Neural Monitoring of the Superior Laryngeal Nerve in Thyroid Surgery
Condition: Laryngeal Nerve; Thyroid Surgery
MeSH terms: Thyroid Diseases
Study type: Interventional

Summary: 
      Thyroid surgeons place an enormous amount of importance and rightly so to the preservation of
      the recurrent laryngeal nerve (RLN) during thyroidectomies. A good knowledge of the anatomy
      of the nerve and meticulous dissection technique and intraoperative identification of the
      nerve are crucial to the anatomic and functional integrity of the nerve. The use of
      intraoperative neural monitoring to aid the surgeon in the identification of the RLN has
      gained acceptance and is considered standard practice in several units. However, lesser
      emphasis has been placed historically on the identification and preservation of the external
      branch of the superior laryngeal nerve (EBSLN) during thyroid surgery. The EBSLN supplies the
      cricothyroid muscle that controls pitch variation during phonation. Unlike damage to the
      recurrent laryngeal nerve which manifests readily as vocal cord paralysis, intraoperative
      damage to EBSLN is difficult to assess postoperatively as visual assessment of the larynx is
      not indicative of the integrity of the nerve. Injury of the EBSLN can cause weakness or
      complete paralysis of the ipsilateral cricothyroid muscle. Patients may report a deeper voice
      or an inability to produce high pitched sounds.

      Patients may also complain of weakness, tightness of the voice, and require extra effort to
      speak. Of note, voice changes with EBSLN injury are subtle in the general population but can
      be devastating in patients who depend on their voice for a living. Importantly, EBSLN injury
      is reported in upto 50% of thyroid surgery in contrast to 12% of recurrent laryngeal nerve
      injury during thyroid surgery. The new guidelines published in the Laryngoscope recommend
      routine intraoperative neural monitoring of EBSLN. The Investigators have a functional system
      in use currently for monitoring recurrent laryngeal nerve intraoperatively and propose to
      study the impact of monitoring the EBSLN using the same neural monitoring device to improve
      voice results following thyroid surgery.
    

Detailed description: 
      Thyroid surgery can result in change in the voice. This is because two nerves controlling the
      voice quality are situated very close anatomically to the thyroid gland and are at risk of
      damage during the surgery. One of the nerves that is called the recurrent laryngeal nerve
      controls the movements of the voice cords and is more readily identifiable and its injury is
      also detected easily by direct examination of the voice box as reduced/absent movement of the
      voice cord. It gets damaged in upto 1% of thyroid surgeries. The other nerve that is of
      interest to our study is called the superior laryngeal nerve, and its external branch (EBSLN)
      controls the pitch of the voice cord by supplying a muscle called the cricothyroid. This
      nerve is difficult to see and is reported to be damaged in 50% of thyroid surgeries. Its
      damage cannot be picked up on direct examination of the larynx and voice changes are subtle
      though devastating for individuals who depend on their voice for their livelihood singers
      actors etc. The Investigators would like to study if using a nerve monitor that is used to
      check the RLN during thyroid surgery can also be used to check the EBSLN. The Investigators
      hope that this could reduce the chances of damaging the nerve significantly. If the study
      shows good preservation of the EBSLN with the nerve monitor the Investigators will be able to
      make it a standard procedure during thyroid surgery.

      The Investigators plan to recruit patients undergoing thyroid surgery involving one half of
      the thyroid gland. They will be given all the information about the study and consent will be
      obtained. If they agree to participate they will be divided into two groups randomly those
      who will have the intraoperative EBSLN monitoring and those who will not. All patients will
      have a preoperative voice assessment in the speech therapy unit which will involve filling in
      a voice questionnaire and undergoing a glottography (pitch assessment) They will then undergo
      the surgery Approximately 3 months after the surgery they will have another voice assessment
      using the voice questionnaire and the glottography. At this time they will also have an EMG
      assessment of the cricothyroid muscle which is the best method to check the function of the
      EBSLN. No further procedures/assessments will be undertaken.
    

Intervention name(s): Monitoring
Intervention type(s): Procedure
Intervention description(s): intraoperative EBSLN monitoring
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Prevention