Motor neuron disease Flashcards
What is weakness or paresis
Impaired ability to move a body part in response to will
Paralysis
Ability to move a body part in response to will is completely lost
Ataxia
Incoordination
Willed movements are clumsy, ill-directional or uncontrolled
Involuntary movement
Spontaneous movement of a body part, independently of will
Apraxia
Disorder of consciously organised pattern of movement or impaired ability to recall acquired motor skills e.g. brushing teeth or striking a match
*Describe the organisation of movement by body
- Idea of the movement - association areas of cortex
- Activation of upper motor neurones in the pre-central gyrus
- Impulses travel to lower motor neurones and their motor units (A-alpha motor neurone and all the skeletal fibres it innervates) via the coricospical tract
- Modulating activity of the cerebellum and basal ganglia
- Further modification of movement depending on sensory feedback
Where are Lower Motor neurones located
Anterior horns of the spinal cord and in cranial nerve nuclei in brainstem
What is a motor unit
Alpha motor neurone (LMN) and all (skeletal) muscle fibres it innervates
What is motor neurone pool
Collection of motor neurones innervating a single skeletal muscle
What is a motor end plate
Region of the cell membrane of the muscle fibre which lies directly beneath an axon terminal
How is muscle tone regulated
Stretch receptors in muscle (MUSCLE SPINDLES) innervated by GAMMA MOTOR NEURONES
Muscle stretched → afferent impulses FROM muscle spindles → reflex partial contraction of muscle
How is muscle tone affected by disease
Disease states e.g. spasticity and rigidity ALTER MUSCLE TONE by altering the sensitivity of this reflex
Potential sites of damage along motor pathway
- Motor nuclei of cranial nerves
- Motor neurones in spinal cord
- Spinal ventral roots
- Peripheral nerves
- Neuromuscular junction
- Muscle
Upper motor neurone lesion signs
Spasticity (increased muscle tone)
Brisk reflexes - tendon and jaw reflexes
Plantars are upturned on stimulation (positive Babinski sign)
Limb muscle weakness (pyramidal pattern)
Describe the pattern of limb muscle weakness in an UMN lesion
Upper limbs extensor muscles are weaker than flexors
Lower limbs flexor muscles are weaker then extensors
Finer more skilful movement are impaired
Lower motor neurone lesion signs
Muscle tone reduced - FLACCID
Muscle wasting
Reflexes depressed or absent
Fasciculation (of tongue)
What is fasciculation
Visible spontaneous contraction of motor units
not enough by itself to diagnose LMN lesion
What is motor neurone disease
Cluster of major degenerative diseases characterised by selective loss of neurones in motor cortex, cranial nerve nuclei and anterior horn cells
Epidemiology of MND
Uncommon
More in males
Median age of onset = 60
Often fatal in 2-4 years
Aetiology of MND
Usually sporadic and of unknown cause
One familial variant involves mutations in free radical scavenging enzyme copper/zinc superoxide dismutase (SOD-1)
Pathophysiology of MND
Motor neurones destroyed, namely anterior horn cells of the spinal cord and motor cranial nuclei -> LMN and UMN dysfunction -> Mixed picture of muscular paralysis
Caused reactive oxygen species which damage DNA, lipids & proteins
What distinguishes MND from MS and polyneuropathies
Upper and lower MNs affected in MND
No sensory loss or sphincter disturbance in MND (unlike in MS and polyneuropathies)
What distinguishes MND from myasthenia gravis
MND never affects Eye Movements
What causes patients to die in MND generally
Most patients die within 3 years from respiratory failure as a result of bulbar
palsy (impairment of CN 9,10,11,12) and pneumonia
Types of MND
Amyotrophic Lateral Sclerosis (ALP)
Progressive Muscular Atrophy (PMA)
Progressive Bulbar Palsy (PBP)
Primary Lateral Sclerosis (PLS)
Most common MND
Amyotrophic Lateral Sclerosis
Least common MND
Primary Lateral Sclerosis
What is Amyotrophic lateral sclerosis
Affects UMN and LMN
Loss of motor neurones in motor cortex and anterior horn of the cord
