Limitations of the study
This study aimed at assessing the consistency of clinicians evaluating the movement of the vocal cord on a rating scale. “Worst case scenario” clinical situations were used, where the clinician had no history from the patient and was unable to hear the patient’s voice when they assessed the video of vocal cord movement. There was no extra information asked on the numerous other clinical findings that are seen in patients with vocal fold paralysis such as arytenoid prolapse, posterior gap, height and length mismatch. The wide variation in interrater scores for the 5 point scale may be related to the fact that there was no accompanying clinical history or sound with the videos, making it an artificial situation. Madden et al, when assessing consistency of vocal fold motion, included sound with their videos and they demonstrated higher inter-rater reliability, suggesting that a “complete picture” is required when assessing vocal cord movement. All the endoscopies performed were fibreoptic flexible nasendoscopy, which rendered poorer video quality than newer generation distal chip views, possibly making the more subtle movement of the vocal cords more difficult to judge and categorise. However, the videos very much reflected the reality of seeing patients in clinics and wards.
Conclusion
This study demonstrates quantitatively that it is challenging to accurately and consistently grade subtle differences of vocal cord movement as proven by lesser agreement and reliability when using a 5 point scale instead of a 3 point scale. Therefore, it highlights the need to have an objective measure to improve the accuracy of assessment of vocal cord movement. Image processing of endoscopy videos could be employed for measurement of vocal cord movement symmetry to quantify the degree of vocal cord motion, thus providing a reliable measure to assist in diagnosis and evaluate post treatment outcomes.