Abstract
Objective
1) Measure vestibular function before and after cochlear implantation (CI) using a battery of tests covering the full range of stimulus frequencies over which the normal angular vestibulo-ocular reflex (VOR) stabilizes gaze.
Methods
Semicircular canal (SCC) function was assayed using head impulse test during 3-dimensional scleral search coil eye movement recordings (HIT), dynamic visual acuity during rapid head movements (DVA), head-shake nystagmus (HSN), and caloric electronystagmography (ENG). Saccular function was determined using vestibular-evoked myogenic potentials (VEMP). Patient self-assessment via the dizziness handicap inventory (DHI) and clinical head impulse testing (cHIT) were also measured.
Results
One of 28 post-implanted ears (4%) suffered severe loss of vestibular function in all 3 SCCs. HSN revealed no change in 11 subjects. ENG revealed new hypofunction in 1 of 16 ears (6%). Passive DVA revealed no significant change for 16 implanted ears. VEMP revealed significant increase or disappearance in threshold in 5 of 16 ears (31%). DHI scores were variable and correlated poorly with objective tests. The cHIT performed by one otolaryngologist in 14 subjects exhibited 44% sensitivity and 94% specificity for detection of severe hypofunction confirmed via quantitative HIT.
Conclusions
CI carries a small but nontrivial risk of iatrogenic vestibular hypofunction in the implanted ear. For bilateral simultaneous-CI, the risk of bilateral vestibular hypofunction is ∼0.16%, comparable to the likelihood of meningitis. The cHIT was highly specific for vestibular hypofunction in this study, but likely depends heavily on the examiner's threshold for abnormal.
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