Proceedings of a Workshop on - The Havemeyer Foundation

Equine Recurrent Laryngeal Neuropathy
EDITORS’ FOREWORD
Equine laryngeal paralysis, most commonly
attributed to the syndrome <strong>of</strong> recurrent
laryngeal neuropathy (RLN), is long
recognised as the most important equine upper
airway disease <strong>of</strong> horses. It can cause exercise
intolerance and stridor during fast work and in
the rare bilateral cases, and severe respiratory
distress, even in the resting horse. Despite is,
there are still large gaps in our knowledge <strong>of</strong> its
aetiology, pathogenesis, methods <strong>of</strong> assessment
and the critical evaluation <strong>of</strong> its treatment.
Between 20 and 30 years ago, there was
significant research into the disease, but there
have been few substantive studies since then.
To promote further basic and applied
research into this disease it seemed worthwhile
to review current knowledge about this disease.
This was the main purpose <strong>of</strong> the present
workshop and we invited eminent neurologists to
review knowledge <strong>of</strong> the aetiology <strong>of</strong> RLN and to
compare it with other equine peripheral
neuropathies. It was also valuable to gain an
overview <strong>of</strong> some comparative aspects <strong>of</strong> RLN
with laryngeal paralysis in other species. By
obtaining consensus on our present knowledge,
we went on to suggest areas for productive future
research. For example, are sub-clinical
neuropathies <strong>of</strong> other long peripheral nerves
present in horses with RLN?
As well as established research scientists, our
delegates included practitioners who undertake
upper airway examination <strong>of</strong> young horses at
sales. Outlining the difficulties and practical
problems encountered by clinicians in Europe,
America and Australia, they provided insight
into the incidence and possible progression <strong>of</strong>
this disease. Currently, endoscopy is the gold
standard for assessing laryngeal dysfunction in
the horse. For clinicians to communicate
effectively with each other on RLN cases, a
variety <strong>of</strong> grading systems are in use. One aim <strong>of</strong>
the workshop was to reach a consensus as to
which endoscopic grading system should be
advocated universally. After lengthy discussion,
we reached a consensus and time will tell if the
international community accepts the suggested
system. Some studies have shown that, even with
well-defined endoscopic criteria and grading
systems, inter-observer variation can occur in the
endoscopic grading <strong>of</strong> laryngeal function. The
upcoming results <strong>of</strong> an interactive video
presentation conducted at the workshop may
support or refute this. Even allowing for
individual variation in interpretation, it is well
established that the endoscopic findings in some
horses (and foals) may differ from time to time.
Presentations addressed the progressive nature <strong>of</strong>
the disease, especially in some older horses.
The advent <strong>of</strong> endoscopic examination
during exercise on a high-speed treadmill has
revealed that assessment <strong>of</strong> laryngeal
dysfunction in the resting horse does not always
reflect what occurs during high speed exercise.
In addition, upper airway obstructions in horses
are not always due to laryngeal paralysis. The
results <strong>of</strong> large surveys <strong>of</strong> both <strong>of</strong> these topics
were presented. Recently, it was found that
horses can suffer bilateral laryngeal paralysis in
the presence <strong>of</strong> liver disease and following
general anaesthesia and comparison <strong>of</strong> these
cases with RLN may cast further light on the
aetiopathogenesis <strong>of</strong> both disorders.
In the last 2 decades there have been many
clinical and physiological studies <strong>of</strong> the efficacy
<strong>of</strong> treatments for equine laryngeal paralysis.
These have addressed both the improvement <strong>of</strong>
airway function and elimination <strong>of</strong> abnormal
sounds. The various treatments currently in use
were reviewed including the promising
neuromuscular pedicle graft. Comparisons were
made with the treatment <strong>of</strong> laryngeal paralysis in
the dog.
It was agreed that future areas for research
should include investigations into the aetiovi