Cough means that something is irritating the lung, airways, voice box, esophagus, or back of the throat.  When cough is sudden in onset and of short duration, it is usually caused by a recent illness such as the common cold, pneumonia, bronchitis, or laryngitis, and the diagnosis is usually obvious.  However, when the cough is of prolonged duration, the diagnoses may not be as obvious but the causes may be a lot more serious.  Hence, it is imperative to rule out serious diseases and to make specific diagnoses in all cases of chronic cough.

Chronic cough means that someone has been coughing for several weeks without showing signs of improvement, which is in contrast to the self-limited course of most new-onset cough disorders mentioned above.  The causes of chronic cough may be divided into several broad clinical categories:

Smoking is by far the commonest cause of chronic cough.  Chronic inhalation of tobacco smoke irritates the airways, causing the mucus glands to enlarge, become hyperactive, and produce large amounts of sputum.  This leads to the familiar moist cough of smokers with daily sputum expectoration, a condition medically known as chronic bronchitis.  Nonsmokers who are exposed to second-hand smoke may also develop a similar condition.  By definition, anyone who expectorates sputum on most days of the week may be given the diagnosis of chronic bronchitis.

Moreover, besides chronic bronchitis, primary or secondary smoke inhalation may also cause airway spasm, a condition similar to asthma, which can also cause chronic cough but with little or no sputum expectoration.  Although important, chest x-rays are not usually useful except in ruling out other serious causes of chronic cough such as lung cancer or tuberculosis. 

Chronic sinusitis with chronic sinus drainage, by irritating the back of the throat or by provoking micro aspirations, can cause a chronic dry cough that will not abate until the sinusitis is treated.  The diagnosis is difficult because sinus x-rays may fail to detect the condition.  A useful clinical clue is to ask the patient to point to the site where the cough is coming from.  If the patient points to the neck instead of the chest and if chronic sinusitis is clinically suspect, it may be wise to prescribe a short course of antibiotics as a diagnostic & therapeutic trial.

Allergies, common in spring and fall, may cause cough by irritating the nose, sinuses, and airways.  In such cases, history is crucial because it provides the seasonal clue.  Any seasonal cough is an allergy suspect and allergy treatments in the form of antihistamines or cortisone usually provide relief.  Reversible airway spasm is almost always present in seasonal cough giving the condition its common name of seasonal asthma.

Acid reflux—the condition where stomach acid creeps up the esophagus at night when we are lying flat—may cause cough by two mechanisms.  Cough may be due to nocturnal micro aspirations or to esophageal irritation, both of which provoke daily cough, especially at night or upon rising in the morning.  Treating reflux aggressively by elevating the head of the bed, avoiding late eating and drinking, abstaining from smoking and caffeine, and suppressing stomach acid with medicines usually provides relief within a week or two.  A therapeutic trial confirms the diagnosis better than any other available test.

Certain blood pressure medications are cough provokers such as beta blockers (eg. Inderal) and ACE inhibitors (eg. Lisinopril).  The cough may come soon after they are started or several months or even years later.  When it comes long after such treatments are begun, it may be difficult to diagnose unless the doctor keeps a high index of suspicion.  There is no test to diagnose medicinal cough except stopping the medicine, which causes the cough to resolve within a few weeks.

Chronic sub-clinical asthma is commonly associated with chronic cough and may not be obvious because of the lack of shortness of breath and wheezing.  In fact, cough may be the only symptom of sub-clinical asthma.  In such cases, testing lung function with a breathing machine shows reversible airway obstruction, which when treated with inhalers causes the cough to resolve.

Adult whooping cough is common and may cause cough spells that are so prolonged and severe that they end in vomiting.  The cough may persist for many months and responds poorly to usual treatments.  The diagnosis is made by blood tests and patience is the best approach.

Finally, the less common causes of chronic cough should be suspected when the more common causes have been ruled out. Investigations, which include x-rays, are indicated, especially when coughs get worse in spite of treatments.  No cough should be left undiagnosed.

ISSUE 91 - February 2010