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Asthma Test for Chronic Cough

Test Could Help Doctors Better Treat Chronic Cough
By
WebMD Health News
Reviewed by Louise Chang, MD

Sept. 6, 2006 -- An asthma test may change the way doctors evaluate and treat chronic cough.

Researchers at the Mayo Clinic today reported that a test called the exhaled nitric oxide test, commonly used for asthma patients, can help predict which chronic cough patients would be helped by inhaled corticosteroids.

In the exhaled nitric oxide test, the patient breathes into a device four or five times over 10 minutes. The device then measures nitric oxide in the patient's exhaled air.

The test isn't new. Currently, it is used to look for inflammation of the airways, a symptom of asthma.

But the test may also help evaluate and guide treatment of chronic cough, which is a cough that lasts more than eight weeks, note Peter Hahn, MD, and colleagues at the Mayo Clinic in Rochester, Minn.

Hahn's team presented promising results for the exhaled nitric oxide test today at the 16th European Respiratory Society Congress, held in Munich, Germany.

'Drastic Change' Ahead?

"We're thinking this could be a significant development in the field of chronic cough," Hahn says, in a Mayo Clinic news release.

"It could drastically change what we do for patients with chronic cough and also the guidelines for diagnosis and treatment of chronic cough," he adds.

Chronic cough is usually due to asthma, postnasal drip, or gastroesophageal reflux (GERD), the researchers note. A less common cause is eosinophilic bronchitis.

Asthma and eosinophilic bronchitis can be treated with inhaled corticosteroids, which combat inflammation in the airways to reduce asthma symptoms.

In their study, Hahn's team reviewed the medical charts of 114 chronic cough patients seen at the Mayo Clinic.

The patients had taken the exhaled nitric oxide test. They had also performed methacholine challenge testing, in which patients inhale a chemical called methacholine as part of a lung function test.

Of those two tests, the exhaled nitric oxide test was better at predicting which chronic cough patients would be helped by inhaled corticosteroids, the study shows.

A total of 47 patients had high levels of exhaled nitric oxide. Of those patients, 41 started using inhaled corticosteroids, and 36 noted improvement in their cough.

Another 65 patients had normal levels of exhaled nitric oxide. Twenty-three began using inhaled corticosteroids. But only two of those patients reported cough improvement, the researchers write.

In short, inhaled corticosteroids were only likely to help ease chronic cough in patients with high levels of exhaled nitric oxide.

Methacholine challenge testing wasn't as specific at predicting which patients would be helped by steroid treatment, the study shows.

The exhaled nitric oxide test is "very accurate but rather underused," Hahn says.

He adds that the 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," Hahn says.

Hahn calls for further studies of the exhaled nitric oxide test in patients with chronic cough.

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