Proceedings of a Workshop on - The Havemeyer Foundation

Havemeyer Foundation Monograph Series No. 11
WORKSHOP SUMMARY
CONSENSUS STATEMENTS ON EQUINE
RECURRENT LARYNGEAL NEUROPATHY
General
1. The term recurrent laryngeal neuropathy
(RLN) is preferable to idiopathic laryngeal
hemiplegia (ILH) to describe a disease that
can manifest as laryngeal paresis or paralysis.
2. RLN is mainly a disease <strong>of</strong> the left side <strong>of</strong> the
larynx.
3. Clinically and endoscopically RLN occurs
with higher frequency in larger horses than
ponies, but the relationship between body size
and presence <strong>of</strong> disease is unresolved.
4. Abnormal inspiratory sounds during exercise,
commonly referred to as ‘roaring or whistling’
are a principal clinical sign <strong>of</strong> RLN.
5. RLN can cause reduced exercise performance.
6. Other dynamic inspiratory obstructions <strong>of</strong> the
upper airway such as axial deviation <strong>of</strong> the
aryepiglottic folds, arytenoid chondritis, and
nasopharyngeal collapse can cause similar
clinical signs to RLN.
Anatomy <strong>of</strong> the recurrent laryngeal nerve
1. The recurrent laryngeal nerve provides the
motor innervation <strong>of</strong> all the equine laryngeal
muscles except the cricothyroid, which is
innervated by the cranial laryngeal nerve.
2. The cell bodies <strong>of</strong> the lower motor neurons <strong>of</strong>
the recurrent laryngeal nerves are located in
the nucleus ambiguus.
3. The recurrent laryngeal nerve comprises
efferent and afferent nerves, principally
medium sized, myelinated axons that are not
discretely clustered according to their target
muscle.
4. The proportion <strong>of</strong> motor and sensory fibres in
the recurrent laryngeal nerves is unknown.
5. The right and left recurrent laryngeal nerves
loop around the subclavian artery and aortic
arch, respectively.
6. The left recurrent laryngeal nerve is the
longest nerve in the horse and is believed to
adhere tightly to the fascia <strong>of</strong> the aorta.
Pathology and pathogenesis
1. Although the disease clinically presents
almost exclusively as a consequence <strong>of</strong>
reduced abduction (see Table 1 for definition
<strong>of</strong> terminology) <strong>of</strong> the left arytenoid cartilage
due to dysfunction <strong>of</strong> the cricoarytenoideus
dorsalis muscle, the ipsilateral adductor
muscles are preferentially denervated in RLN.
2. The lesions <strong>of</strong> RLN, which include
preferential degeneration <strong>of</strong> large diameter
axons, more prominent distally, are indicative
<strong>of</strong> a distal axonopathy.
3. The presence <strong>of</strong> similar lesions in other long
nerves (eg phrenic or peroneal) <strong>of</strong> affected
horses needs more investigation to determine
if RLN is a mono – or a polyneuropathy.
4. RLN is not simply a result <strong>of</strong> nerve length;
although the recurrent laryngeal nerve <strong>of</strong> large
horses is about 3 m, other mammals have nerves
up to 6 m long (eg giraffe’s recurrent laryngeal
nerve) without neuronal degeneration.
5. The neuromuscular pathological changes
present in RLN indicate ongoing, continual or
intermittent injury <strong>of</strong> the recurrent laryngeal
nerve with repeated attempts at regeneration.
6. Horses with other recognised neuropathies,
for example stringhalt or Swedish knuckling
disease, can undergo complete recovery but it
is unclear if this can occur in RLN.
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