| Summary: | Chronic cough is a common problem in patients visiting physicians and its prevalence in different populations range from 3 to 40%. Postnasal drip, asthma and gastroesophageal reflux are the known cause of chronic cough. Although diagnosis of asthma is usually made by clinical signs and spirometeric results, methacholine challenge test is a good diagnostic test in patients who show normal physical examination and spirometeric results. In this study, the results of methacholine challenge test in chronic cough patients are investigated. This is a cross sectional study performed on patients suffering from chronic cough (over 8 weeks), who went to Pulmonary Disease Clinic of Imam Khomeini Hospital in 2006. Postnasal drip, gastroesophageal reflux was evaluated and ruled out in all patients. Then they were tested by methacholine inhalation using low to high doses of methacholine. The results of test was defined as 20% fall in FEV1 and its relationship with age, sex, history of allergic disease, family history of asthma and smoking status was investigated. 81 patients (36 female and 45 male) entered this study who had mean age of 32.5 ± 13.06 years. 81.5% of patients had never smoked or closed contact with smokers, 6.2% were passive smokers, 8.6% were smokers and 3.7% had quit smoking. 37% had suffered from chronic cough less than 6 months, 11% for 6-11 months and 52% for more than 12 months. In 26% of patients, family history of asthma was present and 34.5% had a history of one type of allergy. In 29.5% the results of methacholine challenge test was positive, among them 45.8% showed an intense response and 54.2% a moderate response. The test results and its intensity had no statistically significant relationship with age, sex, smoking status, the duration of cough and family history of asthma, but the relationship between methacholine challenge test and the history of allergic disease was significant. Methacholine challenge test can be used as a diagnostic test in patients suffering from chronic cough of unknown origin and patients whose clinical and paraclinical finding are normal. A positive test indicates hypersensitivity of airways which can be used for planning their treatment.
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