Prevalence of over-/misdiagnosis of asthma in patients referred to an allergy clinic

Objective: Increasing asthma incidence may be due to an overall increase in asthma awareness by physicians, potentially resulting in overdiagnosis. One of the unique features of asthma is bronchial hyperresponsiveness, which can be assessed by methacholine bronchial challenge (MBC). Overdiagnosis may result in over- or mistreatment. The aims of this study were to describe the prevalence of the over-/misdiagnosis of asthma and the use of anti-asthmatic drugs in patients with asthma-like symptoms who had not yet undergone a respiratory function assessment to confirm the diagnosis of asthma. Methods: This was a retrospective study analyzing all MBCs performed by our Outpatient Allergy Clinic in a two-year period to confirm/exclude the diagnosis of asthma in patients referred by general practitioners and complaining of asthma-like symptoms. Anti-asthmatic medications used by the patients until the MBC date were recorded. Results: 43.8% of the reviewed MBCs were positive and 37.4% of the patients with a positive MBC were previously taking anti-asthmatic drugs (568.8 +/- 76.4mcg mean beclomethasone equivalents), compared to 51.2% of those patients with a negative MBC (464.8 +/- 57.8mcg). No differences were found in the daily doses of inhaled corticosteroids or other anti-asthmatic drugs, or in the duration of treatment before the assessment of bronchial hyperresponsiveness. Conclusions: A sizeable percentage of subjects who reported physician-diagnosed asthma had a negative MBC. Nevertheless, a greater proportion of negative MBC patients were taking anti-asthmatic drugs compared to those with a confirmed diagnosis of asthma, illustrating that the overdiagnosis of asthma may lead to over- and mistreatment of respiratory symptoms.