Two variants of occupational asthma separable by exhaled breath nitric oxide level

SummaryExhaled nitric oxide (FENO) has been used as a marker of asthmatic inflammation in non-occupational asthma, but some asthmatics have a normal FENO. In this study we investigated whether, normal FENO variants have less reactivity in methacholine challenge and smaller peak expiratory flow (PEF) responses than high FENO variants in a group of occupational asthmatics.MethodsWe measured FENO and PD20 in methacholine challenge in 60 workers currently exposed to occupational agents, who were referred consecutively to a specialist occupational lung disease clinic and whose serial PEF records confirmed occupational asthma. Bronchial responsiveness (PD20 in methacholine challenge) and the degree of PEF change to occupational exposures, (measured by calculating diurnal variation and the area between curves score of the serial PEF record in Oasys), were compared between those with normal and raised FENO. Potential confounding factors such as smoking, atopy and inhaled corticosteroid use were adjusted for.ResultsThere was a significant correlation between FENO and bronchial hyper-responsiveness in methacholine challenge (p = 0.011), after controlling for confounders. Reactivity to methacholine was significantly lower in the normal FENO group compared to the raised FENO group (p = 0.035). The two FENO variants did not differ significantly according to the causal agent, the magnitude of the response in PEF to the asthmagen at work, or diurnal variation.ConclusionsOccupational asthma patients present as two different variants based on FENO. The group with normal FENO have less reactivity in methacholine challenge, while the PEF changes in relation to work are similar.