A novel technique for clinical assessment of laryngeal nerve conduction: normal and abnormal results.

OBJECTIVES/HYPOTHESIS: To describe a novel conduction study of the laryngeal nerves, including normal values and abnormal findings.

STUDY

DESIGN

Prospective nonrandomized.

METHODS

Seventeen healthy adult volunteers, as well as three patients with clinically identified laryngeal neuropathy, underwent low-level brief electrical stimulation of the laryngeal mucosa by means of a wire inserted via a transnasal flexible laryngoscope. Bilateral hookwire electrodes recorded the result in the laryngeal adductor muscles.

RESULTS

This study yields an early response ipsilateral to the side of stimulation (LR1), which is uniform and consistent (right = 13.2 ± 0.80 msec; left = 15.2 ± 1.20 msec), and late bilateral responses (ipsilateral LR2 [LR2i] and contralateral LR2 [LR2c]), which exhibit greater variation in latency and morphology (right LR2i = 50.5 ± 3.38 msec; left LR2i = 52.2 msec; right LR2c = 50.7 ± 4.26; left LR2c = 50.6 ± 4.07). Findings in abnormal patients differ significantly from normal, consistent with the distribution of neuropathy.

CONCLUSIONS

We describe a novel, clinically applicable conduction study of laryngeal nerves. Normative electrodiagnostic values and variations of the reflex responses of the laryngeal adductor muscles in response to irritative stimulation of the laryngeal mucosa (Laryngeal Closure Reflex) are proposed. By enabling the determination of electrophysiological parameters of the superior laryngeal and recurrent laryngeal branches of cranial nerve X (CN X), this procedure, which is used as an adjunct to laryngeal electromyography, may provide earlier and more accurate information regarding the extent and grade of nerve injury. Because injury grade relates directly to prognosis, the information derived from this test may have clinical relevance in determining optimal treatment.