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Cochlear Implantation On Vestibular Function Health And Social Care Essay

发布时间:2017-04-17
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Cochlear implantation (CI) has enabled hearing rehabilitation of deaf patients for more than 20 years. The overwhelming worldwide success has increased the indication for CI in recent years which, now includes patients with preserved residual hearing, infants, unilaterally deaf patients with severe tinnitus and bilateral CI that sometimes simultaneous (Krause et al. 2009). Moreover, many implant candidates often have aidable preoperative hearing in the ear for implantation, and it has been recognised that combined electrical and acoustical hearing may improve performance of the cochlear implant (Enticott et al. 2006). Therefore, the development of CI popularity raises the necessity of recognize and when possible prevent associated risks and side effects.

Although the risk caused by CI to the vestibular system remains unclear, the intervention requires surgery to the inner ear, and has usually caused the loss of residual hearing and, in some patients, loss of vestibular function (Enticott et al. 2006). One possible complication of CI is the impairment of balance function with resulting vertigo symptoms. Its incidence reported in the literature varies quite widely from 0.33% to 75% (Steenerson et al. 2001; Buchman et al. 2004; Krause et al. 2009). Transient acute dizziness is common after cochlear CI, but the long-term disability due to vestibular dysfunction after unilateral CI showed low incidence (Chiong et al. 1994; Brey et al. 1995; ITO 1998; Steenerson et al. 2001; Fina et al. 2003; Enticott et al. 2006; D. Basta et al. 2008; Buchman et al. 2004).

Many studies have tried to characterize the effects of CI on the vestibular system by using perioperative questionnaires, vestibulo-ocular reflex (VOR) testing, caloric irrigations, rotational chair testing, platform posturography, vestibular-evoked myogenic potentials (VEMP) as well as other less commonly used tests. The variance in these reports and others may be the result of factors such as retrospective study design, subjective nonvalidated questionnaires applied in a nonstandardized way, lack of both pre- and postoperative testing of patients, and study of different patient populations, devices types, programming strategies, surgical procedures, and testing paradigms. Because a large number of CI candidates may have significant vestibular impairment before implantation as a result of underlying inner ear pathology, the perceived effect of CI on vestibular function may be underestimated (Buchman et al. 2004).

Vestibular examination has also been suggested as a useful tool for predicting an optimal outcome, as well as for avoiding a possible bilateral areflexia in case of a contralateral areflectic ear (Huygen et al. 1995; Filipo et al. 2006). Hence, when hearing threshold measurement does not give sufficient information for distinguishing between the two ears (i.e. bilateral profound hearing loss), a thorough vestibular workup could give indirect but reliable information regarding which ear is working better. Filipo et al. (2006) mentioned that, the harmful potential of CI on a labyrinthine structure with residual function is further stressed by the observation of a high incidence (19-31%) of vestibular impairment reported when CI was performed on the better hearing ear (Ribári et al. 1999; Backous & Quigley 2000; Szirmai et al. 2001).

The likelihood of the cochlea being systematically damaged during CI surgery derives from the fact that its lateral wall and fluid spaces are directly violated by the surgical procedure (i.e. during the cochleostomy and the insertion of the electrode lead inside the scala tympani) (Filipo et al. 2006). Tearing of the basilar membrane by the electrode lead, with consequent mixture of labyrinthine fluids and loss of inner ear anatomo-functional integrity, has been indicated as one of the possible harmful mechanisms (Huygen et al. 1995). Therefore, several conservative approaches have been developed recently, pursuing soft surgery techniques, minimal cochleostomy, and short electrode carriers (Filipo et al. 2006).

Handzel et al. (2006), from a temporal bone collection of human implantees, showed a high incidence of cochlear hydrops and saccule collapse affecting more than half of the CI patients. They concluded that hydrops might be the consequence of damage to the lateral cochlear wall rather than obstruction of the membranous labyrinth, which may explain the pathogenesis of delayed-onset attacks similar to Meniere's disease affecting some implant patients (Handzel et al. 2006). Furthermore, it is important to consider the influence of the ongoing electrical stimulation and its duration (time from surgery) as due to simultaneous stimulation of both auditory and ectopic vestibular fibres or to the presumed cross-stimulation phenomenon (Filipo et al. 2006).

According with Krause et al. (2009), the major cause of vestibular disorder after CI seems to be the trauma caused by the insertion of the electrode into the inner ear, which can lead to an intraoperative loss of perilymph, foreign body reaction or labyrinthitis, postoperative perilymph fistula, and endolymphatic hydrops. On the other hand, an electrical vestibular stimulation by the implant, an autoimmune Menière syndrome, a Tullio phenomenon, and a benign paroxysmal positional vertigo, seems to be rare.

