Proceedings of a Workshop on - The Havemeyer Foundation

Equine Recurrent Laryngeal Neuropathy
LARYNGEAL PARALYSIS IN DOGS
P. M. Dixon and K. M. Pratschke
Division <strong>of</strong> Veterinary Clinical Studies, The University <strong>of</strong> Edinburgh, Easter Bush Veterinary Centre,
Easter Bush, Midlothian EH25 9RG, UK
NON-IDIOPATHIC LARYNGEAL PARALYSIS
Hereditary forms <strong>of</strong> laryngeal paralysis, that are
part <strong>of</strong> a general neuropathy, are described in the
Bouvier des Flandres, Dalmation, Rottweiler,
Siberian husky (and crosses) and white coated
German shepherd (van Haagen et al. 1978; Braund
et al. 1994; Mahony et al. 1998; Ridyard et al.
2000). Inheritance patterns have been established
in Bouvier des Flandres (van Haagen et al. 1981)
and Dalmation (Braund et al. 1994). Dogs affected
with congenital laryngeal paralysis are typically
less than 7 months old at presentation and as they
are part <strong>of</strong> a more generalised polyneuropathy or
myopathy, they carry a poor prognosis. Congenital
laryngeal paralysis has been less commonly
described in other breeds, including toy breeds.
In older dogs, acquired laryngeal paralysis may
also manifest as part <strong>of</strong> a peripheral diffuse
neuropathy (Braund et al. 1989), in association with
myasthenia gravis, hypothyroidism (Gaber et al.
1985), hypoadrenocorticism and lead or
organophosphate poisoning. Laryngeal paralysis
can also follow direct trauma to the recurrent
laryngeal nerves, eg bite wounds, aggressive use <strong>of</strong>
choke chains; or during thyroid, oesophageal,
tracheal (prosthetic ring implants) or cervical spine
surgery. It can also occur following damage to the
recurrent laryngeal nerves by aggressive neck
tumours (eg thyroid neoplasms) or mediastinum (eg
lymphosarcoma). Ankylosis <strong>of</strong> the cricoarytenoid
joint has also been described as a cause <strong>of</strong> laryngeal
dysfunction in the dog, (but not the horse).
IDIOPATHIC LARYNGEAL PARALYSIS
Despite the extensive lists <strong>of</strong> aetiologies <strong>of</strong> canine
laryngeal paralysis, most are due to unknown
causes, as is the case with horses and are termed
canine idiopathic laryngeal paralysis. This
typically affects large breeds, such as Labradors,
retrievers, Afghans, and Irish setters and has been
recorded less commonly in smaller breeds and cats.
One study showed that subclinical, unilateral or
bilateral laryngeal paresis or paralysis was present
in 25% <strong>of</strong> dogs undergoing general anaesthesia for
non-related reasons (Broome et al. 2000).
In equine recurrent laryngeal neuropathy
(RLN), pathological changes in laryngeal adductor
muscle are more severe than abductor muscle
changes. As dysphonia is one <strong>of</strong> the earliest signs <strong>of</strong>
canine laryngeal paralysis, it may be that
preferential adductor compromise also occurs early
in the equivalent canine disease in dogs (Braund et
al. 1988b). Dogs with idiopathic laryngeal paralysis
however are generally not presented until the
advanced stages <strong>of</strong> the disease process, not being
subject to equivalent athletic demands <strong>of</strong> horses.
Idiopathic canine laryngeal paralysis is <strong>of</strong>ten
bilateral and usually affects middle aged to older
dogs (median age <strong>of</strong> 9.5 years in some clinical case
studies). This is in contrast to equine RLN, which is
primarily unilateral and usually diagnosed in
younger horses. As is the case with horses, it has
been suggested that male dogs are affected more
frequently with idiopathic laryngeal paralysis.
Clinical signs in acquired laryngeal paralysis are
similar to those <strong>of</strong> the congenital form, but usually
have a more gradual onset than the former. In
addition to altered or absent barking (dysphonia), a
s<strong>of</strong>t non-productive cough is also common in
affected dogs, which may be due to aspiration. Other
commonly recorded signs in severely affected dogs
include inspiratory stridor and dyspnoea during
exercise, excitement or hot weather; and even lifethreatening
respiratory obstruction (syncope) in
more severe cases. These signs are due to the
severity and frequent bilateral nature <strong>of</strong> the
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