The properties of laryngeal electromyography in the non-paralyzed sides of patients with idiopathic vocal cord paralysis.

Objective: To evaluate the injuries of the recurrent laryngeal nerve (RLN), superior laryngeal nerve (SLN), and their innervated laryngeal muscles on the non-paralyzed sides in patients with idiopathic vocal cord paralysis (IVCP).

Methods: Eighty-four cases of patients with IVCP were evaluated using stroboscopic laryngoscopy, voice analysis, and laryngeal electromyography(LEMG). Concurrently, twenty-eight cases involving healthy volunteers without vocal cord paralysis were enrolled and examined using LEMG during the same period. Subsequently, comparisons of LEMG results were conducted between the paralyzed and non-paralyzed sides, and among the non-paralyzed sides.Furthermore, a comparison was conducted between the LEMG results of the non-paralyzed sides in patients with IVCP and the corresponding ipsilateral sides in healthy volunteers.These comparisons were stratified based on the side of paralysis and the duration of the disease course (less than 3 months versus more than 3 months) for IVCP patients.

Results: Initially, the amplitude of the RLN, the action potential durations (APDs) and amplitude of the thyroarytenoid muscle (TM), and the amplitude of the posterior cricoarytenoid muscle (PCM) on the paralyzed side were significantly lower than those on the non-paralyzed side. Conversely, the latency of the RLN on the paralyzed side was significantly longer compared to the non-paralyzed side (P < 0.05). However, there were no significant differences in the latency and amplitude of the SLN, nor in the APD and amplitude of the CM between the paralyzed and non-paralyzed sides (P > 0.05). Furthermore, no significant differences were observed in the LEMG results of the non-paralyzed sides in IVCP patients, irrespective of the paralyzed side or the duration of the disease course (P > 0.05), and no significant differences of the LEMG results were observed when comparing the non-paralyzed sides of patients with IVCP to the ipsilateral sides of healthy volunteers (P > 0.05). However, when the disease course is less than 3 months, the amplitudes of the SLN and CM in the non-paralyzed side (right side) of left-sided IVCP patients are significantly lower than those in the non-paralyzed side (left side) of right-sided IVCP patients (SLN, 6.23 ± 4.42 mv vs. 10.21 ± 7.56 mv, t=-2.296, P = 0.028; CM, 0.49 ± 0.17 mv vs. 0.60 ± 0.19 mv, t=-2.207, P = 0.032), of which the amplitude of the CM is significantly reduced compared to the right side of healthy controls (0.49 ± 0.17 mv vs. 0.61 ± 0.21 mv, t=-2.423, P = 0.019), indicating that the SLN and CM on the non-paralyzed side are vulnerable to damage. Moreover, in patients with right-sided IVCP persisting for more than 3 months, there was a significant reduction in the amplitudes of the SLN and RLN, as well as the TM and PCM on the non-paralyzed side (left side), compared to the corresponding ipsilateral sides in healthy volunteers (P < 0.05). This observation indicates that the LEMG results for the non-paralyzed side in IVCP patients are not entirely normal, particularly in cases of right-sided IVCP with a disease duration exceeding three months.

Conclusion: In patients with IVCP, it is imperative to conduct a simultaneous analysis of LEMG results from both the paralyzed and non-paralyzed sides after determining the affected side and the progression of the paralysis. This thorough examination is crucial for accurately evaluating the condition and prognosis of individuals with IVCP.