Proceedings of a Workshop on - The Havemeyer Foundation

Equine Recurrent Laryngeal Neuropathy
5-POINT GRADING SYSTEM OF LARYNGEAL
FUNCTION IN HORSES DURING QUIET BREATHING
J. G. Lane
Department <strong>of</strong> Clinical Veterinary Science, University <strong>of</strong> Bristol, Langford House, Langford, Bristol,
BS40 5DU, UK
Clinicians are generally obsessed with scoring or
grading disorders which they encounter, whether it
be the severity <strong>of</strong> feather pecking in chickens, hip
dysplasia in dogs or function <strong>of</strong> the equine larynx.
The purpose is invariably to provide an objective
and repeatable method to document observations.
This 5-point scheme to grade the endoscopic
perception <strong>of</strong> equine laryngeal motility at rest in
the stable, including on return from exercise – quiet
breathing has been used at Bristol since the early
1980s and in Australasia since 1993 (Lane 1993;
Kannegeiter and Dore 1995). It is not very different
from the 4-point scale used in North America
(Rakestraw et al. 1991) and has been continued
simply because it has been found to be workable in
everyday equine laryngological practice.
Grade 1: All movements, both adductory and
abductory are synchronised and symmetrical
regardless <strong>of</strong> whether sedated or examined before
or after exercise. A ‘mirror’ effect is achieved
through a perspective artifact whereby the right
arytenoid appears less abducted when the
endoscopy is performed through the right nostril,
and the left is similarly less abducted when the
larynx is viewed via the left nasal chamber.
Grade 2: All major movements are symmetrical
and a full range is achieved. Transient asynchrony,
flutter or delayed opening may be seen (Baker
1983).
Grade 3: Asymmetry <strong>of</strong> the rima glottidis at rest
due to reduced motility by the left arytenoid
cartilage and vocal fold. On occasions, typically
after swallowing or during the nostril closure
manoeuvre, full symmetrical abduction is achieved.
Grade 4: There is consistent asymmetry <strong>of</strong> the
rima glottidis but with some residual active
motility by the left arytenoid cartilage and vocal
fold. Full abduction is not achieved at any stage.
Grade 5: True hemiplegia. There is obvious and
consistent asymmetry <strong>of</strong> the rima glottidis with no
residual active motility by the left arytenoid
cartilage and vocal fold. No responses to the ‘slap’
test are provoked.
At the request <strong>of</strong> a major owner/breeder videoendoscopic
recordings were made <strong>of</strong> the upper
respiratory tracts <strong>of</strong> 3,497 yearlings during a 15 year
study and the findings have been reviewed. The
study has provided a unique opportunity to estimate
the prevalence <strong>of</strong> laryngeal disorders as and to assess
the distribution <strong>of</strong> functional anomalies in the
Thoroughbred. Although the subjects represent an
elite group <strong>of</strong> horses on the basis <strong>of</strong> genetic
selection, unlike previous investigations (Pascoe et
al. 1981; Raphael 1982; Baker 1983; Lane et al.
1987; Sweeney et al. 1991), these were unbroken
and, therefore untried animals. Initially,
approximately half <strong>of</strong> the yearlings had been
purchased, some privately and some at auction, and
half were homebred. In recent years the majority <strong>of</strong>
the yearlings examined have been homebred and yet
the distribution <strong>of</strong> the findings has remained
constant. The findings in regard to the distribution <strong>of</strong>
functional grading are shown in Table 1.
The 12 yearlings for which no grade was
assigned included 7 afflicted with the fourth
branchial arch defect syndrome and an additional
5 with malfunction on the right side and where no
physical explanation was discovered.
TABLE 1: Laryngeal function grading <strong>of</strong> 3,497
yearlings
RLN 1 2 3 4 5 Not
grading
graded
784 2006 617 69 9 12
% 22.4 57.4 17.6 2.0 0.026 0.34
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