[Comprehensive prognostic value of spontaneous and evoked electromyography in laryngeal paralysis].

OBJECTIVE

To determine the comprehensive prognostic value of spontaneous and evoked electromyography (EMG) in laryngeal paralysis.

METHODS

The characteristics of laryngeal EMG of 91 cases with unilateral vocal cord paralysis (VCP) after thyroid surgery were assessed. All cases were divided into four groups according to the interval of laryngeal EMG after onset, which were group one (2 months shorter, n = 13), group two (2 to 4 months, n = 23), group three (4 to 6 months, n = 36), group four (6 months longer, n = 19). The waveform morphology and the amplitude of laryngeal EMG and the highest evoked compound muscular active potential (CMAP) of thyroarytenoid muscles were examined and analyzed during voluntary tasks. The potential amplitude was showed by the percentage of that of the healthy lateral. The criterion of evaluation on evoked potential was attained by calculating statistical confidence interval.

RESULTS

The highest evoked CMAP in group one was significantly lower than that of the others (P < 0.05), but no significant difference was observed between group two and group three (P > 0.05), so group two and group three were analyzed together. There were 2 recovered cases and 11 unrecovered cases in group one. On the basis of this criterion that a positive prognosis for laryngeal recovery was indicated when the evoked CMAP presented and there was no misdirect generated potential, correct prognostic rate was 92% (12/13). There were 11 recovered cases and 48 unrecovered cases in group two and three. The highest evoked CMAP was much higher in the recovered than in the unrecovered, significant difference was observed between them (P < 0.001). On the basis of the criterion that a positive prognosis for laryngeal recovery was indicated when the highest evoked CMAP was higher than 26. 4%, correct prognostic rate was 90% (53/59). On the basis of the criterion that a positive prognosis for laryngeal recovery was indicated when there was no misdirect generated potential and the highest evoked CMAP was higher than 26.4%, correct prognostic rate was 93% (55/59). When the interval from onset to laryngeal EMG recovering was longer than 6 months, none of these patients had return of vocal cord mobility whatever were the outcomes of laryngeal EMG.

CONCLUSIONS

Correct prognostic rate can be improved if the prognosis of VCP in different courses is judged respectively by analyzing comprehensively spontaneous and evoked EMG.