A SYSTEMATIC EVALUATION OF MECHANISMS IN CHRONIC COUGH

We tested the hypothesis that hyperresponsiveness of the upper airway (UAHR) is present in patients with chronic cough of diverse etiology. We determined the frequency of bronchial hyperresponsiveness (BHR), hy perresponsiveness of the upper airway, sputum eosinophilia, pulmonary aspiration, and psychological symptoms in adults with chronic cough. C onsecutive adults (n = 30) presenting to a tertiary referral clinic wi th chronic cough were compared with a group of 20 asymptomatic adults. Measurements included histamine provocation testing with measurement of flow volume curves to determine inspiratory and expiratory airflow obstruction; hypertonic saline induced sputum for analysis of eosinoph ils, mast cells and lipid-laden macrophages; and a validated psycholog ical symptom questionnaire. Symptomatic rhinitis and gastroesophageal reflux were common causes of chronic cough. BHR occurred in seven pati ents (23%) and in no control subjects (p < 0.05). UAHR occurred in 40% of patients with cough and in four (20%) control subjects (p > 0.05). Eosinophils were present in the sputum of more patients with cough th an control subjects (50% versus 19%; p < 0.05). High degrees of eosino philia were present in six patients with cough, including three withou t BHR. No subject had significant lipid-laden macrophages. There was g reater somatization in patients with chronic cough; ten subjects score d in the clinically significant range (p < 0.05). Abnormalities in one or more of these tests were 7.67-fold (95% CI 1.83-34.52) more likely to occur in cough patients than control subjects. We conclude that ch ronic cough is a nonspecific symptom that is associated with several a pparently unrelated mechanisms. These include UAHR, somatization, BHR, and eosinophilic bronchitis. UAHR cannot be implicated as a single un ifying mechanism. These findings emphasize the need to systematically evaluate several different causes of cough in patients who present wit h chronic cough.