Abnormal balance: vestibular and cerebellar disease

Question 1

What is the role of the vestibular system

Answer 1

sensory system
maintains balance
maintains appropriate position and movement of eyes, neck, trunk, limbs
detects head motion
regulated LMN innervating muscles in neck and body

Question 2

What CN receives vestibular hair cell receptor info?

Answer 2

CN VIII

Question 3

What do the utricle and saccule detect?

Answer 3

head position and linear acceleration

Question 4

What do the 3 semicircular ducts detect?

Answer 4

angular acceleration aka head rotation
when CNVIII is not equally activated on L and R

Question 5

What are the 5 efferent outputs of the vestibular system?

Answer 5

UMN spinal cord tracts
connections to brainstem nuclei of CNs III, IV and VI
cerebellum
cerebral cortex
vomiting center

Question 6

What is the effect of activating the vestibulospinal tracts?

Answer 6

increase ipsilateral extensor tone
decrease contralateral extensor ton

aka accomodated for weights shifts

Question 7

What is the effect of the vestibular system on the CN III, VI and IV?

Answer 7

enable coordinated conjugate eye movements in responses to changes in head position

Question 8

What is the physiological nystagmus?

Answer 8

eyes moving in a jerky fashion
eyes remain focused on original target but jerk in direction of the head movement to maintain a steady gaze while moving
= vestibulo-ocular reflex

Question 9

What is the afferent and efferent inputs for the vestibulo-ocular reflex?

Answer 9

afferent: CN VIII
info through brainstem
effrent: CN III, IV, VI

Question 10

What is the role of the the vestibulocerebellum?

Answer 10

flocculonodular lobe

recieved afferent input from vestibular nuclei
cerebellar efferent output is inhibitory to vestibular nuclei: releases GABA

Question 11

What is the role of the forebrain in the vestibular system?

Answer 11

axons travel from vestibular nuclei to contralateral vestibular cortex
enable conscious perception of balance and position

Question 12

How does disease affect the vestibular system?

Answer 12

at rest we have equal tonic input of L/R vestibular nuclei
head movement = unequal activation

when disease compromises one side = percieved as movement
reflex changes in posture and eye movement causing the clinical signs

Question 13

What are clinical signs of vestibular system dysfunction?

Answer 13

head tilt
abnormal balance: vestibular ataxia
tight circling
pathological nystagmus (when no head mvt)
abnormal vestibulo-ocular reflex
positional strabismus
nausea

Question 14

What does the head tilt tell us aout the vestibular system dysfunction?

Answer 14

towards the side of the lesion!
due to decreased extensor tone (least vestibular activity) on side of lesion/ increased tone on contralateral side

Question 15

What is the difference between a physiological and pathological nystagmus?

Answer 15

physiological: when head moved
pathological: at rest due to disrupted vestibular input
(fast phase away from lesion)

Question 16

What is a positional strabismus?

Answer 16

abnormal eye position
raising the head results in ventrolateral deviation of eye on affected side

Question 17

What are types of peripheral lesion of vestibular system?

Answer 17

compromise CN VII
sympathetic innervation to eye
close to tympanic bulla

Question 18

What are types of central lesions affecting vestibular system?

Answer 18

other CN nuclei
ascending proprioceptive tracts from spinal cord (proprioceptive ataxia)
descending UMN tracts (tetraparesis)
ascending reticular activating system (abnormal mentation)
LOOK FOR brainstem dysfunction signs

Question 19

What are clinical signs only seen in central vestibular disease?

Answer 19

vertical nystagmus
nystagmus chages direction with changes in head position
possible proprioceptive deficits and/or paresis

Question 20

What is the difference in consciousness in central vs peripheral vestibular disease?

Answer 20

central: obtunded, stuporous, comatose
peripheral: normal, disorientated

Question 21

What is the treatment and prognosis for idiopathic vestibular disease?

Answer 21

peracute onset, no central involvment, typically older dogs

tx: supportive - antiemetics, IVFT, nursing care and hand feeding

prognosis: good, possible residual head tilt

Question 22

What is the function of the cerebellum?

Answer 22

regulate rate, range and forve of movemnt

coordinates movement
ensures appropriate posture
maintains equilibrium

afferent and efferent info stays ipsilateral

Question 23

What is the afferent and efferent path of cerebellum function?

Answer 23

receives proprioceptive info from muscl spinfles, golgi tendon organs, vestibular system (informed by head and body)

receives info from motor cortex in forebrain on intended movements

modulates motor activity: ensures appropriate posture and desired movement of appropriate rate range and force

Question 24

What are some signs of cerebellar dysfunction?

Answer 24

cerebellar ataxia
truncal ataxia/sway
wide based stance
hypertonus (spasticity)
decerebellate posture
intention tremor
abnormal menace response

• unilateral lesion = ipsilateral clinical signs

if lesion of vestibylocerebellum: vestibular ataxia, head tilt, positional and pathological strabismus

Question 25

What is dysmetria?

Answer 25

inability to regulate rate range and force of movement

Question 26

What is hypermetria?

Answer 26

form of dysmetria

increased rate = sudden jerky movements
increased range = large exagerated movements that overreach intended goal
increased force = forceful movements of exaggerated strength

look like soldiers marching

Question 27

What is hypertonia?

Answer 27

increased muscle tone due to loss of inhibition of UMNs of muscle spindles

Question 28

What are clinical signs of lesions in the rostral lobe of the cerebellum?

Answer 28

particularly inhibitory to UMNs
can caused marked rigid extension of thoracic limbs and opisthotonus
hypertonia of hip flexors = pelvic limbs flexed under body

AKA decerebellate posture

Question 29

What is the mentation in decerebellate posture?

Answer 29

normal because no involvement of forebrain

Question 30

How doesWhat is paradoxical vestibular disease?

Answer 30

increased extensor tone on lesion side
head tilt, leaning/falling on opposite side of lesion
fast phase of nystagmus is towards lesion

cerebellum suppresses vestibular nuclei activation of extensor muscles and lesion = less inhbition of vestibular nuclei causing more activity in the nuclei on the side of the lesion = brain perceives this as animal turning towards lesion

Question 31

How can you recognise paradoxical vestibular lesion?

Answer 31

look for lateralised cerebellar deficits
look for delayed postural reactions in ipsilateral limbs

so on the side of lesion is side with postural deficits and/or cerebellar signs
opposite to lesion is head tilt

Question 32

What is cerebellar cortical degeneration?

Answer 32

postnatal degeneration largely affecting cerebellar cortex/grey matter

symmetrical progressive cerebellar ataxia

no tx available = euth.

Question 33

What is neospora caninum?

Answer 33

intracellular protozoan parasite
can cause severe diffuse cerebellitis with secondary cerebellar atrophy, myositis

Question 34

What is tx for neospora caninum

Answer 34

clindamycin
+/- trim. sulph