A preliminary study of PEFR monitoring in patients with chronic cough.

It is important to make a differential diagnosis of cough variant asthma in patients with chronic cough. To examine whether or not peak expiratory flow rate (PEFR) is useful for the differential diagnosis of cough variant asthma in such patients, diurnal variation rates of PEFR were calculated in 23 patients who presented with dry cough lasting four or more weeks and who showed no abnormalities on chest radiographs. None of the patients had wheezes, and pulmonary function testing at the time of visit to the hospital revealed no abnormalities. During the control period, the mean diurnal variation rate of PEFR in 23 patients was 16.3 +/- 7.9%. Six, nine and eight patients had PEFR diurnal variations rates of <10% (Group 1), 10-19% (Group 2), and > or = 20% (Group 3), respectively. At week 3 of treatment with bronchodilators, only Group 3 showed a significant decrease in PEFR diurnal variation rate from 25.7% to 10.1%. The cough score decreased significantly in Group 3 only. These patients had enhanced bronchial hyperresponsiveness and showed eosinophils in induced sputum, leading to the diagnosis of cough variant asthma (CVA). After making the diagnosis of CVA, an inhaled corticosteroid or a Th2 cytokine production inhibitor suplatast tosilate was administered to patients; consequently, they showed no recurrence of cough. PEFR monitoring allowed the detection of morning dip and was suggested to be potentially useful for the differential diagnosis of cough variant asthma in patients with chronic cough.