Definition of Chronic Cough
A cough is a forceful ‘push’ of exhaled air that is either done voluntarily or as a reflex action (involuntary). A chronic cough is usually considered to be any cough that is persisting for more than 3 months. It may be constant, where the patient coughs every few minutes or it can be episodic, where a patient goes into a bout of coughing and it then subsides. A chronic cough is usually persistent because the cause of the cough may be a chronic disorder or the patient is constantly exposed to the same factors that may trigger the cough.
Types of Cough
Broadly, a cough can be divided into :
- Dry cough, non productive cough, in which no mucus is produced or coughed up.
- Wet cough, or a productive cough, is when mucus is present, either heard in the lungs or airways (chest) or coughed up into the throat or mouth.
Causes of a Persistent Cough
Chronic bronchitis is the most common cause of a persistent cough and is usually due to physical or mechanical causes rather than an infection. In contrast, acute bronchitis is often a result of an upper respiratory tract infection.
A cough associated with chronic bronchitis is commonly known as a ‘smoker’s cough‘ due to the prevalence of this condition in tobacco smokers. Smoking leads to chronic obstructive bronchitis, a type of chronic obstructive pulmonary disease (COPD), which results in a loss of elasticity of the lungs, swelling of the airways with mucus production and destruction of the air sacs in the lungs. Frequent clearing of the throat, shortness of breath (dyspnea) and difficulty in breathing, especially while asleep, are the most common symptoms that accompany the persistent wet cough in chronic bronchitis.
Post-Respiratory Tract Infection Cough
This cough usually persists for a few weeks to months after a respiratory tract infection or generalized infection that involves the respiratory tract, like the seasonal flu (influenza). It is more common after a viral respiratory tract infection and usually the cough is dry or non-productive.
Hay fever & Post-Nasal Drip
The primary cause of these conditions is an allergic reaction and the typical symptoms of an allergy may be present. Sneezing upon waking in the morning, red itchy eyes (especially after dusk), nasal congestion and sensitivity to environmental, physical and sometimes ingested (food) factors indicates the presence of an allergy affecting the upper respiratory tract. The cough in post nasal drip is usually dry and a result of mucus ‘tickling’ the back of the throat. In contrast, a cough is not common in hay fever where the mucus is expelled through the nose (‘runny nose’). If the mucus in post nasal drip enters the lower airways and settles in the lungs, the cough may be productive or wet.
Asthmatics may cough in response to sudden exposure to certain trigger factors like exercise, inhaled (airborne) allergens, ingested (food and drink) allergens, environmental factors (typically severe cold), upon waking from sleep, and stress. If exposure to the trigger factor persists, wheezing may become evident when coughing, giving a slightly high-pitched tone to the cough with shortness of breath.
A chronic cough may develop in gastroesohpageal reflux disease (GERD) and is prominent in the morning, after waking, due to the irritation of the pharynx (back of the throat) by gastric contents (partially digested food and acid) while asleep. A cough may also occur in GERD during or after an episode of reflux ‘heartburn’. Other gastrointestinal conditions that may cause aspiration (food or liquids entering the lung from the esophagus) may also cause a cough.
Long term infections like TB (tuberculosis) and fungal respiratory infections, like Pneumocystic carinii pneumonia, may cause a chronic cough. This is more common in immunocompromised patients, like HIV/AIDS, and may be accompanied by other symptoms like night sweats, coughing up blood (hemoptysis), fever, weight loss and generalized lymphadenopathy (enlarged lymph nodes throughout the body). Pertussis, or whooping cough, is another infectious cause of a chronic cough and is more commonly seen in children. Infectious causes of a chronic cough typically causes a wet cough.
Certain medication, like ACE inhibitors, which is used in cardiovascular conditions, especially hypertension, is known to cause a chronic cough. This is usually a side effect of the drug and subsides upon discontinuing the medication.
Cardiac failure may be a slow progressing condition that causes pleural effusion (‘water in the lungs’) and this results in shortness of breath (dyspnea), a dry cough with the sound of bubbling in the lungs when breathing (crepitations).
This is a rare cause of a chronic cough and presents with many of the signs and symptoms evident in an infection.
Rare causes of a chronic cough include tonsil stones, chronic tonsillitis and an enlarged thyroid gland (goiter) where the constant sensation of an object in the throat (globus sensation) may result in a persistent cough. Cystic fibrosis and psychogenic causes are rare causes of chronic cough and may be more often seen in children.
Diagnostic Investigation of a Chronic Cough
A chest x-ray is the most common diagnostic tool used when investigating a chronic cough. Coupled with the patient’s medical history, signs and symptoms as well as clinical findings during the physical examination by a doctor, the cause of the chronic cough may be isolated. Additional investigations like allergy testing (asthma, post nasal drip), bronchoscopy and endoscopy (gastrointestinal causes) and sputum testing (TB, fungal infections, pertussis) may be necessary to diagnose the cause of a chronic cough.