What is the management for a patient with a vagal nerve stimulator (VNS) experiencing a persistent throat sensation?

Management of Persistent Throat Sensation in Patients with Vagal Nerve Stimulator

The persistent throat sensation in patients with vagal nerve stimulator (VNS) is most commonly due to laryngopharyngeal dysfunction from vagal nerve stimulation and should be managed by adjusting stimulation parameters under neurological supervision.

Pathophysiology and Prevalence

Laryngopharyngeal dysfunction is a common side effect of VNS therapy, occurring in approximately 66% of patients 1. This dysfunction typically manifests as:

• Persistent throat sensation/discomfort
• Hoarseness
• Dyspnea
• Coughing
• Voice changes with pitch breaks

These symptoms occur primarily due to stimulation of the inferior (recurrent) laryngeal nerve, which is a branch of the vagus nerve responsible for vocal cord function 1, 2.

Evaluation

When a patient with VNS presents with persistent throat sensation, the following evaluation should be performed:

1. Videolaryngoscopy: To assess vocal fold mobility and identify potential secondary supraglottic muscle tension and hyperfunction with reduced left vocal fold mobility 2

2. Voice assessment: Using tools such as the Voice Handicap Index and Maximum Phonation Time (MPT) to quantify voice changes 2

3. VNS settings review: Document current stimulation parameters (amplitude, pulse width, frequency, ON/OFF cycle)

4. Timing correlation: Determine if symptoms correlate with the ON cycle of stimulation

Management Algorithm

First-line Management:

1. Adjustment of VNS parameters (in consultation with neurology):

   • Reduce stimulation amplitude (typically 1.0-2.0 mA)
   • Decrease pulse width (standard is 500 μs)
   • Modify stimulation frequency (standard is 20-30 Hz)
   • Adjust duty cycle (standard is 30 seconds ON, 5 minutes OFF) 1

2. Voice therapy: For patients with confirmed vocal cord dysfunction to address secondary muscle tension patterns

Second-line Management:

1. Temporary deactivation: Consider temporarily deactivating the VNS to determine if symptoms resolve, confirming the relationship between stimulation and symptoms

2. Medication options:

   • For throat discomfort: Topical anesthetics or throat lozenges
   • For associated cough: Antitussives if appropriate

Third-line Management:

1. Surgical revision: If symptoms persist and significantly impact quality of life, surgical revision of the VNS lead placement may be considered 1

2. Device replacement or removal: In cases of intolerable side effects that cannot be managed with parameter adjustments 1

Important Considerations

• Timing of symptom onset: True vocal cord paralysis is rare (1-2.7%) and usually transitory, often caused by surgical trauma during implantation rather than stimulation itself 1

• Differential diagnosis: Rule out other causes of throat discomfort such as:

  • Postoperative hematoma (occurs in 1.9% of cases) 3
  • Infection (occurs in 2.6% of cases) 3
  • Lead malfunction (occurs in 3.0% of cases) 3

• Monitoring: Regular follow-up is essential to assess symptom progression and response to management strategies

Prognosis

Most laryngopharyngeal symptoms related to VNS are transitory and respond well to parameter adjustments. In a study of VNS complications over 25 years, vocal cord palsy occurred in only 1.4% of patients as a long-term complication 3. While persistent throat sensation can be uncomfortable, it rarely leads to serious complications such as aspiration 2.

Referral Considerations

• Otolaryngology: For videolaryngoscopy and management of laryngeal side effects
• Neurology: For VNS parameter adjustments
• Speech therapy: For voice rehabilitation in cases of significant voice changes

By systematically addressing the persistent throat sensation through parameter adjustments and appropriate specialist referrals, most patients can achieve significant symptom improvement while maintaining the therapeutic benefits of VNS therapy.