Causes of Chronic Cough
Most diagnostic workups for the cause of a cough differentiate between chronic cough in nonsmokers with a normal chest x-ray (CXR) and chronic cough in smokers with or without an abnormal CXR. The most common causes for chronic cough in a nonsmoker with a normal CXR are postnasal drip syndrome, asthma, and gastroesophageal reflux disease (GERD). Medications called ACE inhibitors are another major cause of chronic cough.
Common causes for chronic cough in smokers are bronchitis and lung cancer. Even though a chronic cough in a nonsmoker usually does not indicate problems as serious as these, it should be evaluated by a physician to exclude rare but serious causes.
Less common causes include: congestive heart failure, disorders of the upper airways, disorders of the pericardium, bronchogenic carcinoma, interstitial lung disease, chronic pulmonary infection (e.g., tuberculosis), cystic fibrosis, and psychogenic disorders.
Postnasal Drip Syndrome and Chronic Cough
Postnasal drip syndrome is suggested by frequent nasal discharge, sensation of drainage in the back of the throat, and frequent throat clearing. The syndrome is noted on physical examination by the rough appearance, termed cobblestoning, of the back of the throat. Sinus x-rays or sinus CT (computed tomography) scan may show evidence of sinusitis. Causes of postnasal drip include sinusitis, allergic rhinitis, and vasomotor rhinitis. Postnasal drip syndrome is the most common cause of chronic cough.
Chronic cough due to postnasal drip is generally treated with decongestants and antihistamines, with or without nasal steroid sprays. Treatment may also include a vasoconstrictor such as oxymetalazone, which should not be used for more than 5 days. Chronic cough due to postnasal drip may take a few weeks to a couple of months to resolve. Underlying sinusitis is treated with antibiotics.
Asthma and Chronic Cough
Asthma that is asymptomatic except for cough is called cough-variant asthma. This condition is difficult to diagnose because the physical examination and pulmonary function test results can be normal. The diagnosis may be suggested by caused by cold air, fumes, fragrances, or exercise.
Coughing that starts after the initiation of a beta-blocker also suggests asthma. Beta-blockers are medications commonly used to treat high blood pressure, heart disease, migraines, palpitations, and other conditions. Beta-blockers are also used in eye drops for glaucoma and other eye problems. Beta-blocker eye drops can precipitate asthma symptoms, including cough. Confirmation of the diagnosis of cough-variant asthma may include a breathing test called a methacholine bronchial challenge test.
Gastroesophageal Reflux Disease (GERD) and Chronic Cough
GERD is the third most common cause of chronic cough. The diagnosis may be obtained from the medical history alone. Patients often present with classic symptoms of frequent heartburn or sour taste in the mouth. If these symptoms are present, therapy directed at GERD is initiated to resolve the cough.
Forty percent of patients with GERD do not present with the classic symptoms. These patients may complain only of cough. In this case, a 24-hour esophageal pH probe—a small plastic catheter inserted through the nose and placed into the esophagus, above the stomach—may be performed to measure the pH (acid concentration) in the esophagus. If the pH in the esophagus falls below a certain level, acid is refluxing from the stomach.
Alternatively, therapy directed at reflux can be given as a diagnostic test. If the cough resolves with GERD therapy, the cough is attributed to GERD. This is reconfirmed if the cough returns with discontinuance of therapy.
The treatment for GERD includes elevation of the head of the bed; not eating or drinking 2 to 3 hours before bedtime; and avoiding certain foods, such as fatty foods, chocolate, alcohol, orange juice, and caffeine. Medications directed at reducing acid production in the stomach, such as proton pump inhibitors, are used as well.
ACE Inhibitors and Chronic Cough
ACE inhibitors can be excluded as the cause of chronic cough by discontinuing their use. The cough typically resolves in 1 to 4 days but can take up to 4 weeks. Therefore, eliminating the drug for a couple of days is not sufficient to exclude an ACE inhibitor as the cause. Further confirmation is made by the return of cough on resumption of the medication.
Other classes of medication need to be used if the cough is due to an ACE inhibitor.
Bronchiectasis and Chronic Cough
Bronchiectasis (chronic dilation of the bronchi or bronchioles resulting from inflammatory disease or obstruction) can be diagnosed by high resolution CT scan that shows the dilated airways. Once this diagnosis is established, the cause should be determined and, if possible, therapy initiated.
Chronic Bronchitis and Chronic Cough
The diagnosis of chronic bronchitis is obtained from a history of smoking and the production of sputum with the cough most days of the week, for 3 months, in 2 successive years. Chest x-rays are obtained to exclude other pathology. In a smoker, any change in a chronic cough and any new cough warrant further evaluation.
Smoking cessation can resolve the cough associated with chronic bronchitis. Bronchodilators can help the cough as well.
Lung Cancer and Chronic Cough
Lung cancer is the cause of a chronic cough in less than 5 percent of patients with a normal CXR. It is suspected as a cause of chronic cough most often when there is an abnormal CXR and a history of smoking. Abnormal CXR dictates that a biopsy be performed to obtain a sample of the abnormal tissue for analysis. When the CXR is normal and lung cancer is suspected, a CT scan of the chest may be obtained. Bronchoscopy is often the next diagnostic test in patients with normal radiographic studies.
Foreign Body and Chronic Cough
When a foreign body is suspected as the cause of chronic cough, fiberoptic bronchoscopy is usually performed.
Nonspecific Therapy for Chronic Cough
Nonspecific therapy for cough may be employed to relieve symptoms until the therapy directed at the cause becomes effective. The most commonly used cough suppressant is dextromethorphan. Dextromethorphan is chemically related to morphine but has no narcotic effect. Adverse effects, occuring in fewer than 1 percent of people, include drowsiness, dizziness, nausea, constipation, and abdominal discomfort.
Dextromethorphan is contraindicated in a person taking a monoamine oxidase inhibitor (MAOI). Overdosage can occur and can lead to coma and respiratory depression. Codeine is another effective cough suppressant and may cause side effects similar to dextromethorphan, but with increased frequency. Dependency with prolonged use can occur with codeine.