Prior Diagnosis and Treatment of Patients With Normal Results of Methacholine Challenge and Unexplained Respiratory Symptoms

¹ From the Asthma Centre of The Toronto Hospital, University of Toronto, Ontario, Canada

Objective: Previous research indicates that asthma has been underdiagnosed. However, we suspect that recent widespread attention to the underdiagnosis of asthma has led to an overdiagnosis of asthma in some settings. We therefore sought to examine prior diagnosis and treatment of patients referred to our facility and subsequently found to have no objective evidence of variable airflow limitation.

Design: Retrospective chart review.

Setting: Hospital-based asthma center.

Patients: A referred sample of 263 patients in whom a methacholine challenge (MCC) was conducted after evaluation by our pulmonologists; complete medical histories were available.

Main outcome measures: Prior respiratory diagnoses, duration of treatment with asthma medications, and diagnosis following assessment by our pulmonologists in 175 patients with a provocative concentration of the substance causing a 20% fall in FEV₁ (PC₂₀) greater than 8.0 mg/mL and 88 with a PC₂₀ of 8.0 mg/mL or less.

Results: Of those with a PC₂₀ greater than 8 mg/mL, a diagnosis of asthma or possible asthma prior to the challenge study was recorded by their primary care physician in 129 patients (74%). One hundred sixty of 172 patients (88%) with a PC₂₀ greater than 8 mg/mL were diagnosed as not having asthma by our pulmonologists; 109 of 172 patients (62%) had been previously treated with asthma medication(s). The mean duration of asthma treatment was 25.9±56.3 months, and there was no significant difference in the duration of treatment between this group and those who had a PC₂₀ of 8 mg/mL or less. Most of those treated received inhaled β₂-agonists and inhaled corticosteroids. Approximately 61% received two or more classes of medications.

Conclusions: The misdiagnosis of asthma occurs commonly in the referral practice of a tertiary care asthma center. The more frequent use of objective pulmonary function testing in primary practice might reduce the problem of delayed diagnosis and inappropriate therapy for respiratory symptoms.

Key Words: asthma • diagnosis • methacholine challenge

Submitted on August 23, 1995
Accepted on November 3, 2007

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