Weakness + UMN signs + LMN wasting/fasciculations - usually in one limb
Signs of amyotrophic lateral sclerosis
Weakness + UMN signs + LMN wasting/fasciculations - usually in one limb
Split hand sign
Cramps are a common but non-specific symptom
Wrist and foot drop
Examination reveals UMN signs such as brisk reflexes (in a wasted muscle), extensor plantar response and spasticity
What is progressive muscular atrophy
LMN only
Presentation with weakness, muscle wasting and fasciculations usually starting in one limb and gradually spreading to involve other adjacent spinal segments
Affects distal muscles before proximal
What is primary lateral sclerosis
UMN only
Loss of Betz cells in motor cortex
Mainly UMN signs + marked spastic leg wekness with progressive tetraparesis and pseudobulbar palsy
No cognitive decline
What is progressive bulbar palsy
UMN and LMN of lower cranial nerves
Lower cranial nerves (9, 10, 11, 12) and nuclei initially only affected
Signs and symptoms of progressive bulbar palsy
Dysarthria, Dysphagia, Nasal regurgitation of fluids, Choking are presenting symptoms
LMN lesion of tongue and muscles of talking and swallowing - flaccid, fasciculating tongue (like a sack of worms), jaw jerk is normal/absent, speech is quiet, hoarse or nasal
Which MND affects UMNs
Primary lateral sclerosis (only UMN)
Amyotrophic lateral sclerosis (affects UMN and LMNs)
(Progressive bulbar palsy - affects UMN and LMN of cranial nerves lower down 9-12)
Which MND affects LMNs
Progressive muscular atrophy (only LMN)
Amyotrophic lateral sclerosis (affects UMN and LMNs)
(Progressive bulbar palsy - affects UMN and LMN of cranial nerves lower down 9-12)
Which MNDs affect UMN and LMN
Amyotrophic lateral sclerosis (affects UMN and LMNs)
Progressive bulbar palsy - affects UMN and LMN of cranial nerves lower down 9-12
General clinical presentation of MND
Upper limbs, Lower limbs, Bulbar, Overall
Varies with type.
Generally:
Upper limbs: reduced dexterity, stiffness, wasting of intrinsic muscles of the hand
Lower limbs: tripping, stumbling gait, foot drop
Bulbar (Progressive Bulbar Palsy): Slurred speech, hoarseness, dysphagia
Overall: Muscle atrophy and spasticity
Differential diagnosis of MND
MS or polyneuropathies but no sensory loss or sphincter disturbance (in MND)
Myasthenia gravis, but does not affect eye movements in MND
Diabetic amyotrophy
Guillain-Barre syndrome
Spinal cord syndrome
Diagnosis
Clinical (fasciculation)
Electromyography (EMG) - confirms muscle denervation due to LMN degeneration
Also:
Nerve conduction studies
Brain/cord MRI
Lumbar puncture
Based on clinical findings - how likely depends on number of signs
In diagnosis of MND, what is purpose of:
Brain/cord MRI
Lumbar puncture
Brain/cord MRI helps to exclude structural causes
Lumbar puncture to exclude inflammatory causes
Diagnosis of MND based on clinical findings
Definite: LMN + UMN signs in 3 regions
Probable: LMN + UMN signs in 2 regions
Probably with lab support: LMN + UMN signs in 1 region or UMN sign in more than 1 region and EMG (electromyography) shows acute denervation in >2 limbs
Possible: LMN + UMN signs in 1 region
Suspected: LMN OR UMN sign only in at least 1 region
Complications of MND
Most die in 3 years from respiratory failure due to bulbar palsy and pneumonia
Treatment of MND
Sodium channel blocker: Riluzole, inhibits glutamate release (Antiglutamatergic drug) and is a NMDA receptor antagonist
Symptomatic: Baclofen (for spasms)
Analgesia e.g. NSAIDs (Diclofenac) or opioids
Extra treatment for Bulbar palsy
Wasting of muscles of mastication
Amitriptyline (oral)
Age of onset
> 40 years
Median age of onset is 60
What is the diagnostic criteria for ALS called
El Escorial diagnostic criteria
Describe the El Escorial diagnostic criteria for ALS
Definite = UMN and LMN signs in 3 regions
Probable = UMN and LMN signs in 2 regions
Probable with lab support = UMN and LMN signs in 1 region OR UMN signs in at least 1 region and EMG shows acute denervation
Possible = UMN and LMN signs in 1 region
Suspected = UMN or LMN signs in at least 1 region
