Capsaicin cough sensitivity in allergic asthmatic patients increases during the birch pollen season

A change in neural responsiveness may occur as the result of allergic inflammation in the lower airways as well as in the upper airways. In the lower airways, capsaicin cough sensitivity is known to reflect sensory neural reactivity. The aim of this study was to establish whether allergic inflammation changes airway neural sensory reactivity during prolonged allergen exposure. Ten nonsmoking patients with birch pollen-allergic asthma performed a capsaicin inhalation challenge twice, once in the off-pollen season and once during the pollen season. The number of coughs and symptoms induced by capsaicin were recorded and compared with those of healthy control subjects. The response to capsaicin, expressed as number of coughs, increased in a dose-dependent manner during both tests. Before the season, the response was similar to that of healthy control subjects, but during the pollen season, the reactivity was significantly increased. Variations in forced expiratory volume in 1 second were not significant before and after each challenge, and values did not change during the pollen season as compared with the winter season. Sensory reactivity in allergic asthmatic patients may be increased during prolonged allergen exposure as during the pollen season. This finding suggests that allergic inflammation in the lower and/or upper airways may trigger neurogenic mechanisms of significant clinical importance.