Is electrical muscle stimulation (EMS) effective for treating vocal cord paralysis?

Electrical Muscle Stimulation for Vocal Cord Paralysis

Electrical muscle stimulation (EMS) is not currently recommended as a standard treatment for vocal cord paralysis due to insufficient evidence supporting its effectiveness in improving morbidity, mortality, or quality of life outcomes in clinical practice. While some research shows promise in animal models and small human studies, current guidelines do not include EMS as a recommended intervention for vocal cord paralysis management.

Current Diagnostic and Management Approach

The American Academy of Otolaryngology-Head and Neck Surgery recommends a structured approach to vocal fold paralysis that does not include EMS 1:

1. Initial diagnosis: Laryngoscopy to confirm vocal fold paralysis
2. Imaging: From skull base to thoracic inlet to identify etiology
3. Prognostic assessment: Laryngeal electromyography (LEMG) between 21 days and 6 months post-onset

LEMG is valuable for:

• Differentiating between neurogenic and mechanical causes of immobility
• Providing prognostic information about potential recovery
• Identifying vocal fold paresis (partial paralysis) 1

Evidence Regarding Electrical Stimulation

Research Status

• Animal studies have shown promising results with functional electrical stimulation (FES):

  • In cats, FES of paralyzed thyroarytenoid muscle induced vocal fold adduction
  • Improved phonation time and voice intensity during vocalization 2
  • Restored adduction of the vocal fold and improved voice quality 2

• Human applications remain largely experimental:

  • A 2003 study with six patients using implantable stimulators showed potential for treating bilateral vocal fold paralysis 3
  • Selective electrical surface stimulation (SES) showed feasibility in a 2021 study with 32 unilateral vocal fold paralysis patients, with selective laryngeal response triggered in 87.5% of patients 4

Limitations of Current Evidence

• Most studies are small, non-randomized, and lack long-term follow-up
• Guidelines from the Neurolaryngology Study Group do not recommend EMS as a standard treatment 5
• No large-scale clinical trials have demonstrated clear benefits for morbidity, mortality, or quality of life

Clinical Considerations

Potential Applications

• Bilateral vocal fold paralysis may benefit more than unilateral cases 3
• Electrical stimulation parameters are critical:
  • For surface stimulation: pulse widths between 50-100ms with amplitude 7.1-7.2mA showed best results 4
  • For implantable devices: 1-2 second train of 1ms pulses at 30-40Hz and 2-7V amplitude 3

Pitfalls to Avoid

• Delaying proper diagnostic workup with laryngoscopy and imaging while pursuing experimental treatments 1
• Making permanent surgical decisions before determining if spontaneous recovery will occur 1
• Relying on EMS without addressing the underlying cause of vocal fold paralysis

Current Best Practice

Until more robust evidence emerges, management should follow established guidelines:

1. Confirm diagnosis with laryngoscopy
2. Identify etiology with appropriate imaging
3. Consider LEMG for prognostic information
4. Implement conventional treatments based on severity and impact on quality of life

EMS remains an investigational approach that may hold promise for future management of vocal cord paralysis but requires further research before becoming standard clinical practice.