Laryngeal Electromyography (LEMG):

• Evaluates integrity of laryngeal neuromuscular system in by recording action potentials generated in laryngeal muscles during voluntary and involuntary contraction.
• Most effective between 1-6 months post onset of paralysis.

Tests 3 laryngeal muscles:

1. ThyroArtyenoid (TA):
   • Evaluation  of RLN .
   • Needle placement is confirmed by vocalisation .
2. Postereior CricoArytenoid (PCA):
   • Evaluation  of RLN.
   • Needle placement is confirmed by sniffing.
3. CricoThyroid (CT):
   • Evaluation  of SLN.
   • Needle placement is confirmed by glide from one pitch to another.

Indications of LEMG:

Interpretation of Laryngeal Electromyography :

1. Normal LEMG:
   • Bi or Triphasic Motor-Unit Potentials.
   • Seen in patients with CricoArytenoid Fixation.
2. Neuropathy:
   • Fibrillation Potentials:
     • Abnormal spontaneous activity at rest.
     • Due to ongoing axonal degenerat ion .
     • Starts after 3 weeks of injury.
     • Persist until Re-innervation occurs or until the motor endplates of the muscle degenerate (Myopathic injury ) .
   • Sharp waves:
     • Lower Frequency
     • Normal Amplitude
3. Muscle Re-innervation after Neuropathic injury:
   • Polyp hasic Potentials
     • > 4 phases.
     • Due to Not well synchronized muscle fibers.
4. Myopathy:
   • Decreased functioning muscle fibers.
     • Polyphasic .
     • Low Amplitude .
     • Low Duration

Laryngeal Electromyography Graphs and Findings

Laryngeal Muscles:

Extrinsic Muscles:

• Attach Larynx to adjacent structures.
  • Elevators:
    • Primary Elevators:
      • Act directy as they are attached to Thyroid cartilage:
        • 1. ThyroHyoid (C1)
        • 2. StyloPharyngeus (CN-IX)
        • 3. PalatoPharyngeus (CN-X)
        • 4. SalpingPharyngeus (CN-X)
    • Secondary Elevators:
      • Act directly as they are attached to Hyoid bone:
        • 1. GenioHyoid (C1)
        • 2. Mylohyoid (CN-V3)
        • 3. Digastric:
          • Ant. belly (CN-V3)
          • Post. belly (CN_VII)
        • 4. StyloHyoid (CN-VII)
  • Depressors:
    • Infra-Hyoid Muscles (Strap):
      • 1. ThyroHyoid (C1)
      • 2. OrnoHyoid (C1-C3)
      • 3. SternoTyroid (C1-C3)
      • 4. SternoHyoid (C1-C3)

• Intrinsic Muscles:
  • Attach laryngeal cartilages to each other.
  • Act on vocal cords.
    • ADDucters (Close Rima Glottidis):
      • 1. Lateral CricoArytenoid:
        • Origin -> Lateral Cricoid Arch
        • Insertion -> Muscular process of Arytenoid
        • Nerve Supply -> (RLN)

• 2. InterArytenoid:
  • Only single intrinsic laryngeal Muscle.
  • Only Muscle receive bilateral nerve supply.
  • Origin -> Muscular process of Arytenoid
  • Insertion -> Muscular process of other Arytenoid
  • Nerve Supply -> (Bilateral RLN)

• 3. ThyroArytenoid (External Part):
  • Origin -> Inner surface of Thyroid angle.
  • Insertion -> Vocal process of Arytenoid
  • Nerve Supply -> (RLN)

• ABDuctor ( Open Rima Glottidis ):
  • 1.Posterior CricoArytenoid:
    • Only ABDuctor muscle.
    • Origin -> Posterior Cricoid Lamina
    • Insertion -> Muscular process o0f Arytenoid
    • Nerve Supply -> (RLN)

• Tensors:
  • 1. CricoThyroid:
    • Cheif pitch-changing muscle.
    • Only muscle seen on outside of Larynx.
    • Only muscle supplied by External SLN.
    • Origin -> Arch of Cricoid
    • Insertion -> Inferior horn and Lamina of Thyroid cartilage.
    • Nerve Supply -> (External SLN)

• 2. Vocalis (Internal Part of ThyroArytenoid):
  • Origin -> Inner surface of Thyroid angle.
  • Insertion ->Vocal process of Arytenoid
  • Nerve Supply ->(RLN)

References

Laryngeal electromyography: clinical application – https://pubmed.ncbi.nlm.nih.gov/19111439/

Pediatric laryngeal electromyography – https://pubmed.ncbi.nlm.nih.gov/22472235/

https://pubmed.ncbi.nlm.nih.gov/19111439/