Radiation as a treatment for malignant head and neck tumors can reduce the number of blood vessels in the treatment area and lead to scarring. In some cases, this can paralyze the vagus nerve, of which the RLNs are branches. Tumors of the vagus nerve, called vagal neurilemmomas, can also paralyze the vocal folds. Trauma
VF paresis can result from trauma to one of more laryngeal nerves during intubation, surgery (e.g. thyroidectomy, spine surgery, carotid endartectomy, vagal nerve stimulator implantation), injection of botulinum neurotoxin, or penetrating neck trauma. Thyroid disease
Causes of VF paresis also include diseases of the thyroid gland, such as hypothyroidism, goiter, and thyroiditis. Systemic neurologic diseases
Several neurological diseases can cause VF paresis including:

Myasthenia Gravis (MG), a rare neuromuscular autoimmune disease. MGs dominant characteristic is muscles weakness including facial, jaw, pharyngeal and laryngeal muscles. Charcot-Marie-Tooth (CMT), a neurological heredity disease that affects both motor and sensory functions. CMT affects the nerve cells and interrupts the transmission of nerve impulses as it concerns the axons and the myelination of the nerve cells. Multiple Sclerosis (MS), which is an autoimmune disease that damages the myelin sheet surrounding the axons of the cranial nerves and the spinal nerves. There are several types of MS depending on the course of the disease. Spinocerebellar Degeneration, a term that refers to a rare yet diverse chronic disease that affects the brain and the spinal cord.
Vocal cord paresis, also known as recurrent laryngeal nerve paralysis or vocal fold paralysis, is an injury to one or both recurrent laryngeal nerves (RLNs), which control all intrinsic muscles of the larynx except for the cricothyroid muscle. The RLN is important for speaking, breathing and swallowing.The primary larynx-related functions of the mainly efferent nerve fiber RLN, include the transmission of nerve signals to the muscles responsible for regulation of the vocal folds position and tension to enable vocalization, as well as the transmission of sensory nerve signals from the mucous membrane of the larynx to the brain. A unilateral injury of the nerve typically results in hoarseness caused by a reduced mobility of one of the vocal folds. It may also cause minor shortages of breath as well as aspiration problems especially concerning liquids. A bilateral injury causes the vocal folds to impair the air flow resulting in breathing problems, stridor and snoring sounds, and fast physical exhaustion. This strongly depends on the median or paramedian position of the paralyzed vocal folds. Hoarseness rarely occurs in bilaterally paralyzed vocal folds. Signs and symptoms
Typically, patients with vocal fold paresis or paralysis are able to identify the onset of their symptoms. The most commonly reported symptom patients with either vocal fold paresis or paralysis make is having a rough voice quality. It is important to note that the symptoms of vocal fold paresis are not specific to the condition and tend to be common symptoms of other voice disorders as well.