Q: What causes chronic cough and how is it treated?

A: First, let’s define cough. Cough is a normal physiological response to an irritation of the body’s cough receptors in the upper and lower respiratory tracts, the esophagus, and around the heart. It is an important mechanism to clear mucus from the respiratory tract. Cough can also be a very burdensome symptom that accounts for millions of medical visits in the U.S. each year.

Doctors separate cough into three categories based on duration:

  • Acute cough — three weeks or less.

  • Subacute cough — three to eight weeks.

  • Chronic cough — eight weeks or more.

Acute cough is most commonly the result of a viral upper respiratory infection. Subacute cough can be caused by infection such as pertussis (also known as whooping cough), medications, smoking, and environmental exposures. The first step in treating subacute cough is to stop the medication, stop smoking, or avoid the environmental exposure.

Chronic cough tends to create a significant burden on the patient’s quality of life. It can be caused by many diseases but the vast majority of cases are caused by one of the following three diseases:

  • Asthma.

  • Upper airway cough syndrome — due to post nasal drip.

  • Gastroesophageal reflux disease (GERD)

Typically, a doctor will determine which of these diseases is the most likely culprit for the patient’s cough based on history, physical exam, and laboratory or imaging data. Once that determination is made, a treatment trial is recommended to assess the patient’s response. For asthma, patients are often prescribed at least four weeks of regular use of a corticosteroid-containing inhaler. For GERD, patients undergo a two-month trial of proton pump inhibitor therapy to suppress acid in the stomach. For upper airway cough syndrome, the combination of antihistamine medications and intranasal steroid sprays are most commonly used for at least two to four weeks.

If cough persists despite these treatment trials, it may be a symptom of chronic lung disease or sign of a slow growing infection. Some of these less common causes of chronic cough include:

  • Lung cancer.

  • Chronic bronchitis — a type of chronic obstructive pulmonary disease (COPD).

  • Bronchiectasis — dilation of the airways sometimes due to recurrent infection.

  • Side effect of blood pressure medicines called ACE inhibitor.

If this is the case, a doctor will likely refer the patient to a cough center for lung function testing, allergy testing, or advanced imaging such as a CT scan. An ear, nose and throat (ENT) or gastroenterologist (GI) specialist may be consulted to assist with additional workup.

Despite a thorough evaluation, the underlying cause of chronic cough may not be identified or may not respond to initial therapy in some cases. This is referred to as refractory chronic cough or unexplained chronic cough. These patients may have cough for years and should be referred to a cough specialist whenever possible for additional treatment options, clinical trials and advanced workup.

If you experience a cough that lasts beyond eight weeks, talk to your doctor. Every effort should be made to establish a diagnosis for the underlying cause of the cough. Treating the underlying cause of cough is always preferred to simply treating the symptom.

Sean P. Duffy is a pulmonologist at Temple Lung Center and an associate professor of clinical thoracic medicine and surgery at the Lewis Katz School of Medicine at Temple University.