Substance P-immunoreactive nerves in endobronchial biopsies in cough-variant asthma and classic asthma

Background: Unlike classic asthma, cough-variant asthma does not show any evidence of airway obstruction. The main symptom is a dry cough with little known pathophysiology. Hypersensitivity of the cough receptors in cough-variant asthma and an increase in the sensory nerve density of the airway epithelium in persistent dry cough patients have been reported. Therefore, it is possible that there is a higher sensory nerve density in cough-variant asthma patients than in classic asthma patients. Objectives: This study was undertaken to compare the substance P (SP)-immunoreactive nerve density in mucosal biopsies of cough-variant asthma patients, classic asthma patients, and in control subjects. Methods: Bronchoscopic biopsies were performed in 6 cough-variant asthma patients, 14 classic asthma patients, and 5 normal controls. The tissues obtained were stained immunohistochemically. The SP-immunoreactive nerve density was measured in the bronchial epithelium using a light microscope at 400x magnification. Results: SP-immunoreactive nerve density for the cough-variant asthma group was significantly higher than that of the classic asthma group (p = 0.001), and of the normal control group (p = 0.006). Conclusions: It is possible that a sensory nerve abnormality within the airway may be related to hypersensitivity of the cough receptor, and that this may be one of the pathophysiologies of cough-variant asthma.