Sometimes a patient with asthma may present only with cough without other respiratory complaints.
Steps in the evaluation:
(1) methacholine challenge test
(2) response to asthma therapy
The methacholine challenge test has a negative predictive value of 100% for a patient with cough. The diagnosis of asthma can be excluded in a patient with a negative challenge test.
The patient with a positive methacholine challenge test is then treated for asthma (inhaled corticosteroids, inhaled beta-2 agonists, systemic corticosteroids). If the cough completely resolves after 6 to 8 weeks of therapy, then the diagnosis is confirmed. A patient with mixed cough (cough caused by more than one condition, such as GERD) may experience a partial cough relief.
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