Page 1075 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1050 CHAPTER 10

VetBooks.ir slapped and the dorsal larynx palpated. The normal function of multiple CNs is Horner’s syndrome.
The most well-known syndrome affecting the
response is for the contralateral arytenoid cartilage
to abduct briefly, which is palpated as a quick twitch
the sympathetic supply to the ocular structures and
of the laryngeal musculature. The signs of this syndrome are related to damage to
The afferent pathway is via segmental spinal other structures innervated by sympathetic nerves
nerves, cranially via the contralateral cervical spinal in the head and neck. The signs are ipsilateral to the
cord white matter, and finally the contralateral vagus lesion and include excessive sweating of the head
nuclei in the medulla oblongata. The efferent path- and neck, drooping of the eyelid, constriction of
way is from the vagus nerve, through the thorax, and the pupil, protrusion of the nictitating membrane
back up the neck via the recurrent laryngeal nerve to and enophthalmos. Horner’s syndrome signs may
the larynx. The slap test reflex could be interrupted be due to a lesion anywhere in the cervical sym-
along any part of the afferent or efferent pathway. pathetic trunk: common lesions include damage to
the brachial plexus, space- occupying lesions of the
Accessory nerve (CN XI) neck, perivascular injection near the jugular, gut-
Lesions of this nerve are rare, and cause paralysis of tural pouch disease, basilar skull fractures and ret-
the trapezius and sternocephalicus muscles (part of robulbar masses. More rarely, Horner’s syndrome
the triad of neck strap muscles). Denervation atrophy may be due to damage along the descending sym-
of these muscles might be detected clinically where pathetic tracts in the brainstem, or damage to the
an abnormality of the accessory nerve is present. cervical and cranial thoracic spinal cord.

Hypoglossal nerve (CN XII) PHASE 5 – NECK AND
This nerve innervates the tongue, and lesions result TRUNK EXAMINATION
in paralysis. Unilateral dysfunction results in tongue
muscle atrophy and weak retraction of the tongue This phase begins with a check over the whole body
when pulled out of the side of the mouth. Bilateral for evidence of muscle atrophy. The neck should be
lesions result in tongue protrusion, problems with examined in detail (see Chapter 1.7a) for symme-
mastication and swallowing, and inability to with- try, swellings, localised sweating and normal range
draw the tongue back into the mouth when pro- of movement (Fig. 10.8). The whole horse is then
truded. As mentioned above in the glossopharyngeal checked for skin sensation (Fig. 10.9) and those spi-
nerve section, severe cerebral lesions (supranuclear nal reflexes that can be tested in the standing adult
palsy) may result in tongue protrusion and slow horse. The aim of these tests is to check the function
retraction due to impaired voluntary control. In of segments of the grey matter of the spinal cord and
these cases, however, there is no atrophy and the peripheral nerve function.
tongue will eventually be retracted if the horse is Skin sensation over the neck is checked with a
stimulated sufficiently. blunt instrument that is tapped on the skin. The
horse should respond with signs of conscious per-
Syndromes of cranial nerve disease ception (turning towards the stimulus) and a skin
In general terms, CN damage can result from a twitch. When this is performed on the neck, there
lesion in the brainstem nuclei or the peripheral should be a cervicofacial reflex which involves an
nerves. Brainstem lesions tend to result in weakness ipsilateral ear twitch, eyelid closure and contracture
or depression. Peripheral nerve lesions may affect of the lip commissure. The pathway of the cervico-
several nerves owing to their juxtaposition. These facial reflex is not entirely understood.
include CNs III, IV and VI, which can be damaged Over the trunk, skin sensation and spinal reflexes
by fractures of the base of the skull, CNs VII and are checked by tapping a blunt instrument over the
VIII with inner ear disease or temporohyoid oste- thorax and watching for a response in the cutaneous
opathy, CNs IX and X with guttural pouch disease muscle. Extension of the thoracolumbar vertebral col-
and CNs II and V with sphenopalatine sinus disease. umn can be assessed by running the blunt instrument