BACKGROUND: Little is known about the factors that determine outcome in asthma. The purpose of this study was to describe the relation of various factors of potential importance to the rate of decline in lung function in adults with intrinsic and extrinsic asthma. METHODS: Of 180 asthmatic patients, 143 (79%) participated in a 10 year follow up examination. At the time of enrollment all patients underwent certain tests for asthma (case history, total IgE, skinprick tests, the radioallergosorbent test (RAST), histamine release from basophil leucocytes, and specific bronchial provocations). On the basis of these tests 94 patients had intrinsic asthma and 49 extrinsic asthma. RESULTS: Patients with intrinsic asthma had an annual decline in FEV1 of 50 ml, whereas those with extrinsic asthma had a decline of 22.5 ml; the rate of decline of lung function increased with increasing age in both groups. An inverse relation between initial FEV1 and decline in FEV1 (the "horse racing effect") was found for the patients with extrinsic asthma but not for the patients with intrinsic asthma. There was no relation between rate of decline in lung function and number of cigarettes smoked. A high degree of airway variability--that is, reversibility in FEV1--at the time of enrollment was found to be associated with a steeper decline in lung function in patients with intrinsic asthma, whereas increasing degrees of obstruction (decreasing FEV1/VC ratio at enrollment) and need for treatment with corticosteroids were associated with a more pronounced decline in FEV1 in patients with extrinsic asthma. CONCLUSIONS: The rate of decline in lung function is greater in patients with intrinsic asthma than in patients with extrinsic asthma; the prognosis for intrinsic and extrinsic asthma is to some extent influenced by different factors, which suggests that the pathogenetic mechanisms underlying intrinsic and extrinsic asthma may differ.
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