Principles of Ataxia

Question 0

What is hypometria?

Answer 0

Shortened protraction phase of gait

Question 1

What is ataxia?

Answer 1

Neurological signs consisting of gross incoordination of muscle movements

Question 2

What is hypermetria?

Answer 2

Longer protraction phase of gait

Question 3

What is dysmetria?

Answer 3

Impairment of the ability to control the distance, power and speed of an action

Question 4

Where is sensory ataxia localised to?

Answer 4

General proprioceptive pathways which are the peripheral nerve, dorsal root, spinal cord, brainstem and forebrain

Question 5

What are the clinical signs associated with sensory ataxia?

Answer 5

Abnormal postural reactions and limb paresis

Question 6

Where is vestibular ataxia localised to?

Answer 6

Vestibular apparatus including the vestibular nuclei, vestibular portion of CN VIII and vestibular receptors

Question 7

What are the clinical signs associated with vestibular ataxia?

Answer 7

Head tilt, leaning/falling/rolling to one side, abnormal nystagmus, positional strabismus and normal/abnormal postural reactions

Question 8

Where is cerebellar ataxia localised to?

Answer 8

Cerebellum

Question 9

What are the clinical signs associated with cerebellar ataxia?

Answer 9

Wide-based stance, intention tremors, loss of balance, truncal sway, delayed onset and hypermetric hopping, ipsilateral menace deficits with normal vision, no limb paresis or conscious proprioception deficits and pendular nystagmus

Question 10

What makes up the vestibular system?

Answer 10

Semi-circular canals in the ear contain vestibular hair cells with vestibular receptors that either depolarise or hyperpolarise depending in which way the hairs move resulting in feedback on velocity and gravity to the vestibular nuclei centrally

Question 11

How do you test the vestibular system?

Answer 11

Oculovestibular reflex = slow flicking of the eyes when turning the head so vision doesn’t blur

Question 12

What is the pathway of the oculovestibular reflex?

Answer 12

Hair cells -> vestibular receptors -> vestibular nuclei -> oculomotor nerve/abducens nerve -> left medial rectus/right lateral rectus

Question 13

Why do extensor muscles lose tone in vestibular disease?

Answer 13

Vestibular system accounts for extensor muscles on the same side so if there is a lesion there is a loss of tine of extensor muscles on that side of the body so that side drops

Question 14

What are the inputs into the vestibular system?

Answer 14

Head motion and angular acceleration from the semicircular canals
Head position and gravity from the saccule and utricle
Visual, proprioceptive and tactile inputs

Question 15

What are the outputs of the vestibular system?

Answer 15

Forebrain for perceived orientation
Spinal cord and cerebellum
Oculomotor system and eye movements

Question 16

What are some other inputs to the vestibular nuclei?

Answer 16

Inhibitory from the cerebellum, spinal cord, pontine reticular formation and contralateral vestibular nuclei

Question 17

What is a head tilt defined as clinically?

Answer 17

One ear is held lower than the other

Question 18

What is a head turn defined as clinically?

Answer 18

Head is turned towards the body in the median plane

Question 19

What is pendular nystagmus?

What diseases is it seen with?

Answer 19

Congenital abnormality due to a larger number of fibres crossing chiasma
Cerebellar disorders and visual deficits or in Siamese/Birmen/Himalayan cats

Question 20

What is jerk nystagmus? What are the different types? What does the slow phase indicate?

Answer 20

Sign of vestibular disease and is either horizontal, vertical or rotary
Slow phase is always towards the side of the lesion

Question 21

What causes positional strabismus?

Answer 21

Lack of innervation/incorrect innervation to the extraocular muscles

Question 22

What are the clinical signs of a central vestibular lesion?

Answer 22

Possible paresis and conscious proprioceptive losses
Normal/obtunded/stupourous/comatose
Cranial nerves V-XII may be affected
Horner’s syndrome rare
Horizontal, rotary and vertical nystagmus
Nystagmus changes with head position

Question 23

What are the clinical signs of peripheral vestibular disease?

Answer 23

Alert but disorientation possible
Cranial nerve VII only affected
Horner’s syndrome is possible
Horizontal and rotary nystagmus

Question 24

What do you need to ask if an animal has peripheral nystagmus?

Answer 24

``` Are they on ototoxic drugs? If so does it improve when stopped? If not perform otoscopic exam - if normal = idiopathic - if abnormal = myringotomy - suppurative = otitis media/interna so antibiotics, no bacteria = MRI/CT = neoplasia/polyp/trauma ```

Question 25

What is the presentation of bilateral vestibular disease?

Answer 25

No nystagmus, no oculovestibular response, head swaying from left to right

Question 26

What is Horner's syndrome?

Answer 26

Loss of sympathetic innervation to the eye resulting in enophthalamus, third eyelid protrusion, ptosis, miosis and congested vessels

Question 27

What does Horner's syndrome look like in horses?

Answer 27

Ptosis, miosis, enophthalamus, prominent third eyelid, conjunctival and nasal hyperaemia, sweating

Question 28

What are the three functional parts of the cerebellum?

Answer 28

Vestibulo-cerebellum Spino-cerebellum Cerebro-cerebellum

Question 29

What is the function of the cerebellum?

Answer 29

To maintain equilibrium Regulate muscle tone to preserve normal position at rest or whilst moving To coordinate movement

Question 30

What are the clinical signs of paradoxical vestibular ataxia?

Answer 30

Possible paresis, opposite side head tilt, normal/obtunded/stuporous/comatose mentation, CNs V-XII possibly affected, rarely Horner's, horizontal/rotary/vertical nystagmus, nystagmus that changes with head position

Question 31

What is paradoxical vestibular ataxia linked to?

Answer 31

The caudal cerebellar peduncle in the paraflocculonodular lobe of the cerebellum

Question 32

What does paradoxical vestibular ataxia result from?

Answer 32

Loss of inhibition to vestibular nuclei so there is increased tone in the extensor muscles resulting in a head tilt away from the lesion

Question 33

How to clinical signs of cerebellar ataxia help you localise the lesion?

Answer 33

Principle clinical signs are linked to the cerebellar area affected

Question 34

What are the principle signs associated with rostral cerebellar ataxia?

Answer 34

Opisthotoms Forelimb hyperextension Hindlimb hip flexion (extension if lesion includes ventral part of vermis)

Question 35

What are the principle signs associated with caudal cerebellar ataxia?

Answer 35

Hypotonia Hypermetria Intention tremor

Question 36

What are the clinical signs associated with flocculonodular cerebellar ataxia?

Answer 36

Dysequilibrium Drunken, broad-based staggering gait Loss of balance Abnormal nystagmus

Question 37

What are the clinical signs associated with caudal cerebellar peduncle cerebellar ataxia?

Answer 37

Paradoxical vestibular signs

Question 38

What are the clinical signs of cerebellar ataxia if the fastigial and interpositional nuclei are affected?

Answer 38

Dilated pupil 3rd eyelid protrusion Enlarged palpebral fissure

Question 39

What is cerebellar syndrome?

Answer 39

Spastic, dysmetric or hypermetric ataxia Intention tremor Ipsilateral menace deficit and normal vision Broad-based stance Postural reactions delayed with exaggerated responses +/- anisocoria, opisthotamus and vestibular signs