Principles of Ataxia Flashcards
What is hypometria?
Shortened protraction phase of gait
What is ataxia?
Neurological signs consisting of gross incoordination of muscle movements
What is hypermetria?
Longer protraction phase of gait
What is dysmetria?
Impairment of the ability to control the distance, power and speed of an action
Where is sensory ataxia localised to?
General proprioceptive pathways which are the peripheral nerve, dorsal root, spinal cord, brainstem and forebrain
What are the clinical signs associated with sensory ataxia?
Abnormal postural reactions and limb paresis
Where is vestibular ataxia localised to?
Vestibular apparatus including the vestibular nuclei, vestibular portion of CN VIII and vestibular receptors
What are the clinical signs associated with vestibular ataxia?
Head tilt, leaning/falling/rolling to one side, abnormal nystagmus, positional strabismus and normal/abnormal postural reactions
Where is cerebellar ataxia localised to?
Cerebellum
What are the clinical signs associated with cerebellar ataxia?
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
What makes up the vestibular system?
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
How do you test the vestibular system?
Oculovestibular reflex = slow flicking of the eyes when turning the head so vision doesn’t blur
What is the pathway of the oculovestibular reflex?
Hair cells -> vestibular receptors -> vestibular nuclei -> oculomotor nerve/abducens nerve -> left medial rectus/right lateral rectus
Why do extensor muscles lose tone in vestibular disease?
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
What are the inputs into the vestibular system?
Head motion and angular acceleration from the semicircular canals
Head position and gravity from the saccule and utricle
Visual, proprioceptive and tactile inputs
What are the outputs of the vestibular system?
Forebrain for perceived orientation
Spinal cord and cerebellum
Oculomotor system and eye movements
What are some other inputs to the vestibular nuclei?
Inhibitory from the cerebellum, spinal cord, pontine reticular formation and contralateral vestibular nuclei
What is a head tilt defined as clinically?
One ear is held lower than the other
What is a head turn defined as clinically?
Head is turned towards the body in the median plane
What is pendular nystagmus?
What diseases is it seen with?
Congenital abnormality due to a larger number of fibres crossing chiasma
Cerebellar disorders and visual deficits or in Siamese/Birmen/Himalayan cats
What is jerk nystagmus? What are the different types? What does the slow phase indicate?
Sign of vestibular disease and is either horizontal, vertical or rotary
Slow phase is always towards the side of the lesion
What causes positional strabismus?
Lack of innervation/incorrect innervation to the extraocular muscles
What are the clinical signs of a central vestibular lesion?
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
What are the clinical signs of peripheral vestibular disease?
Alert but disorientation possible
Cranial nerve VII only affected
Horner’s syndrome is possible
Horizontal and rotary nystagmus
What do you need to ask if an animal has peripheral nystagmus?
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
What is the presentation of bilateral vestibular disease?
No nystagmus, no oculovestibular response, head swaying from left to right
What is Horner’s syndrome?
Loss of sympathetic innervation to the eye resulting in enophthalamus, third eyelid protrusion, ptosis, miosis and congested vessels
What does Horner’s syndrome look like in horses?
Ptosis, miosis, enophthalamus, prominent third eyelid, conjunctival and nasal hyperaemia, sweating
What are the three functional parts of the cerebellum?
Vestibulo-cerebellum
Spino-cerebellum
Cerebro-cerebellum
What is the function of the cerebellum?
To maintain equilibrium
Regulate muscle tone to preserve normal position at rest or whilst moving
To coordinate movement
What are the clinical signs of paradoxical vestibular ataxia?
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
What is paradoxical vestibular ataxia linked to?
The caudal cerebellar peduncle in the paraflocculonodular lobe of the cerebellum
What does paradoxical vestibular ataxia result from?
Loss of inhibition to vestibular nuclei so there is increased tone in the extensor muscles resulting in a head tilt away from the lesion
How to clinical signs of cerebellar ataxia help you localise the lesion?
Principle clinical signs are linked to the cerebellar area affected
What are the principle signs associated with rostral cerebellar ataxia?
Opisthotoms
Forelimb hyperextension
Hindlimb hip flexion (extension if lesion includes ventral part of vermis)
What are the principle signs associated with caudal cerebellar ataxia?
Hypotonia
Hypermetria
Intention tremor
What are the clinical signs associated with flocculonodular cerebellar ataxia?
Dysequilibrium
Drunken, broad-based staggering gait
Loss of balance
Abnormal nystagmus
What are the clinical signs associated with caudal cerebellar peduncle cerebellar ataxia?
Paradoxical vestibular signs
What are the clinical signs of cerebellar ataxia if the fastigial and interpositional nuclei are affected?
Dilated pupil
3rd eyelid protrusion
Enlarged palpebral fissure
What is cerebellar syndrome?
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
