Mayo Clinic finds effective test to determine treatment for chronic cough

September 06, 2006

ROCHESTER, Minn. -- Mayo Clinic researchers have found that an asthma diagnostic test, the exhaled nitric oxide test, is an inexpensive, quick and easy way to determine whether inhaled corticosteroids will relieve a patient's chronic cough. Details will be presented in an abstract at the European Respiratory Society Meeting in Munich, Germany, Sept. 6.

"We're thinking this could be a significant development in the field of chronic cough," says Peter Hahn, M.D., Mayo Clinic pulmonologist and lead study investigator. "It could drastically change what we do for patients with chronic cough and also the guidelines for diagnosis and treatment of chronic cough. This very accurate -- but rather underused -- test could be used up front for all patients complaining of chronic cough, saving significant time and expense in other testing. It helps us get to the treatment and bring relief to the patient in the least invasive, fastest way possible."

An estimated 23 million Americans see their physicians each year for cough; it is the third most common reason a patient seeks a physician visit, according to the Mayo Clinic researchers. Chronic cough is variably defined as three to eight weeks of prolonged cough. Most patients see a physician because the cough disrupts their daily lives, says Dr. Hahn. The three major diagnoses that can cause chronic cough are: upper airway cough syndrome (also known as postnasal drip syndrome), asthma, and gastroesophageal reflux. Another diagnosis that affects fewer chronic coughers is non-asthmatic eosinophilic bronchitis.

The exhaled nitric oxide test measures inflammation in the lungs' bronchial tubes. The patient breathes into an analyzer four or five times over the course of 10 minutes. Abnormal scores indicate that the patient has asthma or possibly non-asthmatic eosinophilic bronchitis. Both can be effectively treated with inhaled corticosteroids. In these patients, inflammation irritates the airway and prompts coughing. Corticosteroids help reduce the inflammation, alleviating the cough.

This test is much easier for patients and predicts response to corticosteroid treatment better than a commonly used test, the methacholine challenge, according to Dr. Hahn.

This study was conducted via chart review of consecutive patients evaluated at Mayo Clinic for chronic cough using both exhaled nitric oxide and methacholine challenge testing between December 2004 and November 2005. During the study interval, 114 patients underwent methacholine challenge testing and measurement of exhaled nitric oxide as part of a chronic cough evaluation. Sixty-four of these were either started on inhaled corticosteroids or had their current dose increased to treat chronic cough. Forty-one patients had elevated exhaled nitric oxide levels. Of these, 36 (88 percent) had significant improvement in their chronic cough. Twenty-three patients with exhaled nitric oxide in the normal range also were started on inhaled corticosteroids, and only two had cough improvement. In contrast, 25 of 39 (64 percent) patients with a positive methacholine challenge test responded to inhaled corticosteroids, but up to 52 percent with a negative methacholine challenge test still had significant improvement of their chronic cough with inhaled corticosteroid therapy. Patients had documented follow-up ranging from four weeks to 12 months.

Study results suggest that measurement of exhaled nitric oxide accurately predicts patients' response to inhaled corticosteroids for chronic cough, according to the Mayo Clinic researchers.

"Patients with a positive, or abnormal, exhaled nitric oxide test had a strong likelihood of response to inhaled corticosteroids, whereas a negative, or normal, exhaled nitric oxide test virtually excluded response to the medication," says Dr. Hahn. "The accuracy of the exhaled nitric oxide test in predicting response to inhaled corticosteroids for chronic cough appears to be better than with methacholine challenge testing. This may potentially have a significant impact on how patients with chronic cough are evaluated and treated."

The next step needed in testing for chronic cough is a prospective study comparing the utility of the methacholine challenge versus the exhaled nitric oxide test, says Dr. Hahn.
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