Upper and Lower Motor Neuron Lesions

• Reflexes
• Tone
• Power
• Fasciculation
• Muscle bulk

Inspection

• Muscle bulk: loss of muscle bulk in LMN and late in UMN
• Symmetry
• Fasciculation: present in LMN, none in UMN

Muscle Tone

• Flexion/extension, pronation/supination of joint through its ROM
  • Hypotonia (flaccidity) – LMN lesions, spinal shock, cerebellar lesions
  • Hypertonia
    • Spasticity – UMN lesion
      • Limb moves, then catches, and then goes past catch (clasp-knife)
      • Test by rapidly supinating forearm
    • Rigidity – LMN lesions, extrapyrimidal tract lesion
      • Increased tone throughout ROM (cog-wheeling, lead-pipe)
      • Circumducting the wrist

 

Power (compare between L and R)

• UMN → flexors > extensors in upper limbs, extensors > flexors in lower limbs
• LMN → reduced power in specific motor neuron distribution
  • deltoids – arm abduction – C5 C6 (axillary)
  • biceps – elbow flexion – C5 C6 (musculocutaneous)
  • triceps – elbow extension – C6 C7 C8 (radial)
  • thumb flexion – C6 C7 (median)
  • wrist extensors – C7 C8 (radial)
  • interossei of hand – finger abduction/adduction – C8 T1 (ulnar)
  • hip flexion – L1 L2 L3 (femoral)
  • hip adduction – L2 L3 L4 (obturator)
  • hip abduction – L4 L5 S1 (superior gluteal)
  • knee extension – L2 L3 L4 (femoral)
  • knee flexion – L5 S1 S2 (sciatic)
  • ankle dorsiflexion – L4 L5 (deep peroneal)
  • ankle plantar flexion – S1 S2 (tibial)
  • foot inversion – L4 L5 (posterior tibial)
  • foot eversion – L5 S1 (superficial peroneal)

* GRADE

                  0                nil

                  1                flicker of movement

                  2                movement cannot overcome gravity

                  3                movement cannot overcome any resistance

                  4                movement is weaker than normal

                  5                normal

Special tests

• Pronator drift
  • Stand with eyes closed and arms held straight out and hands supinated         
    • + → Patient cannot maintain this position
    • Muscle weakness (pronation and outward drift)
    • UMN lesion (pronation and downward drift)
• Fine finger movements
  • Touch each finger to crease of thumb (show patient how) and speed it up
  • Look for right and left differences, slow if UMN lesion

 Reflex

• Deep tendon reflex (DTR)
  • Biceps tendon (C5-6)
  • Brachioradialis tendon (C5-6)
  • Triceps tendon (C6-8)
  • Knee jerk (L2-4)
  • Achilles tendon (S1-2)
• Hyperactive ankle jerk → examine for clonus at knee and ankle
• Absent → use reinforcements (teeth clenching for UL, Jendrassik’s maneuver for LL)
• UMN → Hyperreflexia, but may be flaccid
• LMN → Diminished reflexes

Grade*                     0          nil

                                    1          low normal

                                    2          normal

                                    3          high normal

                                    4          clonus (sustained > 3 beats)

 * Note if reinforcements used (teeth clenching, hand grips)

• Babinski’s reflex (L5-S1)
  • + → Dorsiflexion of the big toe with fanning of the other toes (UMN lesion)