Coughing is the way that our lungs clean themselves of inhaled dust and debris. Occasional coughing is a normal and necessary way that our lungs "clean" themselves. Coughing can also be brought on by infections such as bronchitis, pneumonia, influenza, or even the common cold. In most cases, cough due to one of these illnesses is self-limited and goes away after one to two weeks. Coughing that lasts longer than this is usually due to another cause.
A new cough that fails to improve in one to two weeks in a smoker can be an early sign of lung cancer and should be evaluated by a physician, usually with a chest x-ray.
In nonsmokers, a lasting cough is most likely due to one of five lung diseases: asthma, gastroesophageal reflux, post nasal drip, medication side effects, or vocal cord dysfunction.
Asthma most commonly presents with shortness of breath and wheezing but there are some patients with asthma whose main symptom will be cough. These patients with so called "cough-variant asthma" sometimes notice that their cough is worse after exercise, exposure to cold air, or exposure to different allergens. Cough-variant asthma can often go undiagnosed because the basic test to diagnose asthma, spirometry, is often normal when patients are in their physician's office. Cough-variant asthma can be diagnosed by the use of a methacholine challenge test which can amplify abnormalities on spirometry thus allowing the physician to uncover signs of asthma. Cough-variant asthma is usually a milder form of asthma and responds very well to traditional asthma medications.
Gastroesophageal reflux is a very common cause of cough and clues to its presence may include cough after eating, cough when laying flat (for example, when going to bed), and cough when waking up in the morning. Many patients do not know that they have gastroesophageal reflux and lack heartburn which is another common symptom of gastroesophageal reflux. Gastroesophageal reflux can be diagnosed by a test called a 24-hour pH probe, endoscopy, or by improvement in the cough with a trial of antireflux medications.
Post nasal drip is one of the most common causes of persistent cough and clues to its presence can include frequent blowing of the nose, nasal "stuffiness", or sinusitis. Sinusitis can be diagnosed by either sinus x-rays or a sinus CT scan. Although sinus x-rays are relative simple to obtain, the CT scan provides more clear images of the sinuses and is often necessary for accurate diagnosis. Post nasal drip can be treated with antihistamines, decongestants, or nasal drying agents. There are three forms of antihistamines currently available: the first generation antihistamines are available over the counter but can cause drowsiness; the second generation antihistamines are available by prescription and are more expensive but are less likely to cause drowsiness; inhaled antihistamines generally avoid the side effects of oral antihistamines and can be useful in some patients. Decongestants can be taken to help dry the nasal passages but can occasionally cause jitteriness and tend to be less effective if there is an allergic component to the post nasal drip. Nasal drying agents (such as inhaled Atrovent) can be used directly in the nose to help reduce nasal secretions; the effect of over the counter nasal drying agents (such as Neo-Synephrine) tends to wear off after a few days and people can build up tolerance to them whereas the prescription medications (such as Atrovent) are not associated with tolerance and their effect does not diminish over time.
Medications which can commonly cause cough include angiotensin converting enzyme inhibitors (ACE inhibitors) which are used to treat high blood pressure or heart failure. Some of the common ACE inhibitors include Zestril, Capoten, and Vasotec. Often the cough associated with these drugs develops many months after starting their use. The cough associated with these drugs usually goes away within two weeks of stopping them. There are other medications which can sometimes cause cough by triggering asthma (such as beta blockers or aspirin) and you should always give your physician a complete list of both prescribed and over the counter medications that you use in order to help him/her to determine if your cough may be brought on by one of them.
Vocal cord dysfunction is a common and frequently overlooked cause of cough. It can be very difficult to recognize and requires a test called a videolaryngostroboscopy for accurate diagnosis. There are some clues that can occasionally help identify vocal cord dysfunction such as the presence of hoarseness, cough that occurs during speech, or when talking on the phone, or a history of vocal cord abuse (such as singing or loud shouting). Many times, vocal cord dysfunction can be brought on by another condition which irritates the vocal cords (such as asthma or gastroesophageal reflux).
For many patients, the cough will have more than one cause. This can be especially frustrating for both the patient and the physician since the elimination of the cough will require identification of all of the causes and treatment of all of the causes before the cough will go away.
The evaluation of persistent cough starts with a thorough history and physical examination. Frequently, clues to the cause of the cough can be identified and treatment started during the first office visit. For more difficult cases, additional testing is necessary. Often, your physician will start with a trial of medications before moving to expensive or invasive tests. Because the most common cause of cough is post nasal drip, an initial trial of antihistamines and/or decongestants is frequently the first step. If the cause of cough is not strongly suspected based on the history and physical examination alone, a chest x-ray is done in most patients at least once during the evaluation of cough to ensure that there are no structural abnormalities in the lung which might be causing the cough. Unusual causes of cough can include benign tumors of the lung, bronchiectasis, "habit" cough, foreign body in the lung, and interstitial lung disease.
The treatment of cough depends on its cause and treatment of this will ultimately guide the most effective therapy. Cough suppressants can reduce coughing but do not treat the underlying cause of cough and should not be a substitute for thorough medical evaluation. At The Ohio State University Pulmonary Clinics, we often recommend patients start with an over the counter cough suppressant containing dextromethorphan. Prescription cough suppressants can be tried in patients who fail over the counter medications but generally these medications are only slightly more effective than the nonprescription formulations.
Persistent cough in nonsmokers rarely is a sign of serious underlying disease and is more often a nuisance rather than a life threatening ailment. Nevertheless, it can impair one's work, recreational activities, and social activities. With proper evaluation and diagnosis, the persistent cough can generally be substantially reduced or eliminated completely.