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Medicine Phase 2a Neuro > Motor neuron disease > Flashcards

Motor neuron disease Flashcards

1
Q

What is weakness or paresis

A

Impaired ability to move a body part in response to will

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2
Q

Paralysis

A

Ability to move a body part in response to will is completely lost

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3
Q

Ataxia

A

Incoordination

Willed movements are clumsy, ill-directional or uncontrolled

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4
Q

Involuntary movement

A

Spontaneous movement of a body part, independently of will

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5
Q

Apraxia

A

Disorder of consciously organised pattern of movement or impaired ability to recall acquired motor skills e.g. brushing teeth or striking a match

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6
Q

*Describe the organisation of movement by body

A
  1. Idea of the movement - association areas of cortex
  2. Activation of upper motor neurones in the pre-central gyrus
  3. 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
  4. Modulating activity of the cerebellum and basal ganglia
  5. Further modification of movement depending on sensory feedback
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7
Q

Where are Lower Motor neurones located

A

Anterior horns of the spinal cord and in cranial nerve nuclei in brainstem

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8
Q

What is a motor unit

A

Alpha motor neurone (LMN) and all (skeletal) muscle fibres it innervates

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9
Q

What is motor neurone pool

A

Collection of motor neurones innervating a single skeletal muscle

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10
Q

What is a motor end plate

A

Region of the cell membrane of the muscle fibre which lies directly beneath an axon terminal

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11
Q

How is muscle tone regulated

A

Stretch receptors in muscle (MUSCLE SPINDLES) innervated by GAMMA MOTOR NEURONES
Muscle stretched → afferent impulses FROM muscle spindles → reflex partial contraction of muscle

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12
Q

How is muscle tone affected by disease

A

Disease states e.g. spasticity and rigidity ALTER MUSCLE TONE by altering the sensitivity of this reflex

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13
Q

Potential sites of damage along motor pathway

A
  • Motor nuclei of cranial nerves
  • Motor neurones in spinal cord
  • Spinal ventral roots
  • Peripheral nerves
  • Neuromuscular junction
  • Muscle
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14
Q

Upper motor neurone lesion signs

A

Spasticity (increased muscle tone)
Brisk reflexes - tendon and jaw reflexes
Plantars are upturned on stimulation (positive Babinski sign)
Limb muscle weakness (pyramidal pattern)

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15
Q

Describe the pattern of limb muscle weakness in an UMN lesion

A

Upper limbs extensor muscles are weaker than flexors
Lower limbs flexor muscles are weaker then extensors
Finer more skilful movement are impaired

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16
Q

Lower motor neurone lesion signs

A

Muscle tone reduced - FLACCID
Muscle wasting
Reflexes depressed or absent
Fasciculation (of tongue)

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17
Q

What is fasciculation

A

Visible spontaneous contraction of motor units

not enough by itself to diagnose LMN lesion

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18
Q

What is motor neurone disease

A

Cluster of major degenerative diseases characterised by selective loss of neurones in motor cortex, cranial nerve nuclei and anterior horn cells

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19
Q

Epidemiology of MND

A

Uncommon
More in males
Median age of onset = 60
Often fatal in 2-4 years

20
Q

Aetiology of MND

A

Usually sporadic and of unknown cause

One familial variant involves mutations in free radical scavenging enzyme copper/zinc superoxide dismutase (SOD-1)

21
Q

Pathophysiology of MND

A

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

22
Q

What distinguishes MND from MS and polyneuropathies

A

Upper and lower MNs affected in MND

No sensory loss or sphincter disturbance in MND (unlike in MS and polyneuropathies)

23
Q

What distinguishes MND from myasthenia gravis

A

MND never affects Eye Movements

24
Q

What causes patients to die in MND generally

A

Most patients die within 3 years from respiratory failure as a result of bulbar
palsy (impairment of CN 9,10,11,12) and pneumonia

25
Q

Types of MND

A

Amyotrophic Lateral Sclerosis (ALP)
Progressive Muscular Atrophy (PMA)
Progressive Bulbar Palsy (PBP)
Primary Lateral Sclerosis (PLS)

26
Q

Most common MND

A

Amyotrophic Lateral Sclerosis

27
Q

Least common MND

A

Primary Lateral Sclerosis

28
Q

What is Amyotrophic lateral sclerosis

A

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

29
Q

Signs of amyotrophic lateral sclerosis

A

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

30
Q

What is progressive muscular atrophy

A

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

31
Q

What is primary lateral sclerosis

A

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

32
Q

What is progressive bulbar palsy

A

UMN and LMN of lower cranial nerves

Lower cranial nerves (9, 10, 11, 12) and nuclei initially only affected

33
Q

Signs and symptoms of progressive bulbar palsy

A

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

34
Q

Which MND affects UMNs

A

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)

35
Q

Which MND affects LMNs

A

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)

36
Q

Which MNDs affect UMN and LMN

A

Amyotrophic lateral sclerosis (affects UMN and LMNs)

Progressive bulbar palsy - affects UMN and LMN of cranial nerves lower down 9-12

37
Q

General clinical presentation of MND

Upper limbs, Lower limbs, Bulbar, Overall

A

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

38
Q

Differential diagnosis of MND

A

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

39
Q

Diagnosis

A

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

40
Q

In diagnosis of MND, what is purpose of:
Brain/cord MRI
Lumbar puncture

A

Brain/cord MRI helps to exclude structural causes

Lumbar puncture to exclude inflammatory causes

41
Q

Diagnosis of MND based on clinical findings

A

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

42
Q

Complications of MND

A

Most die in 3 years from respiratory failure due to bulbar palsy and pneumonia

43
Q

Treatment of MND

A

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

44
Q

Extra treatment for Bulbar palsy

A

Wasting of muscles of mastication

Amitriptyline (oral)

45
Q

Age of onset

A

> 40 years

Median age of onset is 60

46
Q

What is the diagnostic criteria for ALS called

A

El Escorial diagnostic criteria

47
Q

Describe the El Escorial diagnostic criteria for ALS

A

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

Medicine Phase 2a Neuro (28 decks)

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