Chronic cough is long-term coughing, sometimes defined as more than several weeks or months. Generally a cough lasting for more than eight weeks for an adult would meet the clinical definition of a chronic cough;[1][2][3][4][5] and for children this threshold is lower (some studies suggest that a chronic cough must persist upwards of three months).[6] The term can be used to describe the different causes related to coughing, the three main ones being[dubious ] upper airway cough syndrome, asthma and gastroesophageal reflux disease. It occurs in the upper airway of the respiratory system. Generally, a cough lasts around one to two weeks; however, chronic cough can persist for an extended period of time defined as six weeks or longer. People with chronic cough often experience more than one cause present. Due to the nature of the syndrome, the treatments used are similar; however, there are a subsequent number of treatments available, and the clinical management of the patients remains a challenge.[7] Risk factors include exposure to cigarette smoke, and exposure to pollution, especially particulates.
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.[8] Most patients with chronic cough have hypersensitivity of the cough reflex,[9] such as the Arnold's nerve reflex.[10]
Long-term coughing and constant irritation of the upper airway can be problematic for individuals who have chronic cough. Due to the consistent coughing, this can interfere with an individual's daily life. This interference can thus cause additional problems such as affecting a person's ability to ensure a consistent sleep, daytime fatigue, difficulty concentrating at work or school, headache, and dizziness. Other more severe but rare complications include fainting, urinary incontinence, and broken ribs, caused by excessive coughing.[11]
Possible causes, alone or in conjunction, that produce the chronic cough include the following.
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Further information: Particulates and Air pollution |
Developing a chronic cough can occur from different lifestyle choices. These include smoking cigarettes that the individual smokes themselves or breathes from second-hand exposure.[15] 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 polluted air.[12] Individuals who work in factories or laboratories that deal with chemicals have a chance of developing chronic cough from long-term exposure.[15]
Coughing is a mechanism of the body that is essential to the 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. With the body components involved, sensory receptors are also used.[14][15] 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 stimulus is then interpreted.[14][15] 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 together create the reflex known as coughing.[8]
There are three main types of chronic cough.[dubious ]
Typical evaluation of chronic cough begins with diagnosing the person's lifestyle choices, such as smoking, environmental exposure or medication. From this doctors can opt to use chest radiography if the patient does not smoke, takes any angiotensin-converting enzyme inhibitor, or still has a persistent cough after the period of medication.[13][11]
A prolonged cough such as one that falls under the chronic cough syndrome can become a medical emergency. Concerning symptoms are a high fever, coughing of blood, chest pain, difficulty of breathing, appetite loss, excess mucus being coughed, fatigue, night sweats, and unexplained weight loss.[11][15]
By diagnosing which type of cough is present, individuals may further identify the cause of the chronic cough. These coughing types include the following. A dry cough is a persistent cough where no mucus is present; this can be a sign of an infection. A chronic wet cough is a cough where excess mucus is present; depending on the colour of the phlegm, bacterial infections may be present.[11] A stress cough is when the airways of the throat are blocked to the point that it causes a reflexive spasm. A whooping cough is when a ‘whooping’ sound is present; this is a normally an indication of infection.[14]
There is insufficient evidence to determine if the following approaches are beneficial for treating chronic cough: Treating childhood obstructive sleep apnoea,[22] modifying the indoor air quality,[23] or treatment with inhaled chromones.[24]
The prevalence of chronic cough in many communities in Europe and the U.S. is 9–33% of the population. Chronic cough is three times more common in those who smoke compared to people who never smoke.[25] The most important risk factors for chronic cough are tobacco smoking and working in a dusty job.[26] Exposure to tobacco smoke in a home environment is also a risk factor for children due to second-hand smoke inhalation.[25] Other causes of chronic cough include higher particulate matter concentrations in air, related to increase cough and sore throat in children. An increase in nitrogen dioxide has also shown a rising association with chronic cough syndrome.[25]
A cough that is four weeks or longer in duration is considered chronic for children.[27] Most common causes for children include asthma, respiratory tract infections and GERD. An estimation of between one and 21% of children suffer from chronic cough.[1][28][29] Causes typically diagnosed include viral bronchitis, post-infectious cough, cough-variant asthma, upper airway cough syndrome, psychogenic cough and GERD.[14][15] Due to some diagnostic methods being invasive, typically children are not suitable for such diagnosis under the age of 15. However, the bare minimum tests include chest radiography and spirometry.[8]