UMN Lesions

Upper Motor Neuron (UMN) Lesions vs Lower Motor Neuron (LMN) Lesions UMN Lesions:

• Location: Cerebral hemisphere, cerebellum, brain stem, spinal cord Inspection:
  • No fasciculations
    o No significant wasting
  • Mild atrophy with contractures may be present
• Tone:
  • Increased (spasticity or rigidity)
    o Ankle clonus present
• Reflexes:
  • Exaggerated or brisk (hyperlexia)
    o Positive Babinski sign
• Power:
  • Reduced strength with a pyramidal pattern of weakness
    o Arms: Extensors weaker than flexors
    o Legs: Extensors are stronger than flexors
• Associated conditions:
  • Ischaemic/haemorrhagic stroke
  • ALS
    o MS

LMN Lesions:

• Location: Anterior horn cells, motor nerve roots, peripheral motor nerves Inspection:
  • Muscle wasting
    o Fasciculations present
• Tone:
  o Decreased (hypotonia, flaccid) or normal Power:
  • Reduced along the motor root/nerve Reflexes:
  • Decreased or absent
    o plantar reflexes – normal or no movement
• Associated conditions:
  o Peripheral nerve trauma/compression
  o Guillain-Barré syndrome
  o ALS
  • Polymyositis

UMN VS. LMN Reference