Clinical Lecture: LMN/UMN Disorders

Question 1

Give causes of muscle weakness.

Answer 1

1. Upper Motor Neurone Pathologies e.g. Stroke, Tumour etc.
2. Lower motor neurone e.g. motor neurone disease, root damage, periphery neuropathy, single nerve damage).
3. Neuromuscular Junction e.g. Myasthenia Gravis
4. Myopathy
5. Non-specific e.g. systemic illness
6. Function e.g. poor effort, hysteria, malingering.

Question 2

Compare the presentation of UMN Disorders from that of LMN Disorders.

Answer 2

UMN

• Positive Plantar reflex
• Increased Tone
• Brisk Reflex
• Mild Atropy
• Weakness

LMN

• Downgoing Plantars
• Depressed or absent Reflex
• Decreased Tone
• Weakness
• Mild atrophy

Question 3

Give common Lower Motor Pathologies.

Answer 3

• Muscular pathologies e.g. Myopathy
• Neuromuscular Junction disease e.g. Myasthenia Gravis
• Nerve Pathologies - Focal such as Carpal tunnel syndrome or Gneralised such as in Polyneuropathy due to diabetes
• Root Pathology e.g. radiculopathy
• Anterior Horn disease e.g. poliomyelitis

Question 4

What is Motor Neurone Disease?

Answer 4

• Disease of motor neurons (UMN & LMN) - more common to get both involve
  
  • Progressive motor deficit with an unknown (idiopathic) cause
  • Sporadic cause with 5-10% of cases genetic cause (familial basis)
  • There is suggestion that it is related to toxins, viruses, trauma, or combinations

Clinical features

- Progressive motor weakness that can affect tongue, face and speech muscles 
- No sensory symptoms 
- Painless 
- Poor prognosis - mean survival is usually 3-5 years 
- Dysphagia, dysarthria, nasal regurgitation and aspiration

Question 5

What can we use to investigate UMN/LMN lesions?

Answer 5

• Nerve Conduction Studies
• Needle Electromyography - here we look for spontaneous activity, motor unit potential analysis and pattern of recruitment.