Proceedings of a Workshop on - The Havemeyer Foundation

Havemeyer Foundation Monograph Series No. 11
SALES: PROBLEMS IN THE DIAGNOSIS OF RLN –
AUSTRALASIAN PERSPECTIVE
B. H. Anderson
Ballarat Veterinary Practice, 1410 Sturt Street, Ballarat, Victoria 3350, Australia
In an ideal world treadmill video-endoscopy
would be used to determine the clinical
significance <strong>of</strong> varying degrees <strong>of</strong> recurrent
laryngeal neuropathy (RLN) identified during post
sale endoscopic examinations. This is not practical
and so the less perfect procedure <strong>of</strong> resting
endoscopy must be relied on. Unfortunately, this
technique will not predict with 100% accuracy
which horses will make a ‘whistling’ or ‘roaring’
noise at fast exercise.
In New Zealand and Australia a 5-point
grading system is used to help endoscopists
determine the clinical significance <strong>of</strong> RLN. Grade
1 and 2 laryngeal movements are considered
within normal limits. Grade 3 laryngeal
movements are equivocal. Grade 4 and 5 laryngeal
movements are due to clinically significant RLN
(supported by a number <strong>of</strong> treadmill studies
showing respiratory impairment during fast
exercise in these animals). Grade 4 and 5 horses
fail the post sale endoscopic examination.
Horses with Grade 3 laryngeal function pass
the post sale endoscopic examination. Endoscopy
in these horses reveals slight laryngeal asymmetry
at rest but full abduction can be achieved by the
arytenoid cartilage. However, activity is generally
reduced on one side (usually the left). Full
bilateral abduction can be stimulated either by
partial asphyxiation (nasal occlusion manoeuvre)
or by inducing swallowing, but is frequently not
sustained. Although some <strong>of</strong> these horses may
have impaired athletic performance, recent
treadmill studies (Lane 2000) indicate that in at
least 75% full bilateral arytenoid abduction is
maintained during fast exercise. Fortunately for
endoscopists at sales within the United Kingdom a
dynamic component is added to the testing
procedure by using ‘wind testing’ and this aid
helps improve accuracy in determining clinically
significant RLN. Under this system horses with
Grade 3 laryngeal movements that also make a
characteristic ‘whistle or roaring noise’ when
lunged at the canter, fail post sales examinations.
Without the benefit <strong>of</strong> an exercise test and because
the majority <strong>of</strong> Grade 3 horses have normal upper
respiratory tract function at fast exercise, failing
such horses in New Zealand and Australia would
be very problematic. This is an area <strong>of</strong> caveat
emptor and would seem to be fair to both vendors
and purchasers.
Using a static method to describe a dynamic
process has limitations. A wide range <strong>of</strong> defective
laryngeal movements exist and cut <strong>of</strong>f points can
never be as precise as one would wish. Problem
cases are likely. In addition, even apparently
normal horses (Grade 1 or 2 laryngeal movements
at rest) have been found to have abnormal
laryngeal movements (Grade 3–5 or dynamic
arytenoid collapse) (Kannegieter and Dore 1995;
Lane 2000) and respiratory noise when galloped
on the treadmill. Furthermore, it is sobering to
appreciate that the progression <strong>of</strong> RLN in
Thoroughbred horses to degrees which may be
clinically important is estimated as 5–15%,
(Anderson et al. 1997; Dixon et al. 2002). More
alarming for endoscopists however is that this
progression may occur quickly, over some few
weeks or months.
The challenge in the sales environment is to be
confident that a horse can fully abduct the
arytenoid cartilages. As a matter <strong>of</strong> quality
control, all horses with Grade 3 laryngeal
movements are examined by a second
veterinarian. In horses in which laryngeal abductor
function is questionable, video-endoscopic
examination is made and reviewed carefully to
determine that full symmetrical abduction <strong>of</strong> both
cartilages is present.
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