Motor neurone disease

Question 1

MND : Anatomy of Corticospinal tract

Answer 1

MOA : Responsible for controlling voluntary movements in the limbs.

Corticospinal tract
1. Origin : Motor cortex
* UMN form part of the corticospinal tract and extend axons into;
2. Mid brain
3. Medulla : UMN crossover
4. Spinal Chord - Anterior horn
UMN synapse with LMN
5. Neuromuscular junction
LMN synapses with muscle

6. Movement occurs

Question 2

MND : Anatomy of Corticobulbar tract

Answer 2

MOA :
* Neural pathway responsible for providing motor innervation to the cranial nerve nuclei in the brainstem,

• which, in turn, control the muscles of the face, head, and neck

Origin : Primary Motor cortex
* Upper motor neurons form part of the corticobulbar tract and extend axons to;

1 . Internal capsule :
* Bundle of nerve fibres - pathway connected cerebral cortex and brainstem

2 .Pons : UMNs cross over

. 3 .Brain stem nuclei : UMN synapse with LMN
* Contains cranial nerve nuclei : facial nerve nucleus, trigeminal nerve nucleus, hypoglossal nucleus } control voluntary movement of head and neck.

Question 3

Corticobulbar palsy : Clinical features

Answer 3

The degeneration of upper motor neurons in the corticobulbar tract effects the motor commands that influence the function of cranial nerves in the brainstem.

1. Dysarthria and Dysphagia
* Degeneration of the hypoglossal nucleus and nerve leads to tongue weakness and atrophy

2. Dysphagia and Hoarse/Weak voice
* Degeneration of Glossopharyngeal (IX), vagus (X), and accessory (XI) nerves.

3. Facial weakness, loss of expression
* facial nerve nucleus degeneration leads to facial weakness and a loss of voluntary facial movements

Question 4

Motor neurone disease : Definition

Answer 4

Motor neurone disease involves a progressive degeneration of both the upper and lower motor neurones.

The sensory neuronesare spared.

Question 5

Motor neurone disease : Incidence

Answer 5

Late - middle aged men (around 60 years old)

Question 6

Motor neurone disease : Clinical presentation

Answer 6

Onset : Slow, progressive weakness of muscles
1. Limb weakness : worse on exercise
2. Increased, clumsiness and falls
3. Lower motor neuron signs > Upper motor neuron signs
* Both occur

Question 7

Motor neurone disease : UMN signs/Sx

Answer 7

1 . Hyperreflexia:
* a loss of inhibitory input on the reflex arc.
* This disinhibition results in exaggerated reflex responses, known as hyperreflexia
.

*Clinical Sign: Increased deep tendon reflexes, such as brisk knee jerk reflexes.

2 . Hypertonia/Spasticity
* Disrupts the balance between excitatory and inhibitory signals to lower motor neurons,
* leading to increased muscle tone and spasticity.

Clinical Sign: Resistance to passive movement, with muscles feeling stiff and tense.

3 . Weakness:
* impairs the descending signals that normally facilitate voluntary muscle contraction..

Clinical Sign: Weakness, typically more pronounced in the extensor muscles.

4 . Babinski Sign:**

• normal: the plantar reflex is flexor in response to stimulation.
• Abnormal : extensor (upward) response in the toes and suggests UMN involvement.

Clinical Sign: Babinski sign involves dorsiflexion of the big toe and fanning of the other toes.

Question 8

Motor neurone disease : LMN signs/Sx

Answer 8

Damage to Lower Motor Neurone causes;

!) Hyporeflexia/Areflexia:
* decreased or absent reflex responses.
* Clinical Sign: Diminished or absent deep tendon reflexes.

2) Hypotonia/Flaccidity:
leads to a lack of muscle tone and atrophy due to denervation.
* Clinical Sign:* Muscles feel floppy, and there is a noticeable loss of bulk.

3) Fasciculations
Spontaneous contractions of a bundle of muscle fibers.
Instability of the motor endplate due to denervation.

• Clinical Sign : Visible twitching or rippling of muscles, often seen under the skin.

4) Muscle Atrophy:
Denervation of muscles leads to disuse atrophy, resulting in a reduction in muscle bulk.
* Clinical Sign:* Noticeable wasting of muscles.

5) Absent Babinski Sign
the Babinski sign is typically absent, as it is a reflection of an upper motor neuron response.
* Clinical Sign: The normal plantar reflex response is observed.

Question 9

ALS - Definition

Answer 9

1. This is a degenerative motor neurone disorder
2. Involved both Upper and lower motor neuron lesions
3. Lower motor neurone signs

Question 10

ALS - Aetiology

Answer 10

Genetic mutation : Superoxide Dismutase 1
**MOA **:
* enzyme important for removing free oxygen radicals from neurons
,without this;
* increased free radical injury, which will lead to neuron death.

