Motor Neuron Disease

Question 1

What is motor neuron disease?

Answer 1

Motor neuron diseases are a group of progressive neurological disorders that destroy cortical, brainstem and spinal motor neurons, the cells that control voluntary muscle activity such as speaking, walking, breathing, and swallowing.
● No sensory loss

Question 2

What are the different subtypes of MND?

Answer 2

1. Amyotrophic Lateral Sclerosis (ALS)
   ● AKA Lou Gehrig’s disease
   ● Combined degeneration of upper AND lower motor neurones resulting in a mix of LMN and UMN signs
2. Progressive Muscular Atrophy Variant
   ● Only LMN signs
   ● Better prognosis
3. Progressive Bulbar Palsy Variant
   ● Only affects CN IX-XII (9-12)
   ● Dysarthria (difficulty speaking)
   ● Dysphagia (difficulty swallowing)
   ● Wasted fasciculating tongue
   ● Brisk jaw jerk reflex
4. Primary Lateral Sclerosis Variant
   ● Loss of Betz cells in motor cortex
   ● UMN pattern of weakness
   ● Brisk reflexes
   ● Extensor plantar responses
   ● NO LMN signs

Question 3

Describe the aetiology of MND

Answer 3

• MND is associated with misfolding of the TDP-43 protein in many cases.
• It can be an inherited condition, with several associated genes yet to be identified.
• About 2% of total cases are associated with a mutation in the SOD-1 gene.

Question 4

Summarise the epidemiology of motor neurone disease

Answer 4

● RARE
● Incidence: 6/100,000
● Mean age of onset: 55 yrs
● 5-10% have a family history with autosomal dominant inheritance

Question 5

What are the presenting symptoms of MND?

Answer 5

● Weakness of limbs – proximal myopathy
● Speech disturbance (slurring or reduction in volume)
● Swallowing disturbance (e.g. choking on food)
● Behavioural changes (e.g. disinhibition, emotional lability)
Asymmetrical Symptoms (unlike other neurological conditions)

Question 6

What signs of MND can be found on physical examination?

Answer 6

Combination of UMN and LMN signs
- progressive muscle weakness
- shortness of breath
- wasting of thenar muscles and wasting of tongue base
1. LMN Features:
o Muscle wasting
o Fasciculations i.e. of tongue, abdomen, back and thigh
o Flaccid weakness
o Hyporeflexia
- hypotonia
- fibrillations
2. UMN Features:
o Spastic weakness
o Extensor plantar response
o Hyperreflexia
- clonus
- babinski sign
3. Sensory examination - should be NORMAL
4. Frontotemporal dementia occurs in 25%
5. Eye movements normal

Question 7

What investigations are used to diagnose/ monitor MND?

Answer 7

1. Bloods
   o Mild elevation in CK
   o ESR
   o Anti-GM1 ganglioside antibodies
2. Electromyography (EMG)- show signs of denervation
3. Nerve conduction studies - often normal
4. MRI - exclude cord compression and brainstem lesions
5. Spirometry - assess respiratory muscle weakness
6. Lumbar Puncture can help exclude inflammatory causes

Question 8

How is MND managed?

Answer 8

• Riluzole → 1st line. Glutamate antagonist. Prolongs life by around 3 months.
• Respiratory Care → usually BIPAP (NIV) at night (for type 2 respiratory failure)

Question 9

What complications may arise from MND?

Answer 9

Respiratory failure, nutritional deficit, aspiration pneumonia, fronto-temporal dementia