Methacholine Bronchoprovocation Test: A Useful Ancillary Test for Diagnosis of Hyperresponsiveness in Horses?

The clinical examination and the ancillary tests used in clinical routine may be poorly characteristics in horses suffering from subclinical inflammatory airway disease or in clinical remission of recurrent airway obstruction (RAO).

Methacholine bronchoprovocation test, which is used for diagnosis of human asthma, has been used in some studies in horses, but none have examined his potential diagnostic interest.

The objective of this study was to determine whether this test may represent an applicable and repeatable method for the diagnosis of an increased susceptibility to bronchospasm in horses, and whether there is a relationship between this test and the markers of inflammation in the bronchoalveolar lavage.

Eight horses (6 with RAO history and 2 controls) were used. They underwent bronchoprovocation tests 2 times at 24h interval. They were then tested before and after 7 days of an environmental challenge. Simultaneously, bronchoalveolar lavages were done for the measurement of several inflammatory markers.

The test has a good feasibility and significant repeatability. Dust exposure increased the bronchoreactivity, while it did not significantly affect other clinical and functional parameters or inflammatory makers.

In the future, the bronchoprovocation test could therefore find its place in clinical practice for the detection of asymptomatic horses which are susceptible to develop bronchospasm in poorer environmental conditions.