Movement disorders

Question 1

Define Dystonia

Answer 1

Dystonia = sustained slow muscle contractions of agonist and antagonist muscles of a body region
–> suggests b/d of the normal reciprocal innervation between opposing muscles

Often initiated or worsened by voluntary movement, and patterned twisting

DDX spasticity from loss of UMN inhibition

Question 2

Types of peripheral nerve hyperexcitability (7)

Answer 2

Paroxysmal Dyskinesias

Myokymia

Fasciculations

Cramps

Myotonia

Neuromyotonia

Tetany

Question 3

Importance of basal nuclei/ganglia

Answer 3

Major role in the gating of movement

Includes several regions in the middle of brain, a group of subcortical interconnected structures

5 cortico-BN-thalamo-cortical loops are a complex neuronal circuitry
(motor, oculomotor, associative, limbic and orbitofrontal)

Question 4

Importance of caudate- putatem

Answer 4

Overriding modulatory control of the basal nuclei

–> D1 R activation increases glutaminergic activity

–> D2 R activity decreases glutaminergic activity

Question 4

Components of basal ganglia

Answer 4

Caudate nucleus
Putamen
(together those are striatum)
Globus pallidus (internal and external)
Subthalamic nucleus
Substantia nigra

Question 5

Steps of DIRECT movement pathway and main function

Answer 5

Main function is the disinhibition of the thalamus allowing for initiation of voluntary movement

PATHWAY: MSIT
motor cortex
–> excitatory signal to the caudate putamen(striatum) which activates D1 R

–> inhibitory projections from striatum to the substantia niagra pars reticulata

–> stops the tonic inhibitory GABA projections to thalamus

–> disinhibition of the thalamus

Question 6

Steps of INDIRECT Movement pathway and its main function

Answer 6

Main function is the inhibition of movement through enhancing substantia niagra pars reticulata output to thalamus

PATHWAY: MSENIT
Motor cortex projections to the caudate-putamen (striatum)

–> Inhibitory projections from striatum to globus pallidus externus this time

–> inhibitory projections to the subthalamic nuclei

–> Excitatory stimulus to substantia niagra pars reticulata

–> promotes inhibition of thalamus and thus stopping movement.

Question 7

Dopamine role in movement pathways

Answer 7

Most of the projections are glutamte/GABA for excitatory and inhibitory

But dopamine receptors in the caudate putatem (striatum)can activate the direct pathway (via D1 R) and inhibit the indirect pathway (via D2 R)

Dopamine comes from pars compacta of the substantia niagra

Question 8

What is chorea

Answer 8

abrupt (jerky), non-patterned and un-sustained low amplitude contraction of muscle groups

Question 9

What is dyskinesia

Answer 9

Dyskinesia = self limiting, episodic, involuntary movements that are recurrent

Question 10

What is athetosis

Answer 10

Prolonged slow involuntary contraction of the trunk muscles –> nonrhythmic bending and writhing movements

–> prevents stable maintenance of posture

Question 11

What is ballism

Answer 11

Abrupt involuntary contraction of the proximal limb muscles
–> large amplitude flailing or flinging movements

Fits with what is often seen in paroxysmal dyskinesias
But difficult to differentiate in dogs from chorea and athetosis so all together are termed dyskineasias.

Question 12

What is myokymia

Answer 12

focal or generalised continuous contraction of the facial or limb myofibres.
Often has undulating or verminous quality.

May be seen with spinocerebellar ataxia degenerative syndromes in hereditary ataxias.
–> progress to generalised stiffness and collapse with hyperthermia

–> EMG findings of myokymic or neuromyotonic discharges which are short rhythmic bursts

persists with sleep and GA but blocked by neuromuscular blocking agents

Question 13

What is myoclonus

Answer 13

Brief shock like contractions of skeletal muscle due to sudden involuntary contraction followed by relaxation

Often repeated contractions that result in movement of a body part involuntarily (unlike tremors or myokymia or myotonia where there is not a movement of body part.

Can occur at rest and then worsen with stimulus

Question 14

What is myotonia and neuromyotonia

Answer 14

Disturbance in relaxation after voluntary contraction or percussion

in neuromyotonia there is persistent muscle stiffness and delayed relaxation due to abnormal motor neuron discharges

persists with sleep and GA but blocked by neuromuscular blocking agents

Question 15

What are fasciculations

Answer 15

Brief spontaneous contraction of a small muscle group, no limb or body movement

Question 16

What is tetany

Answer 16

Sustained muscle contraction usually involving extensor muscles

Question 17

What are tremors and what types are there

Answer 17

involuntary rhythmic oscillatory movements of a body part with symmetric velocity in both directions

Can be at rest, postural, action or intention

May be physiological or pathological

Question 18

General approach to movement disorders JVIM 2022 ECVN consensus

Answer 18

Define if hyper or hypokinetic

Paroxysmal or persistent

Exercise induced or not

Detailed clinical description of movements (uni/bi-lateral, proximal/distal, rhythmic/irregular,triggers

Is it consistent with a movement disorder - should be painless, involuntary and may be episodic or occur continuously (dystonia)

Is their a known inherited condition in the affected breed
Or could this be acquired (drug administration)

Question 19

Difference b/w hyper and hypokinetic disorders

Answer 19

Hyper - functional disturbance anywhere in the basal nuclei, spinal cord, peripheral nervous system or cerebral cortex
Includes dyskinesias, dystonias, myoclonus and tremors

HYpo - difficulty initiating movement. Only seen in multiple system degeneration of Kerry blue terriers and Chinese crested dogs.

