What are the indications, contraindications, risks, and interpretation of laryngeal electromyography (EMG) for evaluating unexplained vocal‑fold immobility?

Laryngeal Electromyography for Unexplained Vocal Fold Immobility

Laryngeal EMG has a definitive role in diagnosing disorders of vocal fold movement and distinguishing neurological paralysis/paresis from mechanical causes of immobility, though its evidence base remains limited primarily to guiding botulinum toxin injections. 1

Primary Indications

Laryngeal EMG is indicated for:

• Diagnosis of vocal fold paralysis/paresis – Distinguishing neurological impairment from mechanical causes of immobility (joint fixation, arytenoid dislocation, tumor bulk effect) 1, 2, 3, 4
• Guiding botulinum toxin injections into laryngeal muscles – This remains the only indication with robust evidence support from the 2004 evidence-based review 1
• Differentiating between neurological and mechanical vocal fold immobility – EMG shows normal parameters in arytenoid dislocation but abnormal findings in true paralysis 4
• Prognostic assessment following recurrent laryngeal nerve injury, though data are limited and caution is advised for early management decisions 1

Contraindications and Limitations

LEMG has NOT been validated for:

• Upper motor neuron disorders involving the larynx 1
• Spasmodic dysphonia diagnosis 1
• Vocal tremor diagnosis 1
• Muscle tension dysphonia 1
• Malingering or psychogenic dysphonia 1

Common pitfall: The diagnostic validity of LEMG for these movement disorders remains unknown despite ongoing clinical use. 1

Technical Standardization

The American Academy of Otolaryngology-Head and Neck Surgery recommends specific electrode types for different purposes: 1

• Concentric needles – Provide uniform field for motor unit action potential (MUAP) waveform analysis 1
• Monopolar needles – Useful for guiding botulinum toxin injection 1
• Bipolar hooked wires – Useful for multiple muscle recordings and repetitive tasks 1

A multidisciplinary team of an otolaryngologist and electromyographer is recommended for diagnostic LEMG. 1

Basic Examination Protocol

Standard muscle sampling should include: 1

• Thyroarytenoid/lateral cricoarytenoid complex bilaterally – Comparing affected versus unaffected sides 1
• Cricothyroid muscle bilaterally – Comparing affected versus unaffected sides 1
• Additional muscles as clinically indicated based on presentation 1
• Adequate sampling of insertional activity 1

Interpretation Criteria for Neuropathy

Multiple criteria must be used with concordant abnormalities across several aspects: 1

• Multiple samples (2-3 different locations per muscle) are needed to evaluate recruitment, spontaneous activity, and fibrillation potentials 1
• Commonly available diagnostic equipment does not usually provide accurate quantitative assessment for laryngeal muscles 1
• LEMG is currently a qualitative, not quantitative examination in clinical practice 1

Key EMG patterns include: 2

• Normal pattern – Normal recruitment and motor unit potentials 2
• Neuropathy pattern – Reduced recruitment, fibrillation potentials, positive sharp waves 2, 3
• Myopathy pattern – Distinct from neuropathic changes 2

Clinical Utility Data

Recent evidence demonstrates variable clinical impact:

• LEMG changed medical treatment plans in 27% of patients with laryngeal motion abnormalities 5
• LEMG guided or confirmed treatment course in 32.4% of patients 5
• LEMG did not change treatment in 40.5% of patients 5
• In pediatric vocal fold immobility, LEMG showed 100% sensitivity and 92% specificity for diagnosing paralysis versus other causes 4

Quantitative parameters showing promise: Amplitude and frequency of motor unit potentials correlate with return of vocal fold functionality and may predict neural recovery 6

Risks and Practical Considerations

LEMG is an invasive procedure requiring needle insertion into laryngeal muscles, which has limited its widespread use, particularly in pediatric populations. 4

Critical caveat: Most published LEMG reports are Class IV retrospective non-blinded case series, representing low-quality evidence. 1 Prospective blinded studies are needed to determine true sensitivity, specificity, and reliability. 1

For symptomatic patients with suspected vocal fold paresis: Unblinded qualitative LEMG studies found neuropathy in 19/22 cases (86%), suggesting motion abnormalities likely reflect neurological impairment. 1 However, blinded studies are needed to confirm diagnostic accuracy. 1

Prognostic Value

Limited evidence exists for LEMG's prognostic capability in predicting recovery from acute unilateral vocal fold paralysis following recurrent laryngeal nerve injury. 1 While advocated by some practitioners, caution should be applied when using LEMG findings for early management decisions. 1

Serial EMG recordings can monitor recovery and establish prognosis by tracking reinnervation patterns, particularly useful in traumatic nerve injuries. 4