Quantitative laryngeal electromyography assessment of cricothyroid function in patients with unilateral vocal fold paralysis.

OBJECTIVES/HYPOTHESIS Determination of superior laryngeal nerve (SLN) involvement in addition to recurrent laryngeal nerve (RLN) paralysis in patients with unilateral vocal fold paralysis (UVFP) relies on traditional, qualitative laryngeal electromyography (LEMG) examination. It is necessary to develop a quantitative measurement that reflects the degree of denervation of the cricothyroid (CT) muscle. The present study aimed to establish a standard quantitative assessment of CT function in patients with UVFP by measuring the turn frequency. STUDY DESIGN Case series study performed in an otolaryngology outpatient clinic. METHODS Twenty healthy subjects and 103 patients with UVFP were recruited. The main outcome measures for the patients included acoustic analysis using traditional LEMG examination, quantitative LEMG analysis, and acoustic analysis based on fundamental frequency contours. RESULTS Acoustic reliability was examined in the healthy subjects, and the peak fundamental frequency in an upward glissando showed good test-retest reliability, especially for the offset fundamental frequency. LEMG indicated that 33 patients had RLN and SLN lesions (RLN+SLN group) and 70 had only RLN lesions (RLN group). When patients produced a standard upward glissando sound, the peak turn frequency reflecting the recruitment of the CT muscle was significantly lower in the RLN+SLN group compared with the RLN group (406±256 vs. 778±238 Hz; P<.001). CONCLUSIONS We conclude that quantitative measurement of the interference pattern when voicing a standard upward glissando sound may provide a feasible reflection of the degree of a SLN injury. LEVEL OF EVIDENCE 4.