These signs would be attributed to the degeneration of the substantia nigra as well as caudate nucleus

Question 20

Possible causes of acquired paroxysmal dyskinesias

Answer 20

Propofol - dystonia

Phenobarbital - dyskinesia

Structural intracranial lesions

Paroxysmal gluten sensitive dyskinesia of Border Terriers

Tetanus toxicity

Question 21

Paroxysmal dyskinesias in dogs that have genetic test and other breeds affected

Answer 21

Genetic test

• Multiple system degeneration - Kerry terrier and Chinese crested. (Auto recessive)
• CKCS Episodic falling syndrome (Auto recessive)
• SCWT PDK (Auto recessive)
• Shetland sheepdog (Auto dom)

No test:
Border Terrier - can also get acquired form from gluten hypersensitivity
Scottie Cramps
Labrador Hypertonicity
JRT, Boxer, Maltese and GSP paroxysmal dyskinesias

Question 22

Peripheral nerve hyperexcitability disorders cause and symptoms

Answer 22

Wide group of CNS/PNS disorders mostly involving defects in K+ channels (hereditary or immune mediated) or demyelination causing reorganisation of K+ channels

Can cause:
Myokymia - rhythmic focal or generalised muscle contraction (think spinocerebellar dz in JRT)

Myotonia (sustained contraction seen in Mini schauzer myotonia congenita and hyperkalaemic periodic paralysis)

Neuromyotonia - (severe myokymia with persistent stiffness and delayed relaxation)

Cramps - sudden severe contraction, rarely reported may be associated with Addison’s

Fasciculations - (often benign but can indicate neuropathy)

Tetany (sustained contraction due to disinhibition of LMN)
Neuromyotonia

Question 23

Definition of and types of Tremor

Answer 23

Rhythmic bursts of motor unit activity, can be of variable amplitude but regular frequency. Can be focal or generalised.

ACTION TREMORS
If occurring with movement (kinetic) then usually indicative of cerebellar disease

Postural tremors that occur when standing or when stressed dissipate with movement or at rest

Can also be caused by mycotoxins which cause persistent tremors at rest and exacerbated by effort

Question 24

Type of myoclonus (3) and a couple of differentials

Answer 24

Physiologic - hypnic jerk; hiccups

Epileptic - observed or EEG recorded epileptic event during myoclonus.
Associated with Lafora dz (Beagle, Wirehaired Dachshund), neuronal ceroid lipofucinosis
Feline auditory seizures

Non-epileptic: CDV, Startle dz (Irish Wolfhound), Hemifacial spasms
May be that these just havent progressed to seizures yet

Previously classified by CNS region: cortical ; subcortical (associated with auditory stimulation); and peripheral (due to nere compression)

Question 25

Diagnostic approach to movement disorders

Answer 25

Given the possibility of implication of the basal nuclei in the pathogenesis of PxD and myoclonus and isolated dystonia a work up as outline for that of canine IE would be indicated.

Consider diseases with clinical signs similar to dystonia: vestibular disorders or lameness causing limb to be held up voluntarily

Or diseases which have dystonia as a feature (ie Schiff sherington posture) but have other neurolocalising signs to determine the underlying pathology.

Note, however that in most cases a structural cause is not found and it is thought most cases represent a functional disorder of the basal nuclei/movement pathways

Question 26

Medical treatments reported for paroxysmal dyskinesias in JVIM 2022 review summary

Answer 26

Various Tx and variable results - not surprising when likely dealing with >1 pathology

AEDs - phenobarbital PxD areported as have levetiracetam responsive

Clonazepam reported to be effective in many cases of CKCS episodic falling syndrome

Not enough evidence to make clear recommendations - look into specific recommendations for specific breed-associated diseases and use empirical evidence

Spontaneous remissions are also reported complicating investigation into effective treatments

If episodes are infrequent treatment may not be necessary, or can practice avoidance of particular stimulus.

Efficacy of medications is proposed to be through exertion of effect through monoamine neurotransmitter receptors

Gluten free diet trials are recommended in Border Terriers and Maltese based on recent case series.

Question 27

How to describe Dystonia

Answer 27

Activity being performed at onset (e.g., resting, running, or exercise-induced)
Body distribution (focal, segmental, generalised)
Duration
Responsiveness
Severity,
Temporal pattern (i.e., paroxysmal or persistent, severity at onset and at later stages)
The presence or lack of autonomic signs (e.g., salivation)
The presence or lack of preceding signs (e.g., restlessness)
The presence or lack of signs after resolution of dystonia (e.g., sleepiness)
Coexistence of other movement disorders, and other neurologic manifestations