Changes in Saccular Function after Cochlear Implantation Presenter: Sarah King, AuD, CCC-A April 3, 2009 American Academy of Audiology Convention Acknowledgements Contributors: Lisa Cowdrey, MA, CCC-A Heidi Frazier, MS, CCC-A Sarah King, AuD, CCC-A Kristen Lewis, AuD, CCC-A IRB approval #08-286 by St. Luke s Hospital Institutional Review Board Background Cochlear Implantation (CI) is a widely accepted treatment method to restore hearing to persons with severe to profound hearing loss Over the years, candidacy criteria has become less restricted Cochlear Implant surgical risks have been minimized Vestibular System Injury after CI Many clinical and research studies have been carried out to determine the affects of CI surgery on balance function but results have been variable Enticott et al.: 32% of patients subjectively reported postoperative vestibular disturbance Buchman et al.: Literature Review Caloric data varies between 0% to 77% change in caloric function post-operatively Buchman et al. report a 38% change in caloric responses across all these studies Fina et al.: 39% of subjects had post-operative dizziness (Kim et al., 2008) (Enticott et al., 2006; Buchman et al., 2004; Fina et al., 2003) CI and Vestibular Injury Most post-operative dizziness is transient and short-lived Dizziness post-operatively is most commonly related to surgical trauma and/or vestibular system stimulation by the CI Histopathologic studies: Saccule is the most frequently damaged, followed by the Utricle, then the Semicircular Canals Otolithic disorders often present with symptoms of unsteadiness or stumbling Ernst et al. reports that otolithic vertigo is difficult to treat (Basta et al., 2008; Tien & Linthicum, 2002; Ernst et al., 2005) Vestibular Evoked Myogenic Potential (VEMP) Short latency electromyograms (EMG) that are recorded from the sternocleidomastiod muscle (SCM) Evoked by high level acoustic stimuli Measures saccule and/or inferior nerve function (Akin & Murnane, 2001)
Current CI/VEMP Research Melvin et al.: 31% of patients showed evidence of saccular damage 95% Confidence interval for saccular injury is 8-54% Krause et al.: 8/8 patients had change in VEMP 2 months post-operatively Only 3 of these 8 patients reported subjective vertigo post-operatively Current CI/VEMP Research Ernst et al.: 8/12 had loss of VEMP response at 1 year post-operatively Basta et al.: Airconduction vs. Boneconduction Pre-op: n=18, 15 subjects with normal AC/BC VEMP, 1 with BC VEMP only Post-op: No AC VEMPs elicited, 6 (37.5%) with normal BC VEMPs (Ernst et al., 2006; Basta et al., 2008) (Melvin et al., 2008; Krause et al., 2009) Current CI/VEMP Research Todt et al.: Round Window vs. Cochleostomy 50% of Cochleostomy group lost VEMP response, 13% of RW group lost VEMP response Concluded that RW insertion is less traumatic to vestibular receptors Jin et al. (2006, 2007) 7/12 (58.3%) had either an absent VEMP or decreased amplitude Found that some patients with absent post-op VEMP had a normal VEMP response with the cochlear implant device on (Todt et al., 2008; Jin et al., 2006; Jin et al., 2007) Importance of Balance Testing Because the vestibular system is at risk for injury, it is necessary to determine function pre-operatively Goal of surgery should be to preserve inner ear function, including hearing and balance function Our Study Based on the findings of these studies and the risk of saccular dysfunction, our clinic retrospectively reviewed our standard of care data Data Collection Began in 2007 Collected pre-operatively, 6 weeks postoperatively and 6 months post-operatively Procedure Otoscopy and tympanograms were performed prior to VEMP collection to confirm middle ear status VEMP Recording Parameters Epoch time: 53.3 ms 100 sweeps maximum Electrode montage 2 channel with binaural stimulation Active Electrode: Right and left SCM Inactive Electrode: Back of left hand Common Electrode: Mid forehead
