Proceedings of a Workshop on - The Havemeyer Foundation

Havemeyer Foundation Monograph Series No. 11
Guidelines for endoscopic examination for the
purpose <strong>of</strong> laryngeal evaluation
1. Evaluation should be performed with as little
restraint as needed for safety <strong>of</strong> horse and
personnel.
2. The use <strong>of</strong> chemical restraint can alter
laryngeal function.
3. To achieve consistency in the endoscopic
appearance <strong>of</strong> the larynx, it is recommended
that the same nostril be used routinely for
introduction <strong>of</strong> the endoscope.
4. The initial endoscopic examination should be
conducted before rather than after exercise.
This allows observation <strong>of</strong> a wider range <strong>of</strong>
laryngeal movements.
5. During the endoscopic examination, laryngeal
function should be observed during quiet
breathing, swallowing and nasal occlusion.
Clinical grading <strong>of</strong> RLN
1. Although a number <strong>of</strong> grading systems are
available and validated, they consistently
agree on the following:
a) Inability to achieve full abduction <strong>of</strong> the
affected arytenoid cartilage during
examination is likely to be associated with
compromised respiratory function during
exercise.
b) Glottic asymmetry at end-exhalation and
asynchronous arytenoid movement during
inhalation are not cause for concern as long as
such horses can attain and maintain full
bilateral abduction <strong>of</strong> their arytenoid
cartilages.
2. The grading systems shown in Tables 2 and 3
is recommend by participants in the workshop.
3. There was no consensus on the functional
significance <strong>of</strong> obtaining full arytenoid
abduction that is not maintained symmetrically.
4. In the majority <strong>of</strong> horses, laryngeal function
remains constant over time, but in some
horses, laryngeal function can deteriorate over
a few weeks to years regardless <strong>of</strong> initial
endoscopic appearance.
5. Endoscopic evaluation <strong>of</strong> the larynx in
weanlings for presence <strong>of</strong> RLN is an
unreliable predictor <strong>of</strong> their laryngeal
endoscopic appearance as yearlings.
Other diagnostic procedures
1. Other tests <strong>of</strong> recurrent laryngeal function
include palpatory and endoscopic assessment
<strong>of</strong> the thoraco-laryngeal reflex (‘slap test’) and
measurement <strong>of</strong> nerve conduction velocity, ie
electrolaryngeogram. Currently, none <strong>of</strong> these
procedures is believed to be as effective as
endoscopic examination for diagnosing RLN.
TREATMENT OF CLINICAL SIGNS
ASSOCIATED WITH RLN
1. Surgical treatments used for relief <strong>of</strong> the
clinical signs <strong>of</strong> RLN include ventriculectomy
with or without vocalcordectomy, prosthetic
laryngoplasty, various degrees <strong>of</strong>
arytenoidectomy, and nerve muscle pedicle
grafts (reinnervation surgery).
2. These procedures vary in their efficacy in the
reduction <strong>of</strong> abnormal exercise related sounds
and the relief <strong>of</strong> airway obstruction.
3. Most <strong>of</strong> the following conclusions are based
on studies in experimentally induced laryngeal
hemiplegia. In the following section ‘RLN’
signifies the naturally occurring condition.
Abnormal upper respiratory sounds
1. Prosthetic laryngoplasty alone significantly
reduces the abnormal upper airway noise in
RLN afflicted horses.
2. Following prosthetic laryngoplasty, there is no
clear correlation between the degree <strong>of</strong>
residual upper respiratory noise and the
magnitude <strong>of</strong> surgical arytenoid abduction.
3. The degree <strong>of</strong> noise reduction after
laryngoplasty may be more a factor <strong>of</strong> stability
<strong>of</strong> the arytenoid cartilage rather than the
degree <strong>of</strong> arytenoid abduction.
4. Bilateral ventriculo-cordectomy can reduce
abnormal upper airway sounds in horses with
experimentally induced left laryngeal
hemiplegia.
5. Unilateral ventriculo-cordectomy can reduce
abnormal upper airway sounds in RLN
afflicted horses.
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