Page 846 - Problem-Based Feline Medicine

838 PART 10 CAT WITH SIGNS OF NEUROLOGICAL DISEASE

Horner’s syndrome, partial or complete. The postural reaction deficits ipsilateral to the lesion but
cochlear part of the vestibulo-cochlear nerve may contralateral to the head tilt.
be affected leading to ipsilateral deafness.
● If the disease is bilateral, there is no head tilt or
only a mild one on the side that is the most
WHERE?
severely affected. The more acute the disease, the
more severe the disorientation. The cat is reluc- Peripheral vestibular disease results from a problem
tant to walk and has a crouched posture, low to in the petrosal bone or tympanic bulla.
the ground. The head characteristically moves ● The peripheral part of the vestibular apparatus
from side to side in exaggerated motions and (receptors and nerve) is situated in the inner ear,
there is often ventroflexion of the head and neck. in close proximity to the middle ear. The inner and
The physiological nystagmus (normal involuntary middle ear are located within the petrosal bone or
rhythmic typewriter-like movements of the eyes tympanic bulla. The facial nerve, the parasympa-
initiated by side-to-side movements of the head) thetic innervation of the lacrimal glands and
is poor to absent. the sympathetic nerve for pupillary dilatation
are the neurological structures associated with the
Central vestibular disease:
middle ear.
● The most consistent feature indicating central
● Diseases of the inner ear can by extension reach the
vestibular disease is the concomitant presence
middle ear and vice versa.
of somnolence, or quietness of the animal. This
● The neurologic structures of the middle ear are
may or may not be obvious at time of exami-
more resilient to insult than the receptors in the
nation, but will be evident with good history
inner ear (receptors vs axons). As a result, middle
taking.
ear disease may be present without neurological
● The head tilt is toward the side of the lesion. The
deficits. With time, facial paresis/paralysis and/or
nystagmus is horizontal, rotatory or vertical and
Horner’s syndrome may appear.
may change in direction.
● The auditory receptors are situated in the inner
● Due to their close proximity, other central nerv-
ear as well. Unilateral deafness goes unnoticed
ous system structures may be involved ipsilater-
clinically but is diagnosed with electrodiagnostic
ally. These include the ascending reticular
testing (brain auditory-evoked potentials).
activating system or ARAS (somnolence) and the
ipsilateral trigeminal nerve (loss of facial sensation Central vestibular disease results from an intracranial
and/or masticatory muscle atrophy), abducent nerve problem in the brainstem, at the level of the rostral
(strabismus), facial nerve (facial paresis/paraly- medulla. This area is in close proximity to the cerebel-
sis), cerebellum (tremors, hypermetria), ascend- lum and pons. This anatomical location is called the
ing sensory pathways (proprioceptive deficits) and cerebello-ponto-medullary angle.
descending motor pathways (upper motor neuron
weakness).
WHAT?
● Bilateral involvement of the central vestibular
system appears clinically similar to bilateral The most common causes of vestibular disease are
peripheral vestibular disorders in the early phase, peripheral and include:
except that the animal is more quiet or somnolent. ● Idiopathic vestibular disease.
If the cause is not corrected, involvement of other ● Otitis media-interna.
structures of the brainstem and/or cerebellum ● Less common causes are the middle ear polyps and
ensues. tumors.
Paradoxical vestibular syndrome. Central vestibular diseases are not as frequent as
● In this rare syndrome of central vestibular disease, peripheral diseases.
the head tilt is contralateral to the lesion. The diag- ● Inflammatory diseases are the most common, with
nosis is made on the presence of cerebellar signs or the clinical signs directly related to the location and