also use the term recurrent laryngeal nerve paralysis. additionally, superior laryngeal nerve damage (sln) can also lead to vocal fold paresis. the sln is responsible for sensory input to the vocal folds. due to its variable nature, the progression of vocal fold paresis may fluctuate, so it may be characterized differently from one evaluation to the next. fluctuating vocal fold paresis has been observed in neurodegenerative disorders like guillain–barré syndrome or myasthenia gravis. the posterior cricoarytenoid (pca) is a muscle of the larynx that is responsible for pulling the vocal folds apart from one another. vocal fold paresis describes the weakness of the pca and an impairment to its functioning. unilateral vocal fold paresis is the term used when there is damage to the rln on one side of the body. in unilateral vocal fold paresis, there is a lack of nerve supply to one side of the vocal fold's pca muscle. this lack of nerve supply renders the arytenoid cartilage immobile. the rln may be damaged during surgical procedures. the right rln in particular, has a greater chance of being damaged during surgery due to its position in the neck. when both of the vocal folds' pca muscles lack a nerve supply, the term bilateral vocal fold paresis is used. with bilateral vocal fold paresis, a person's airway may become blocked as the muscles are unable to pull the vocal folds apart fully. treatment the treatment of vocal fold paralysis varies depending on its cause and main symptoms. for example, if laryngeal nerve paralysis is caused by a tumor, suitable therapy should be initiated. in the absence of any additional pathology, the first step of clinical management should be observation to determine whether spontaneous nerve recovery will occur. voice therapy with a speech-language pathologist is suitable at this time, to help manage compensatory vocal behaviours which may manifest in response to the paralysis. voice therapy the overall goal of voice therapy is to narrow the glottis without causing hyperfunction of the surrounding muscles. in the past, forced adduction exercises were used to push the vocal folds together, but often resulted in additional stress on the vocal folds. current methods focus more generally on improving abdominal support, muscle strength and agility. hard glottal attacks hard glottal attacks involve building up subglottal pressure (air pressure below the vocal folds) before letting out a vowel sound. often, this method is beneficial for clients who compensate by use of a falsetto register. half-swallow boom the half-swallow boom allows for a repositioning of the vocal folds by taking advantage of laryngeal positioning when swallowing. the client is asked to take a breath and then initiate the movement of swallowing, followed by forcefully saying "boom". when performed properly, the "boom" sounds loud and clear. eventually, this sound can be generalized to other words and phrases. abdominal breathing training in breath support is essential for those clients who identify as professional voice users. shifting the awareness of the breath to the belly (diaphragmatic breathing) aids in efficient vocal function, reducing the risk of hyperfunction and muscular tension. lip and tongue trills lip and tongue trills aid in the balance of resonance, as well as coordinate the muscles of respiration, phonation and articulation. in addition, subglottal pressure may increase during lip trills, and result in the generation greater vocal fold vibration. surgery after 9 months of observation, should the paralysis not resolve and the patient be dissatisfied with the outcomes of voice therapy, the next option is temporary injection medialization. in this procedure, a variety of materials can be injected into the body of the vocal fold in order to bring it closer to the midline of the glottis. materials such as teflon, autologous fat, collagens acellular dermis, fascia, hydroxyapatite and hyaluronates are available to be used in the procedure. the choice of substance is dependent on several factors, taking into consideration the specific condition and preference of the patient as well as the clinical practice of the surgeon. the materials serve the purpose of filling up the vocal folds and increasing their volume. this allows the paralyzed vocal fold to make contact with the alternate fold, in order to more efficiently produce phonation. while injection augmentation has been long considered best practice, neither technique nor materials used have been standardized across clinicians. with this, results prove to be both safe and effective, but variable in their duration, lasting anywhere from 2 to 12 months. for patients with significant paralysis at 12 months post-onset, medialization thyroplasty may be suggested. this surgical procedure introduces a shim between the inner wall of the larynx and the soft tissue supporting the vocal fold. as a result, the paralyzed vocal fold is supported in a position closer to the midline of the glottis, and retains its ability to vibrate and phonate efficiently. in addition to medialization thyroplasty, arytenoid adduction can be performed to improve phonation results. this medical procedure consists of pulling the vocal processes of the arytenoid medially while monitoring the voicing quality being produced by the patient. when the best phonation appears to be achieved, the vocal processes are then maintained in place by a thread. a further surgical intervention used to mitigate vocal fold paresis is laryngeal reinnervation. this procedure restores nerve supply to the larynx and can be accomplished according to different techniques. depending on the specific condition (i.e. bilateral versus unilateral vocal fold paralysis), these techniques include reconnecting parts of the rln, supplying the laryngeal muscles with a donor nerve like the ansa cervicalis, or connecting the rln to a donor nerve. post-surgical outcomes in many cases, the surgical treatment options described above (temporary injection medialization, medialization thyroplasty, arytenoid adduction, and laryngeal reinnervation) have led to favourable outcomes as measured perceptually, acoustically, by laryngoscope, or via quality of life measures. however, none of these surgical interventions has been shown to be significantly better than the others. voice therapy after surgery it is generally recommended that voice therapy start 1 to 2 months after surgery, when swelling has subsided. post-surgical intervention is warranted to restore laryngeal muscle strength, agility and coordination. epidemiology due to the complex and controversial nature of this condition, epidemiological (incidence) reports vary significantly and more research in this area is needed. instead of reporting the incidence of this condition within the general population, most studies are conducted within specialized voice disorder clinics. in such a setting, one study found that approximately 26% of patients are diagnosed with paralysis or paresis of the vocal folds. yet, incidence rates as high as 80% for vocal fold paresis have been reported elsewhere. yet another source reported only 71 cases of vocal fold paresis over 7 years. incidence rates of vocal fold paresis after undergoing thyroid surgery have been reported between 0.3% and 13.2%, whereas these incidence rates are between 2% and 21.6% after undergoing spinal surgery.