Prevalence of Arnold nerve reflex in subjects with and without chronic cough: Relevance to Cough Hypersensitivity Syndrome

Introduction: Cough is induced by stimulation of structures innervated by the vagus nerve, including the upper and lower airways and distal esophagus. The Arnold nerve reflex describes cough resulting from stimulation of the external auditory canal, which is innervated by the auricular branch of the vagus. We have recently reported the increased prevalence of this reflex in adults, but not children, with chronic cough, relative to healthy adult and pediatric subjects. The prevalence of the Arnold nerve reflex in patients with pulmonary disease but without chronic cough has not been investigated previously. Methods: Three hundred adults and 100 children with chronic cough, 50 adults with stable pulmonary disease but without chronic cough, as well as 100 adult and 100 pediatric volunteers, underwent evaluation consisting of stimulation of the external auditory canal of each ear with a cotton-tipped applicator. Cough occurring within 10 s of stimulation was considered induced by the intervention. Results: Arnold's nerve reflex was present in 23.3% of adults and 3% of children with chronic cough. The prevalence of the reflex was 2% among healthy adults and children. In adults with chronic cough, Arnold's nerve reflex was observed more commonly in women (29.3%) than men (10.5%), and was unilateral in the majority of patients (88.6%). In patients with respiratory disease but without chronic cough, Arnold nerve reflex was present in 2%. Conclusions: The greater than 11-fold prevalence of the Arnold nerve reflex in adults with chronic cough compared with healthy volunteers and adults with respiratory disease but without chronic cough, supports the concept of the Cough Hypersensitivity Syndrome (CHS), in which vagal hypersensitivity is proposed to underlie chronic refractory cough. The absence of increased prevalence among children with chronic cough suggests that CHS is an acquired condition, perhaps triggered by viral respiratory infection or other environmental factor.