Question 11

ALS : Pathophysiology

Answer 11

1. Neuronal damage in ;
   * Anterior Horn of Spinal Chord : Lower motor neurone affected
   * Cortical (Cerebral cortex) : Upper motor neurones affected in the
2. Coritospinal pathway
3. Corticobulbar spinal pathways of cranial nerves

Symptoms dependant on which spinal tract is affected

Question 12

ALS : Clinical features

Answer 12

1. Mixed Upper and Lower motor neuron signs
2. Asymmetric limb weakness
3. Wasting of small hand muscles
4. Faciculations
5. Corticobulbar pathway damage :
   * Head, Neck weakness
   * Dysarthria, Dysphagia

No
* No Sensory symptoms - Bladder and Bowel function spared
* No impact on external ocular muscles
* No Cognitive damage
* No Cerebellar damage

Question 13

ALS : Diagnosis

Answer 13

1. Nerve conduction - r/o neuropathy
2. MRI - r/o chord compression

Question 14

ALS : Management

Answer 14

1. Riluzole
   Prevents glutamate receptor stimulation
   Prolongs life by around 3 months
2. NIV - for respiratory care
3. Nutrition
   * percutaneous gastrostomy tube (PEG) is the preferred way to support nutrition and has been associated with prolonged survival

Question 15

Motor neurone disease : Prognosis

Answer 15

• Eventually, the disease might progress to involve the breathing muscles and can lead to respiratory failure and death.
• poor: 50% of patients die within 3 years

Question 16

Progressive bulbar palsy : Definition

Answer 16

1. Progressive Bulbar Palsy (PBP) is a type of Amyotrophic Lateral Sclerosis (ALS),
2. a progressive neurodegenerative disorder that affects the motor neurons in the brain and spinal cord.
3. PBP specifically involves the bulbar region, which includes
   * the brainstem and the cranial nerves responsible for functions such as speech, swallowing, and facial movements.

Question 17

Progressive bulbar palsy : Clinical features

Answer 17

Prominently bulbar symptoms - some associated limb weakness from effects on spinothalamic tract
1. Dysarthria : earliest, most prominent symptoms
2. Dysphagia / Tongue atrophy
3. Facial weakness

4. Normal Sensation and cognition

Question 18

Pseudobulbar palsy : Definition

Answer 18

• Neurological condition characterized by the dysfunction of the upper motor neurons that innervate the bulbar muscles.
• “pseudobulbar” - Cranial nuclei and Lower motor neurons are intact
• Primary pathology lies in the upper motor neurons
  symptoms mimic those seen in bulbar palsy

Question 19

Pseudobulbar palsy : Causes

Answer 19

various neurological conditions that affect the upper motor neurons, such as

1. Stroke,
2. traumatic brain injury
3. multiple sclerosis
4. neurodegenerative disorders.

Question 20

Pseudobulbar palsy : Clinical features

Answer 20

1. Bulbar Symptoms:
   * dysarthria (difficulty in articulating words), dysphagia (difficulty swallowing), and facial weakness.

2). Upper Motor Neuron Involvement:
* Increased muscle tone and spasticity } common
* overactivity of the upper motor neurons
* stiff and jerky movements.

Question 21

Subacute combined degeneration of the spinal cord : Definition

Answer 21

• Subacute combined degeneration of the spinal cord
• Due to vitamin B12 deficiency resulting in;
• impairment of the dorsal columns, lateral corticospinal tracts and spinocerebellar tracts

Question 22

SCD of Spinal Chord : Pathophysiology

Answer 22

Cause
1. Vitamin B12 / Cobalamin deficiency.

• Vitamin B12 required for
  synthesis of myelin
• DNA repair and maintainance in neuronal cells

2. Lack of vitamin B12 leads to;

• Demyelination and degeneration of nerve fibers in the spinal cord.

3. Particularly affecting the dorsal (posterior) and lateral columns.

Recreational nitrous oxide inhalation may also result in vitamin B12 deficiency → subacute combined degeneration of the spinal cord.

Question 23

SCD of Spinal Chord : Risk factors

Answer 23

Risk factors - same as for vitamin B12 deficiency

1. Inadequate dietary intake
2. Malabsorption disorders
3. Medications (e.g., proton pump inhibitors, metformin).

Question 24

SCD of Spinal Chord : Clinical features

Answer 24

Symmetrical involvement - Symptoms present bilaterally

1. Dorsal column affected :

MOA : responsible for transmitting proprioceptive (position sense) and vibratory sensation - resulting in

• Sensory Ataxia: unsteady, clumsy gait
  
  • Loss of Vibratory Sensation: numbness, tingling, and loss of vibratory sensation, particularly in the lower extremities.
  • Paresthesias: “pins and needles” may occur.

2. Lateral Corticospinal Columns:
   MOA : responsible for voluntary motor function
   Degeneration of this leads to;

• Upper motor neuron signs
• Spasticity and weakness.
• Weakness and Muscle Atrophy
• Difficulty with Fine Motor Skills

3. Macrocytic Anemia: pernicious anemia, contributing to fatigue and weakness.

Question 25

SCD of Spinal Chord : Prognosis

Answer 25

1. Prompt managaement - allows for reversal of symptoms
2. Untreated - progresses to permanent neurological deficits.