Background: Obesity and asthma both cause breathlessness, and there is a risk of misdiagnosis of asthma in patients who are obese. Impaired health-related quality of life (HRQoL) and increased BMI increase physician attendance rates, increasing this risk. We explored the possibility of misdiagnosis and the relationship between BMI, HRQoL, and other traditional measures of asthma severity in subjects who were obese with a doctor's diagnosis of asthma.
Methods: Data were obtained from subjects who were overweight with physician-diagnosed asthma screened as part of another study, including bronchial provocative concentration of methacholine to produce a 20% fall in FEV(1) (PC(20)) or reversibility to bronchodilators, HRQoL measured using generic (Short Form-36 [SF-36]) and disease-specific (St. George Respiratory Questionnaire and Impact of Weight on Quality of Life-Lite) questionnaires. The fraction of exhaled nitric oxide (Feno), height, weight, and atopic status were also recorded.
Results: Of 91 subjects (mean BMI, 38 kg/m(2); mean FEV(1)%, 85.8%; mean FEV(1)/FVC, 70.0%; mean Feno, 25.1 parts per billion taking a mean chlorofluorocarbon-beclomethasone-equivalent dose of 1,273.5 μg/d), 36.3% had no bronchial hyperresponsiveness (possible misclassification of asthma diagnosis.) The BMI and HRQoL were significantly related: The St. George Respiratory Questionnaire total (r = 0.33, P < .001), SF-36 physical health subtotal (r = -0.42, P < .001), SF-36 mental health subtotal (r = -0.39, P < .001), and Impact of Weight on Quality of Life-Lite total (r = 0.51, P < .001) showed no relationship to airways inflammation and bronchial reactivity. There was no significant difference in quality-of-life scores in subjects with or without bronchial hyperreactivity.
Conclusions: We found evidence of misdiagnosis of asthma in subjects who were obese. The BMI in subjects who were obese and had asthma negatively correlates with the HRQoL, which may relate to the diagnostic uncertainty and requires further exploration.
Trial registry: ISRCTN Register; No.: 54432221; URL: www.controlled-trials.com/isrctn.