Chronic Cough Due to Asthma: Evaluation
If reversible airflow obstruction is demonstrated in a patient with chronic cough, empiric therapy for asthma is appropriate, However, a patient with chronic cough due to asthma may present a diagnostic challenge, because physical examination and pulmonary function test results can be entirely normal, In this setting, bronchoprovocation testing with inhaled methacholine should be used to document the presence of bronchial hyperresponsiveness and, therefore, the diagnosis of asthma, It must be stressed, however, that the presence of bronchial hyperresponsiveness in a patient with chronic cough is merely consistent with, but is not diagnostic of, CVA, A definitive diagnosis of CVA can only be made after the documented resolution of cough with specific treatment of asthma, Conversely, given its very high negative predictive power, a negative methacholine inhalation challenge (MIC) test result essentially excludes asthma from the differential diagnosis of chronic cough.
In a patient suspected of having CVA but in whom physical examination and spirometry findings are nondiagnostic, MIC testing should be performed to confirm the presence of asthma. However, a diagnosis of CVA is established only after the resolution of cough with specific antiasthmatic therapy. If MIC testing cannot be performed, empiric therapy should be given; however, a response to steroid therapy will not exclude nonasthmatic eosinophilic bronchitis as an etiology of the patient’s cough.
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Other conditions may suggest the diagnosis of asthmatic cough, Postviral or postinfectious cough (discussed in detail elsewhere in this supplement) typically presents as a persistent, dry cough in a previously healthy person in whom all other symptoms of the inciting upper respiratory tract infection resolved weeks or months earlier, Although this condition is not asthma, the patient with postviral cough may have dyspnea and wheezing, reversible airflow obstruction as demonstrated by spirometry, and a positive MIC test result due to transient, viral upper respiratory tract infection-induced bronchial hyperresponsiveness.
In general, the therapeutic approach to CVA is similar to that of the typical form of asthma, Partial improvement is often achieved after 1 week of inhaled bronchodilator therapy, but the complete resolution of cough may require up to 8 weeks of treatment with inhaled corticosteroids.