1. Usefulness of FeNO in the diagnosis of chronic cough
Dr Poulose Vijo
Department of Respiratory & Critical Care Medicine
Changi General Hospital, SINGAPORE
Purpose
Non-acute cough (sub acute and chronic) can present as a huge diagnostic problem for clinicians, especially in the absence of a typical history or clinical features that would suggest an etiology. In these situations, FeNO (Fractional exhaled nitric oxide) can have an important role; as it can help identify cases of asthma or NAEB (non asthmatic eosinophilic bronchitis)1. Although sputum eosinophilia (>3%) is the commonly recommended test for NAEB, it is cumbersome to perform and is not practical in a patient who has a dry cough or cannot expectorate properly
Results
Methods
I performed a chart review of 200 prospectively identified cases of non-acute cough who were referred to my respiratory clinic over a 21/2 year period (March 2010 to October 2012) for diagnosis. FeNO testing was usually done when the diagnosis was not clear from the history, physical exam or chest radiograph in the initial visit. A FeNO level > 25 ppb was considered high. A diagnosis of NAEB was made in patients with a high FeNO, negative methacholine challenge test (MCT) and who responded to oral/inhaled steroids. Asthma was diagnosed in patients who had a high FeNO and positive MCT.
200 cough patients
24 had FeNO done
About 10 % (24 patients) of the referred cases had FeNO testing. Three patients refused or defaulted further work-up. Among the remaining 21 cases, twelve had MCT performed on them (see the flow chart for etiological outcomes). The 4 NAEB patients had FeNO levels of 29, 34, 57 and 59 ppb respectively. The 2 asthma patients had levels of 29 and 135
8 had high FeNO
16 had normal FeNO
2 no diagnosis
Final diagnosis
7 post nasal drip syndrome (PNDS)
2 GERD
2 PNDS + GERD
2 occupational bronchitis
3 no diagnosis
3 NAEB
1 NAEB + PNDS
2 asthma
Conclusion & Clinical implications
In patients where the initial evaluation does not suggest an etiology, FeNO testing can be useful, especially when done in conjunction with MCT
1. Exhaled nitric oxide measurement is useful for the exclusion of nonasthmatic eosinophilic bronchitis in patients with chronic cough.
Oh MJ, Lee JY et al, Chest 2008 Nov;134(5):990-5