Movement disorders Flashcards
Define Dystonia
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
Types of peripheral nerve hyperexcitability (7)
Paroxysmal Dyskinesias
Myokymia
Fasciculations
Cramps
Myotonia
Neuromyotonia
Tetany
Importance of basal nuclei/ganglia
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)
Importance of caudate- putatem
Overriding modulatory control of the basal nuclei
–> D1 R activation increases glutaminergic activity
–> D2 R activity decreases glutaminergic activity
Components of basal ganglia
Caudate nucleus
Putamen
(together those are striatum)
Globus pallidus (internal and external)
Subthalamic nucleus
Substantia nigra
Steps of DIRECT movement pathway and main function
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
Steps of INDIRECT Movement pathway and its main function
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.
Dopamine role in movement pathways
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
What is chorea
abrupt (jerky), non-patterned and un-sustained low amplitude contraction of muscle groups
What is dyskinesia
Dyskinesia = self limiting, episodic, involuntary movements that are recurrent
What is athetosis
Prolonged slow involuntary contraction of the trunk muscles –> nonrhythmic bending and writhing movements
–> prevents stable maintenance of posture
What is ballism
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.
What is myokymia
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
What is myoclonus
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
What is myotonia and neuromyotonia
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
What are fasciculations
Brief spontaneous contraction of a small muscle group, no limb or body movement
What is tetany
Sustained muscle contraction usually involving extensor muscles
What are tremors and what types are there
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
General approach to movement disorders JVIM 2022 ECVN consensus
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)
Difference b/w hyper and hypokinetic disorders
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
Possible causes of acquired paroxysmal dyskinesias
Propofol - dystonia
Phenobarbital - dyskinesia
Structural intracranial lesions
Paroxysmal gluten sensitive dyskinesia of Border Terriers
Tetanus toxicity
Paroxysmal dyskinesias in dogs that have genetic test and other breeds affected
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
Peripheral nerve hyperexcitability disorders cause and symptoms
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
Definition of and types of Tremor
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
