Cough is one of the most common reason for seeking medical attention at both the primary health centre as well as lung specialist clinic. It forms as much as one third of the cases seen at the lung specialist clinic.
Cough is an important mechanism to clear secretion and foreign material from the airway. However, it is also a means of spreading infection. Chronic cough is troublesome. It is often the complications of a protracted cough that lead people to seek medical advice at the specialist lung clinic. Examples of these are insomnia, musculoskeletal pain, urinary incontinence and hoarseness.
Coughing involves a complex reflex arc, starting with stimulation of receptors and the impulses will be integrated into a coordinated cough response in the brain which is then transmitted to the muscles involved in breathing via the nerves. The cough receptors are found not only in the distal airway but also in the upper airway such as the pharynx, paranasal sinus, as well as eardrums, pleura, diaphragm, stomach and pericardium. This explains why cough can result from conditions affecting the lung and other organs.
Cough can be defined as acute or chronic cough based on its duration. In general, acute cough is 3 weeks or less in duration while chronic cough is at least 3 weeks. Both are not mutually exclusive as acute cough may last more than 3 weeks.
Acute cough is most frequently due to the common cold, followed by acute bacterial sinusitis, exacerbation of COPD, allergic rhinitis and asthma; less commonly acute cough can be associated with serious conditions like pneumonia and heart failure.
Chronic cough can be due to a single cause or simultaneously due to two or more conditions. The most common causes of chronic cough among non-smokers are postnasal drip syndrome, asthma and gastroesophageal reflux disease (GERD). Smokers frequently have a chronic cough due to chronic bronchitis but often do not seek medical attention because they are expected to cough as a result of smoking. The less common causes are as listed:
• ACEI inhibitor-induced cough
• Occult left heart failure
• Lung cancer
• Infection like tuberculosis
• Interstitial lung disease
• Disorders of the external ear canals
• Disorder of the diaphragm
• Disorders of the pleura or pericardium
• Disorders of the oesophagus or stomach
• Nasal polys
• Uvular or tonsillar enlargement
• Thyroid disorder
• Psychogenic cough
A study on 102 patients with chronic cough by Irwin in 1990 showed that causes of cough were determined in 99% of the cases. Cough was due to a single condition in 73% and multiple conditions in 26% of the time and 3 concurrently existing conditions in 3%. The study also showed that postnasal drip syndrome was the single most common cause (41%) followed by asthma (24%) and GERD (21%)
Postnasal Drip Syndrome
Postnasal drip syndrome is the most frequent cause of both acute and chronic cough. Postnasal drip syndrome plus one or two other conditions such as GERD are often involved in chronic cough.
In addition to cough, complaints associated with postnasal drip syndrome are:
1. A feeling of something dripping into throat
2. A need to constantly clear the throat
3. Nasal congestion or discharge
The person with postnasal drip syndrome usually has a recent cold, or suffers from allergic rhinitis, acute or chronic sinusitis. Treatment of cough due to postnasal drip syndrome is determined by the diagnosis of the underlying conditions.
Asthma is a common cause of chronic cough in both children and adults. It must be considered in all patients with chronic cough. Asthma is a chronic inflammatory disease of the airway presenting with characteristic symptoms of chest tightness, wheezing, shortness of breath and cough. It is associated with physiological abnormalities of variable airflow obstruction and airway hyper-responsiveness.
All asthmatics experience cough as a symptom but when cough is the only asthma symptom, the disease is called cough variant asthma. The diagnosis is suggested by the presence of airway hyper-responsiveness. The treatment of cough variant asthma should be the same as for asthma presenting with other symptoms.
Gastroesophageal Reflux Disease (GERD)
GERD is caused when contents from the stomach reflux into the oesophagus. GERD is a common cause of chronic cough. The reflux is caused by transient relaxation of the lower oesophageal sphincter.
GERD is often difficult to diagnose. More than half of the persons with chronic cough due to GERD are unaware of reflux, they do not complain of typical symptoms such as heartburn, sour taste or regurgitation. Test to detect GERD may include 24-hour monitoring of acidity in the oesophagus with a catheter, barium swallow and gastroscope.
GERD is sometimes one of the ‘other’ causes of chronic cough when chronic cough is due to more than one cause. GERD and cough also can have self-perpetuating cycle in conjunction with another cause of cough. Cough due to another cause perpetuates reflux from the stomach, which in turn causes cough due to GERD, so that the patient ends up with two causes of chronic cough.
