Sensory hyperreactivity - a possible mechanism underlying cough and asthma-like symptoms

Background Investigations of patients referred for suspected asthma have re vealed a little-known group with symptoms suggesting hyperreactive airways in whom provocation with methacholine does not lead to bronchial obstructio n. The underlying mechanisms are not known, and no objective diagnostic met hod has been available. Methods Provocations by inhalation of capsaicin solutions in stepwise incre asing concentrations were used. Ten patients with asthma-like symptoms afte r exposure to nonspecific irritating stimuli, but without IgE-mediated alle rgy or demonstrable bronchial obstruction, were compared to 10 patients wit h verified bronchial asthma and 28 healthy controls. Results The patients with asthma-like symptoms reacted with cough in a dose -dependent way. The number of coughs was significantly greater than in asth matic patients and healthy controls. The latter two groups did not differ s ignificantly. Conclusions The capsaicin provocation test may be a valuable method for sho wing not only a greater cough sensitivity, but also asthma-like symptoms. T he pathophysiology underlying the symptoms may be related to increased sens itivity of free, overactive nerve endings in the respiratory mucosa. Theref ore, we suggest that this overreaction in the lower airways be called "sens ory hyperreactivity".