Evaluation of methacholine challenge test results in patients with chronic unexplained cough

Introduction: Asthma is one of the most common chronic diseases in adults characterized by variable airway obstruction. Asthma is diagnosed with wheezing and shortness of breath, however it sometimes manifests as a chronic cough that is difficult to diagnose and requires spirometry stimulation tests. Objectives: This study aimed to investigate the relationship between methacholine test results and respiratory symptoms in patients with chronic unexplained cough. Patients and Methods: In this cross-sectional study, 102 patients with chronic cough and normal basal spirometry were included. All patients underwent a methacholine challenge test, and their airway irritabilities were assessed. Then, the relationship between methacholine test results and clinical symptoms and also demographic characteristics were investigated. Results: Of 102 patients, 69 (67.6 %) and 33 (32.4%) were female and male, respectively. Most of patients were non-smoker (90.2%). Around 25 (24.5%) patients had a positive methacholine test. Rhinitis had a statistically significant difference between patients with positive and negative tests (positive test group: 48%, negative test group: 23.4%; P = 0.01). Postnasal discharge was reported in 60% of positive methacholine test patients, which was significant compared to the negative group (36.4%; P = 0.03). Most patients who had positive tests were housewives (76%). Logistic regression showed that female gender (OR: 7.75, 95% CI: 1.7-35.2), postnasal discharge (OR: 3.19, 95% CI: 1.25-8.2), rhinitis (OR: 3.02, 95% CI: 1.17-7.79), and allergy symptoms OR: 3.51, 95% CI: 1.35-9.18) were directly associated with a positive methacholine test. Conclusion: The presence of airway hypersensitivity, postnasal discharge, allergic rhinitis, female gender and the housewife’s job were strongly associated with a positive methacholine test.