A new study claims that more than a third of obese asthmatic patients had no evidence of bronchial hyperresponsiveness, suggesting frequent misdiagnosis of breathlessness.

Researchers at the Countess of Chester Hospital (COCH; United Kingdom) and Liverpool University (United Kingdom) conducted an observational study of 91 obese patients with physician-diagnosed asthma to examine associations among obesity, health-related quality of life, and asthma diagnosis. All of the participants had a body mass index (BMI) higher than 30, did not smoke, and were taking asthma medication. The participants completed generic, respiratory, and obesity-related quality-of-life questionnaires. They also underwent atopy testing, methacholine challenge for bronchial hyperresponsiveness, and assessment of airway inflammation as reflected by the fraction of exhaled nitric oxide (FeNO).

The results showed no consistent correlations between FeNO and the questionnaires, and BMI correlated negatively with several domains within the questionnaires. Measures of lung function had no significant associations with health-related quality of life. A comparison of patients with and without bronchial hyperresponsiveness showed that the hyperresponsive patients were younger; had lower values on measures of lung function and higher values for FeNO; were more likely to be atopic; and were more likely to be ex-smokers. The study was published in the August 2011 issue of Chest.

“Since health-related quality of life and asthma control are related, it is easy to see how health impairments arising from obesity could be attributed to asthma, further increasing the likelihood of a misdiagnosis,” said lead author Stephen Scott, MD, of the COCH department of respiratory medicine. “The variable that correlated strongest with degree of health impairment was BMI rather than other traditional markers of asthma severity or airway inflammation.”

The prevalence of physician-diagnosed asthma continues to increase, in part, due to an association between obesity and asthma. Obese patients often exhibit asthma-like symptoms, arising from the effects of increased BMI on lung volumes, increased effort to breathe, and increased release of adipokines. Breathlessness is a common finding in both asthma and obesity, creating a further potential for misdiagnosis.

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