, when excess mucus is produced in the sinus of the nose and drips back towards the throat, causing a cough reflex also known as upper airway cough syndrome. Postnasal drip can be caused by direct irritation of the post nasal drip or an inflammation of cough receptors in the upper airway. 34% of postnasal drip cases contribute to the cause of chronic cough.[3]
• Asthma that affects the upper respiratory tract. Other causes such as cold air or chemicals breathed in can also induce coughing.[4]
• Gastroesophageal reflux disease (GERD), a common condition where the backflow of stomach acid between the throat and the stomach causes an irritation that can lead to chronic cough.[5]
• Infections such as symptoms of pneumonia, flu, cold, or other infections in the upper respiratory tract include coughing that can persists even after the infection has subsided. It is commonly mistaken as a symptom of the infection can be chronic cough, known as whooping cough.[4]
• Blood pressure drugs such as angiotensin-converting enzyme, which is commonly prescribed to individuals with high blood pressure and cardiac failure and are known to have a side effect of chronic cough.[2]
• Chronic bronchitis, an inflammation in the major airways such as the bronchial tubules that causes the coughing of coloured sputum. Most carriers of chronic bronchitis have a history of smoking. Due to the nature of chronic bronchitis, it is on a spectrum of smoking-related lung disease also known as chronic obstructive pulmonary disease. Because of this spectrum, other lung diseases on the spectrum such as emphysema can co-exist with COPD. It accounts for 5% of chronic cough.[2]
• Chemical irritants such as cigarette smoke or other irritants are a common factor that can lead to chronic cough. These irritants typically contribute towards chronic bronchitis.[2]
• Other notable rare causes include: aspiration, bronchiectasis, bronchiolitis, cystic fibrosis, laryngopharyngeal reflux, lung cancer, non-asthmatic eosinophilic bronchitis, sarcoidosis.

Developing a chronic cough can occur from different life style choices. These include smoking cigarettes that the individual smokes themselves or breathes from second-hand exposure.[6] Long-term exposure to smoke can irritate airways and lead to chronic cough and in severe cases lung damage. Other risk-factors include exposure to the air.[3] Individuals that work in factories or laboratories that deal with chemicals have a chance of developing chronic cough from long term exposure.[6]

Coughing is a mechanism of the body that is essential to normal physiological function of clearing the throat which involves a reflex of the afferent sensory limb, central processing centre of the brain and the efferent limb. In conjunction to the components of the body that are involved, sensory receptors are also used.[5][6] These receptors include rapidly adapting receptors which respond to mechanical stimuli, slowly adapting receptors and nociceptors which respond to chemical stimuli such as hormones in the body. To start the reflex, the afferent impulses are transmitted to the medulla of the brain this involves the stimulus which is then interpreted.[5][6] The efferent impulses are then triggered by the medulla causing the signal to travel down the larynx and bronchial tree. This then triggers a cascade of events that involve the intercostal muscles, abdominal wall, diaphragm and pelvic floor which in conjunction together create the reflex known as coughing.[1]

There are 3 main types of chronic cough which are the following:

• Upper airway cough syndrome is the most common cause of chronic coughing. It is diagnosed when the secretion of excess mucus from the nose / sinus drains into the pharynx or the back of the throat causing an induced cough.[3]
• Asthma is the main way to identify the chronic cough as a cause from asthma is that the airflow is obstructed when coughing causes a shortness of breath, wheezing, dyspnea and coughing.[4]
• Gastroesophageal reflux disease (GERD) is identified with 2 mechanisms which are the distal esophageal acid stimulating the esophageal-treachebronchial cough reflex due to the vagus nerve and the microbial esophageal contents of the pharynx and tracheobronchial causing a cough reflex.[5]

• Upper airway cough syndrome treatments include avoiding environmental irritants (chemicals) and offending antigens. This involves treating the sinus with antibiotics to stop nasal drip. Individuals should avoid decongestants found in off the shelf pharmacies to allow rhinitis medicamentosa to work. In severe cases where the cause is not clear, patients should use empiric therapy which is a combination of antihistamine and decongestants. Results typically show within 2 weeks of therapy but can take up to several months for results to show. Absence of standard clinical procedure that test for rhinorrhoea and excess sputum production should not preclude an empiric trial with antihistamine decongestants as they are not effective in treating upper airway cough syndrome.[2]
• Treating children who have a non-specific chronic cough with asthma medications such as inhaled beta2-agonists (e.g., salbutamol) or inhaled corticosteroids does not improve the clinical symptoms.[7][8]
• Codeine-based cough medications are contraindicated for children under 12 years old due to the risk of respiratory suppression and the potential for opioid toxicity.[9]
• Leukotriene receptor antagonist-based medications[10] and methylxanthines[11] are not recommended for treating children with persistent non-specific cough.
• Gastroesophageal reflux disease (GERD) treatments include intense monitoring with a dual channel 24-hour pH probe for diagnosis of the severity of GERD. Other monitors such as nasopharyngoscopy can reveal glottis changes associated with the refluxes that occur. Acid suppressive medication can be taken which include histamine 2 (H2) blockers, proton pump inhibitors (PPI) and prokinetic agents. This medication tends to show results within 2 weeks however 6–8 weeks is ideal for conclusive results. Patients are to remain on treatment for up to 6 months.[5][2]
• Moderate levels of evidence suggest that the use of a clinical pathway that includes an evidence-based algorithm (flow chart) for treating children who have chronic cough may improve clinical outcomes.[12]
• There is insufficient evidence to determine if the following approaches are beneficial for treating chronic cough: Treating childhood obstructive sleep apnoea,[13] modifying the indoor air quality,[14] or treatment with inhaled cromones.[15]

The prevalence of cough in many communities in Europe and USA is 9–33% of the population. Chronic cough is more common in those who smoke by threefold compared to people who never smoke.[16] Data analysis shows that exposure to tobacco smoke in a home environment is a risk factor for children due to second hand smoke inhalation.[16] Other causes of chronic cough include higher PM10 concentrations have been related to increase cough and sore throat in children. An increase in nitrogen dioxide has also show a rising association with chronic cough syndrome.[16]

A cough that is 4 weeks or longer in duration is considered chronic for children. Most common causes for children include asthma, respiratory tract infections and GERD. Other causes typically diagnosed differently include viral bronchitis, post-infectious cough, cough-variant asthma, upper airway cough syndrome, psychogenic cough and GERD.[5][6] Due to the way of diagnosis being invasive, typically children are not suitable for diagnosis under the ages of 15. However the bare minimum tests include chest radiography and spirometry.[1]