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)

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