Vestibular dysfunction causing balance disturbances after surgery can take individuals weeks to months to recover as central vestibular processes adapt for the disturbance (Steenerson et al. 2001; Fina et al. 2003; Enticott et al. 2006). However, the true incidence of damage to the inner ear structures caused by unilateral CI surgery may be masked by central compensation of unilateral vestibular hypofunction. Redundancy of the two labyrinths and plasticity of the central nervous system create a fault-tolerant system, so that even after unilateral labryrinthectomy, most patients regain a nearly normal vestibulo-ocular reflex (VOR) for all head movements except quick rotations and translations toward the injured labyrinth (Cremer et al. 1998; Melvin et al. 2009). In contrast, acute loss of bilateral vestibular function can cause significant disability because of VOR failure, postural instability, and chronic disequilibrium. As the popularity of simultaneous bilateral and second CI increases, it is crucial to understand the risk of iatrogenic vestibular hypofunction (Melvin et al. 2009).

Dizziness after CI usually develops as a result of vestibular hypofunction. Recently, benign paroxysmal positional vertigo (BPPV), which is a hyperfunctioning form of vestibular dysfunction, has been reported as a complication of surgical procedures that involves the cochlea such as stapedectomy and CI (Limb et al. 2005; Viccaro et al. 2007). This could be because of direct trauma (tip of the piston) or indirect trauma (vibration induced by the drill). Also, electric current spread during CI stimulation could induce the dislodging of the otolith (Di Girolamo et al. 1999). Despite these hypotheses, the incidence and the time of onset of BPPV symptoms do not always coincide with a definite postsurgical period or with the immediate activation of CI (Viccaro et al. 2007).

  Viccaro et al. (2007) study demonstrated 10% of BPPV incidence in CI patients of versus 2.2% reported in other studies in the literature. They believed that the high incident may be due to the methodology used in the study - prospective analysis, characterized by scrupulous instrumental assessment of vestibular features, in all patients, before and after cochlear implantation. Thus, the findings described in this study cannot be compared with those of retrospective studies appearing in the literature. Although their study did not find common risk factor (age, type of implant, cause of deafness and anatomic differences in the cochlea and labyrinth), all the patients with BPPV after CI were women.

Three different theories have been proposed in the literature to explain the occurrence of BPPV in patients with CI. The first theory (Limb et al. 2005) refers to the creation of bone dust particles during cochleostomy, which may fall into the labyrinth via a micro rupture in the basilar membrane and, travel into the endolymphatic compartment reaching the lumen of the semicircular canal, thus producing canalolithiasis and leading to the onset of BPPV. The second theory (Limb et al. 2005), the vibration caused by a drill on the cochlea would be enough to dislodge several otoconias into the labyrinth, causing canalolithiasis. The third theory (Di Girolamo et al. 1999) refers to the dislodging of otoconias due to the electric stimulation that occurs during the initial fitting; the first fitting session might thus have a triggering effect (Viccaro et al. 2007).

There are many types of dizziness occurring after CI that has been described in the literature. One type occurs in the immediate postoperative period and might present either as an acute attack of vertigo (Fina et al. 2003) or as mild episodes of transient imbalance similar to BPPV that are related to postural changes and head movements (Kubo et al. 2001). Early-onset dizziness is probably related to the surgical trauma of the procedure manifesting as acute vestibular injury. Another type of dizziness after CI occurs in a delayed fashion (Kubo et al. 2001; Fina et al. 2003). This type dizziness occurs in episodes lasting several hours and is usually is associated with hearing fluctuation (function of the implant) (Fina et al. 2003) and tinnitus that similar to Meniere's disease symptoms.

Limb et al. (2005), suggested that the theory of bone dust particles travelling to posterior SCC would explained the delayed-onset BPPV and. On the other hand, the theory of the dislodging of otoconia during surgery caused by drill vibration, would explained the immediate-onset postoperative BPPV after CI. Furthermore, the fact that onset of symptoms appears to be irrespective of implant activation argues against an electrical explanation for CI-associated BPPV. Moreover, the association with head movements also argues against an electrical mechanism. Their study did not find risk factors for the occurrence of BPPV after CI, however, all the identified cases were women.

According with Enticott et al. (2006), patients aged 70 years and older had significantly greater incidences of permanent vestibular damage after implant surgery as demonstrated by the caloric results, and this was not related to the position of the intracochlear electrode or operating surgeon. These results suggested that the older ear is more prone to permanent injury as a result of cochlear implant surgery, however, there is needed further study into the susceptibilities of other inner ear suborgans and the actual cause of trauma from implant surgery.

Vestibular symptoms are variously reported among patients undergoing CI. Several studies have aimed to determine incidence of vestibular dysfunction after implantation and investigate why this damage occurs. However, the risk caused by CI to the vestibular system remains unclear. The aim of this thesis is to systematically review the literature and with the use of an evidence base, clarify some important aspects of the effects of CI on vestibular function thus providing some basis for better pre and post vestibular assessment as well as preoperative counselling and postoperative vestibular therapy to cochlear implants patients.

METHOD

Aims and hypothesis

Subjects

Stimuli or materials, questionnaires etc.

Task

RESULTS

DISCUSSION

CONCLUSIONS

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