Background: Temporary recurrent laryngeal nerve (RLN) palsy after thyroidectomy is usually due to a neurapraxia. Voice changes after thyroidectomy, in the absence of RLN palsy, are common. We postulated that this is due to edema and consequent increased diameter of the RLN during thyroidectomy. The aim of this study was to document changes in the diameter of the RLN during surgery.
Methods: A consecutive series of 110 RLNs was prospectively analyzed in 75 patients. The RLN was measured on identification and removal of the lobe. Electromyogram (EMG) amplitudes were recorded concurrently after neurostimulation. Univariate and multivariate analyses were performed.
Results: The mean increase in RLN diameter was 0.71 from 1.95 mm (P < 000.1). Right and left RLNs were similar diameter. On univariate and multivariate analysis, factors predictive of increased RLN diameter were increasing age (P = 0.04) and increased difference in EMG amplitude (P = 0.01). There was a mean increased EMG amplitude of 101 from 493.5 μV (P < 0.001). On univariate and multivariate analyses, factors predictive of increased difference in EMG amplitude were decreasing age (P = 0.01) and increased difference in RLN diameter (P = 0.02). There was a statistically significant positive relationship between increased diameter of RLN and increased EMG amplitude (R(2) = 0.04). The temporary RLN palsy rate was 3%.
Conclusions: The small numbers of temporary RLN palsies prevent correlation with increased diameter of RLN. However, this may explain voice changes after thyroidectomy without RLN palsy. The observed increase in RLN diameter is probably due to edema; its cause is unknown. The increased EMG amplitude seen with increasing RLN diameter may reflect increased excitability of ionic channels in neurons.