What is the function of the vestibular system?
coordinate eye movements with head movement
-senses head movement and correlates the movement of the eyes to match
What are the anatomic components of the vestibular system?
*central:
-brain stem
-cerebellum
*peripheral:
-inner ear
-cranial nerve 8
How does the vestibular system maintain posture?
senses movement and activates or inhibits muscles to maintain posture
What should be done when a central vestibular lesion is suspected?
*look for other signs of brainstem lesion:
-vestibular system in the brain is small; it is unlikely to be the only component affected
What are the characteristics of a head tilt?
-one ear is lower than the other
-indicates vestibular disease
-does not distinguish central vs peripheral lesion
Why is it important to distinguish head tilt from head turn?
head turn indicates forebrain lesion instead of vestibular disease
How does the direction of the head tilt differ between central and peripheral lesions?
peripheral: head tilts towards the lesion
central: head can tilt in either direction
Why is it important to assess vestibular patients for ataxia/weakness?
only central vestibular lesions cause postural deficits; helps to localize
What are the characteristics of jerk nystagmus?
-has fast and slow phases
-normal response to spinning
-jerk nystagmus + still head means the vestibular system thinks patient is spinning
What are the types of nystagmus?
*physiologic/rotation-induced
-normal
*spontaneous
-abnormal
-indicates vestibular dz
*positional (head in abnormal position but not moving)
-abnormal
-indicates vestibular dz
Why does vestibular disease cause nystagmus?
the brain compensates for vestibular deficits early on
How does nystagmus differ between a central vestibular lesion and a peripheral vestibular lesion?
*peripheral:
-horizontal and/or rotary movement
-fast phase away from the side of the lesion
-non-changing
*central:
-any direction including vertical
-often changes direction with head position
What are the characteristics of pendular nystagmus?
-equal speed in each direction
-congenital in oriental breed cats and dairy cattle
What are the characteristics of strabismus?
-deviation of the eye
-ventral strabismus can occur with vestibular disease
-usually occurs on the same side as the lesion
What are the characteristics of facial nerve paralysis?
-can occur with central or peripheral lesions
-CN7 is affected with ear disease
-other cranial nerves being effected indicates brainstem location
What are the characteristics of horner’s syndrome?
-loss of sympathetic innervation to face
-occurs with peripheral lesions; nerve passes by inner ear
-patients present with small pupil, drooping upper lid, protruding 3rd eyelid, and enophthalmos
What are the characteristics of vestibular compensation?
-reason why we see improvement in vestibular dz cases
-brain relies on somatosensory cues (proprioception, vision)
-facilitated by movement; important to get patients moving as quickly as possible
-inhibited by drugs that suppress vestibular system; only use as needed
What are the characteristics of otitis media-interna?
-most commonly caused by Staph.
-usually an extension from untreated otitis externa that gets through the ear drum
What are the signs of otitis media-interna?
-shaking head
-yawning
-facial paralysis
-horner’s syndrome
Which diagnostics are done in cases of otitis media-interna?
-otoscopic examination
-radiographs
Which radiographic view is best for identifying thickened tympanic bullae walls?
VD view with the mouth open
What is the treatment for otitis media-interna?
-4 to 6 weeks of systemic antibiotics
-culture/sensitivity preferred; typically treated with cephalexin
-surgery to remove gunk +/- ablate if severe
What are the characteristics of canine idiopathic vestibular syndrome?
-old dogs; mean of 12.5 years
-sudden onset
-no facial paralysis or horner’s syndrome
-often misdiagnosed as stroke or brain tumor
-improve spontaneously
What are the characteristics of feline idiopathic vestibular syndrome?
-any age cat
-warmer months
-sudden onset of ataxia, nystagmus, and head tilt
-no facial paralysis, horner’s, or postural reaction deficits
-improve spontaneously within several weeks
-no evidence that steroids or antibiotics are effective
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