Vocal cord paralysis is usually caused by damage to the vagus nerve or the recurrent laryngeal nerve.
As the vagus and recurrent laryngeal nerves travel a long distance in the body, when the tissue surrounding these nerves becomes diseased, invades, compresses or strains these nerves, it easily affects the function of the nerves there and causes vocal cord movement disorders. In malignant tumours, direct invasion of the vagus or recurrent laryngeal nerve by the tumour causes vocal fold paralysis, while in benign tumours, compression or strain on the vagus or recurrent laryngeal nerve causes vocal fold paralysis.