Diagnostic workup of eosinophilic bronchitis

Imran Satia, MD, PhD, is an assistant professor in the Division of Respirology at McMaster University.

Can an increased level of eosinophils in the nasal cytology of a person with chronic cough indicate eosinophilic bronchitis as its cause?

Eosinophilic, or nonasthmatic eosinophilic bronchitis was first described by Freddy Hargreave and Peter Gibson in the late 1980s. It was based on a diagnosis of chronic cough, but with evidence of eosinophils in the sputum taken after doing sputum induction and getting patients to cough up their phlegm, examining the sputum, and identifying >2% to 3% of sputum eosinophils in the airways. When they did the bronchial challenge testing, like the methacholine challenge, they found no evidence of bronchial hyperresponsiveness, so they coined this term nonasthmatic eosinophilic bronchitis.

The ideal way to [establish] diagnosis is to actually assess the sputum cytology. Some people have tried to do nasal samples, but I don’t know of any evidence that suggests this is a good test for nasal biopsies.

Some people often use something called the exhaled nitric oxide [test] to help diagnose eosinophilic bronchitis because this is an easier test to do. But the sensitivity and specificity for this is highly variable, ranging from 75% to 90% (sensitivity), and there are no agreed cutoffs of what the fractional concentration of exhaled nitric oxide (FeNO) level should be. Should it be >40 ppb or should it be >50 ppb?

Some people also don’t have access to sputum cytology, so they may do bronchial biopsies to try and see if there are any eosinophils in the mucosa or submucosa to help make the diagnosis of nonasthmatic eosinophilic bronchitis. But in our clinical practice, measuring sputum eosinophilia is the easiest and most practical way to do it.