Treatment of GERD includes lifestyle changes, dietary control and medication.
Maintain a healthy body weight, lose weight if one is overweight.
Avoid large meals, eat small frequent meals.
Eat slowly and chewing your food well.
Do not lie down within 3 hours after eating.
Also avoid physical exercises right after eating.
Avoid tight clothing and belts.
Sip small amounts of fluids during meal. Instead drink more fluid between mealtimes.
Sleep with your head of bed elevated or on 2 or more pillows.
Dietary Controls with avoidance of certain food and drinks
Drinks with caffeine like coffee, tea, chocolate, milo
Strong flavoured food like peppers, peppermint, onions, garlic
High fat food like nuts, milk, butter, cream, fried food, cookies, cakes
Citrus fruits and juices like oranges, lemon, grapefruit
Proton-pump inhibitor such as Omeprazole, Nexium.
Chronic bronchitis is a frequent cause of chronic cough in the community, especially in the smokers. However, they do not frequently present for medical attention because they are ‘expected to cough’. Tobacco smoke causes the airway inflammation, excessive mucus secretion and impairment of normal clearance of mucus. Effective cough is important for it helps to clear excessive mucus from the airway. Smoking cessation is the only fully effective treatment. An inhaler with anti-inflammatory and bronchodilator effects may decrease sputum production and cough. Antibiotics may be necessary in the presence of infection.
Bronchiectasis is not a frequent cause of chronic cough because its incidence is decreasing. Cough is a cardinal symptom of bronchiectasis. Bronchiectasis is a lung disease in which the bronchial tree is dilated and chronically colonized by bacteria. Clinical history, chest x-ray and CT scan of the lung usually make the diagnosis. Effective cough is important for this condition. Chest physiotherapy and drugs to stimulate clearance of mucus are accompanied by intermittent course of antibiotics to keep infection in check.
Post Infectious Cough
Cough that persists for 3 or more weeks as the only symptom after a viral upper respiratory tract infection may be a postinfectious cough. This cough is due to persisting inflammation after infection and will usually go away in time, but treatment with a course of steroid or inhaler will hasten the recovery. Post infectious cough is more significant if there was a contact with a known case of pertussis, also known as whooping cough. In this case, antibiotic treatment should be given.
Lung cancer should be considered a potential cause of chronic cough in all patients especially in present or prior smokers or persons with occupational exposure to carcinogens.
Cough frequently occurs as a symptom at some time during the course of lung cancer. Cough as a presenting symptom may be ignored by smokers because of the expectation of cough as a side effect of smoking. Chest x-ray, CT Scan thorax, percutaneous lung biopsy and bronchoscopy are some important diagnostic tests when lung cancer is suspected.
Tuberculosis of the lung should be considered as a cause of chronic cough as the incidence in Singapore is still high. This is especially so if there are other accompanying complaints like fever, night sweats, loss of appetite and weight. The patient is at risk if there is a history of exposure or if there are other risk factors like diabetes mellitus, underlying malignancy or immunocompromised state. The diagnosis is confirmed by typical x-ray changes and sputum tests. Sometimes biopsy may be needed if it presents like a mass in the lung or if it is a pleural effusion. The disease is treated with 3 or 4 types of medicine for 6 or 9 months depending on the treatment regimen.
ACE Inhibitor induced Cough
Angiotensin converting enzyme (ACE) inhibitors are blood pressure lowering drugs that can cause chronic cough as a side effect in about 10% of persons who take the drugs. The cough is typically dry and hacking. Discontinuance of the drug causes the cough to improve or resolve within a month.
Habit or nervous cough is a throat clearing noise made by a person when he is nervous and self-conscious. Medical treatment is not necessary.
Psychogenic cough has no apparent cause. Emotional and psychological problems are likely causes. However other illnesses must be ruled out before a firm diagnosis is made. Suggestion therapy, psychological counselling or psychiatric intervention is appropriate.
The Lung Specialist Clinic uses a systematic diagnostic approach in evaluating both acute and chronic cough. A full medical examination and laboratory or radiological tests may be necessary. In the great majority of cases, the specific cause of cough can be diagnosed and successfully treated with therapy specific to the cause.