(LifeWire) - An asthma diagnosis is usually based on a person's experience of wheezing, shortness of breath and cough. A certain subset of people experience only a chronic cough, making a conclusive asthma diagnosis more complicated. This condition is called cough variant asthma, or CVA for short.
A chronic cough is defined as one that lasts longer than 8 weeks. There are many causes of chronic cough in nonsmoking adults. Asthma, gastroesophageal reflux disease, post-nasal drip and post-infectious cough are the most common causes. Asthma is believed to be responsible for 24% to 29% of these persistent coughs.
Diagnosing CVA in children presents an added challenge. As many as 15% to 20% of children under 11 years of age have a chronic cough, which often resolves itself. Children with a cough and no other asthma symptoms are not helped by the use of inhalers.
These children should not only be evaluated for the presence of the main causes of chronic cough, but they also need to be checked for the inhalation of a foreign object (such as a dime or a bead) and for other diseases diagnosed in childhood, such as cystic fibrosis.
While it is unclear how common CVA is in the general population, or what percentage of asthmatics it affects, what is clear is that many people with this diagnosis wait longer than other asthmatics for their condition to be recognized.
This added delay means that along with the untreated cough, which may be uncomfortable, they also have untreated inflammation in the airways. It has been shown that the microscopic changes in the airways of patients with CVA are the same as the airways of regular asthmatics.
The diagnosis of CVA may require the following:
- Chronic cough (not due to another cause)
- Positive methacholine inhalation challenge (MIC), and
- Positive response (improvement / resolution of symptoms) with traditional asthma therapy
Most people with CVA will have normal pulmonary (lung) function tests. These tests are ordered to find the airway obstruction that asthma can cause. Because people with CVA will not show an obstruction, an MIC may be performed. The MIC test is given with the inhalation of methacholine, which irritates the airways in susceptible individuals and causes the onset of asthma symptoms.
If the MIC test is positive in someone with a chronic cough, it is likely that they have CVA. If the test is negative, they do not have CVA. However, it is not always necessary to perform this test. But it can be helpful if the diagnosis is not established by history, exam, PFTs and response to therapy.
Even if the methacholine challenge is positive, it still does not make a definitive diagnosis of asthma. The final step in actually concluding that someone has CVA is a positive response to standard asthma therapy.
Treatment includes an inhaled steroid and a bronchodilator. It is important for people with CVA to know that it may take a week for symptoms to improve, and it may take as long as months for the cough to stop entirely. Some people may be advised to use these inhalers continually, even after the cough has improved or disappeared.
According to the American College of Chest Physicians (ACCP) Consensus Panel, one issue that can arise in treating people with CVA is an increase in coughing when inhalers are used. Patients with CVA have a more sensitive cough reflex – and less airway reactivity – than other asthmatics, which explains the absence of wheezing and shortness of breath.
If using inhaled steroids is problematic, or if the cough is not responding well enough, the doctor may recommend a short course of oral steroids. Oral steroids are generally used for a week and then inhaled steroids are reintroduced. It is important to be sure that the inhalers are being used properly before deciding that inhaled treatment has failed.
The ACCP also found that addition of Zafirkulast, a leukotriene modifier, may have a role in treating CVA that has not responded entirely to steroids and a bronchodilator. Zafirkulast appears to have a role in suppressing a cough that has been inadequately treated with inhaled steroids. Zafirkulast likely inhibits inflammation in the airway cough receptors, making them less sensitive. It is unclear if leukotrienes could be used alone as first-line therapy.
In some people, there is evidence that CVA will transform into regular asthma with the onset of wheezing and shortness of breath. Some small studies have shown that as many as 36% of patients with CVA will develop other symptoms of asthma. The conversion to asthma has been associated with the length of time that the cough has persisted.
Chang, Anne B. "Cough, Cough Receptors and Asthma in Children." Pediatric
Pulmonology (1999) 28(1):59-70. 22 Jan. 2008
Dicpinigaitis, Peter V. "Chronic Cough Due to Asthma: ACCP Evidence-Based Clinical Practice Guidelines." Chest (2006) 129:75S-79S. 22 Jan. 2008 <http://www.chestjournal.org/cgi/content/full/129/1_suppl/75S>
Irwin, Richard S. and J. Mark Madison. "The Diagnosis and Treatment of Cough." New England Journal of Medicine (2000) 343(23):1715-1721. 22 Jan. 2008 <http://content.nejm.org/cgi/content/extract/343/23/1715>
Nakijima, Takeo, Yoshihiro Nishimura, Teruaki Nishiuma, Yoshikazu Kotani, Yasuhiro Funada, Hiroyuki Nakata, and Mitsuhiro Yokoyama. "Characteristics of Patients with Chronic Cough Who Developed Classic Asthma During the Course of Cough Variant Asthma: A Longitudinal Study." Respiration (2005) 72(6):606-611. 22 Jan. 2008 <http://content.karger.com/produktedb/produkte.asp?typ=fulltext&file=0000874 59>
Niimi, A., R. Amitani, K. Suzuki, E. Tanaka, E. Murayama, and F. Kuze. "Eosinophilic Inflammation in Cough Variant Asthma." The European Respiratory Journal (1998)11:1064-1069. 22 Jan. 2008 <http://www.erj.ersjournals.com/cgi/reprint/11/5/1064>