Page 662 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.2 Surgical conditions of the respir atory tr act 637

VetBooks.ir Management case signs of DDSP may be noticed, often combined
with low-grade dysphagia, typically nasal discharge
Permanent pharyngeal collapse requires treatment
of the underlying condition, such as drainage of gut-
scopic examination. Careful assessment of the pala-
tural pouch empyema, drainage of retropharyngeal containing food material. Diagnosis requires endo-
abscesses (such as caused by strangles) or relief of tal seal around the epiglottis is required and small
guttural pouch tympany. If this cannot be readily defects can be missed. Smaller defects can be man-
achieved, then consideration should be given to tra- aged conservatively as attempts to reduce the defect
cheotomy. Dynamic dorsal or lateral pharyngeal col- surgically are usually unsuccessful.
lapse does not have a specific treatment. Generally,
treatment with rest and anti-inflammatory medica- RECURRENT LARYNGEAL NEUROPATHY
tions is provided. Collapse of the ventral nasophar-
ynx can be treated in the same way as DDSP, with Definition/overview
similarly unpredictable results. Recurrent laryngeal neuropathy (RLN) is probably
the most important cause of upper airway obstruc-
Prognosis tion in the horse. It has been recognised for centuries
Permanent pharyngeal collapse caused by a treat- and remains a major cause of economic loss to the
able condition has an excellent prognosis. Once the horse industry. Equine idiopathic RLN is associated
swelling has resolved there appears to be no long- with the length of the recurrent laryngeal nerve, and
term ‘stretching’ or other distortion of the pharynx. hence is more frequent in large horses. The left side
Dynamic dorsal and lateral pharyngeal collapse is of the larynx is almost invariably affected, as the left
anecdotally presumed to have a good prognosis, with nerve is longer.
most horses improving with increased maturity and There are several causes of RLN and it is impor-
resolution of inflammation. No detailed case studies tant not to overlook these in the rush to diagnose
are available, and it has been suggested that this good idiopathic RLN. Other causes include infections
prognosis may be slightly optimistic. Ventral pha- such as guttural pouch mycosis or equine protozoal
ryngeal collapse has a prognosis similar to DDSP. myelopathy, trauma, including perivascular injection
There is little evidence that the surgical attempts to of irritant substances (during jugular vein injection)
stiffen the palate are of any benefit, despite appear- and toxicoses (including lead and organophosphates).
ing logical. Equine idiopathic RLN is a common condition in
all large breeds of horses. Microscopically the disease
CLEFT PALATE AND is present in all horses and clinical signs are frequent
PALATAL HYPOPLASIA in all types of performance horse. The spectrum of
the disease varies enormously. Some horses showing
(See also Chapter 4.1, p. 756.) asymmetry of the rima glottidis at rest will show no
further collapse of the arytenoid cartilages during
Definition/overview dynamic endoscopy, while other horses that appear
Cleft palate is a well-recognised congenital defor- mildly afflicted at rest will develop marked collapse
mity, but the condition is rare in the horse. Cleft associated with severe respiratory stertor and poor
palate can involve the hard palate as well as the soft performance at exercise.
palate. Possibly because of its use as an athlete, and
the intranarial larynx, hypoplasia of the soft palate Aetiology/pathophysiology
is recognised more commonly in the horse than in RLN is a pathological diagnosis. The conditions
other species. Hypoplasia usually presents as small listed above will each cause neural damage accord-
oval defects from the free border. Cleft palate in the ing to their specific pathology: for instance, gut-
foal is covered elsewhere (p. 756). Smaller defects tural pouch mycosis will cause fungal erosion of
may be overlooked in a young animal and may not the nerve, with associated swelling and inflamma-
be noticed until a horse starts to exercise, in which tion. Idiopathic equine RLN is a distal axonopathy.