Procedure VEMP Stimulus Parameters Binaural inserts 500 Hz toneburst Alternating polarity Begin at 95 dbnhl, dropping by 5 db to threshold VEMP Amplifier Parameters Gain: 5000 Artifact rejection off Low pass filter: 10 Hz High pass filter: 1500 Hz Subjects 38 subjects were included pre-operatively 17 implanted ears at 6 weeks 16 implanted ears at 6 months Mean Age: 53 yrs (range 12-86 yrs) Etiologies: unknown (n=13); NIHL (n=6); hereditary (n=4); measles (n=3); congenital (n=2); high fever (n=2); anatomical-eva, Mondini (n=2); sudden (n=2); Warrensburg's (n=1); Fabry Disease (n=1); Meningitis (n=1); Connexin 26 (n=1) Subject Ear Device Surgical Technique 1 L Advanced Bionics Round Window 2 R Cochlear Cochleostomy 3 L Cochlear Round Window 4 R Cochlear Round Window 5 L Advanced Cochleostomy Bionics 6 R Cochlear Round Window 7 L Med El Round Window 8 L Advanced Bionics Cochleostomy 9 L Cochlear Round Window 10 R Med El Round Window 11 L Advanced Round Window Bionics 12 R Cochlear Cochleostomy 13 L Cochlear Round Window 14 R Med El Cochleostomy 15 L Cochlear Cochleostomy 16 L Med El Cochleostomy 17 L Cochlear Round Window 18 R Med El Round Window 19 R Advanced Bionics Round Window 20 R Cochlear Round Window 21 R Advanced Bionics Round Window 22 R Cochlear Round Window 23 L Med El Cochleostomy 24 R Cochlear Cochleostomy Hybrid 25 L Cochlear Round Window 26 B Advanced Bionics Round Window 27 L Advanced Bionics Cochleostomy 28 L Cochlear Round Window Key: L = Left, R = Right, B = Binaural; Advanced Bionics = Advanced Bionics HiRes 90K; Cochlear = Cochlear Freedom (CI24RE); Med El = Med El Sonata; Cochlear Hybrid = Cochlear L24 Hybrid Patient Demographics Pre-operative Data 38 patients were tested pre-operatively and data was included 26 out of 74 (35.62%) ears tested preoperatively had no measurable VEMP 2 ears had a significant amplitude asymmetry (RE was 59.9%, 41% smaller) 6 weeks post-operatively Data Collected Mean 6.6 weeks (range 5.7 to 9.8 weeks) 17 normal VEMP ears that were implanted were tested at 6 weeks 6 ears (35.29%) with No Response 1 ear elevated threshold (15 db) 2 ears had significant asymmetries (56%;45%) with the implanted ear being smaller 7 ears with absent VEMP pre-op continued to be absent post-op 6 months post-operatively Data Collected Mean 28.3 weeks (range 24-32.6 weeks) 16 normal VEMP ears pre-op were tested at 6 months post-implantation 7 ears (43.75%) with no response post-op 1 ear had a significant asymmetry (44%) with the implanted ear being smaller 1 ear was absent at 6 weeks, then returned at 6 months but with 43% asymmetry (implanted ear smaller) 1 ear with increased thresholds returned to normal
Completed Data Sets Implanted Ears - Data Collected at all Intervals Pre-op 6 weeks 6 months Subject 1 Normal Absent Absent 6 Normal Elevated Threshold Normal 7 Normal Normal Asymmetry (44% smaller) 9 Normal Normal normal 10 Normal Absent Asymmetry (43% smaller) 11 Normal Absent Absent 12 Normal Normal Normal 13 Normal Absent Absent 14 Normal Absent Absent 16 Normal Absent Absent 17 Normal Asymmetry (45% smaller) Normal Discussion Surgical technique Round window vs. Anterior-Inferior Cochleostomy No significant difference between technique (Fisher s Exact Test; p = 0.63) Device Advanced Bionics HiRes 90K, Cochlear Freedom, Med El Sonata, Cochlear L24 Hybrid No significant difference between devices (Fisher s Exact Test; p = 0.32) Post-Operative Dizziness 8 patients reported short lived post-op dizziness ranging from mild to severe Discussion Age Contra-lateral Ear Analysis of VEMP response Presence/absence Amplitude Threshold Latency Timing of Data Collection Conclusions The risk of saccular dysfunction post-operatively at 6 months ranges from 28% to 72% with a mean of 50% (95% confidence interval) No conclusion about device, surgical technique or age can be made from our small sample size Clinical vestibular testing should be performed preoperatively Future research should focus on minimizing surgical damage to preserve both hearing and balance function Future Directions Stimulation of Vestibular System by Cochlear Implant 9 patients were tested at 6 months with device on vs. device off 2 ears had absent VEMP responses with the cochlear implant processor on / 1 ear had an elevated VEMP threshold (25 db) Things to consider: electrical interference, presentation of controlled stimuli to the processor, control for ambient noise, individual map parameters Control for Amplitude Monitor muscle contraction Use neck measurements to guarantee electrode placement is the same Thank you for your time! Sarah King, AuD, CCC-A sking@saint-lukes.org Dizziness questionnaire Use validated questionnaire to quantify subjective dizziness reports
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