The Role of Cervical and Ocular Vestibular Evoked Myogenic Potentials in the Assessment of Patients with Vestibular Schwannomas

Abstract

ObjectivesTo investigate the clinical utility of VEMPs in patients suffering from unilateral vestibular schwannoma (VS) and to determine the optimal stimulation parameter (air conducted sound, bone conducted vibration) for evaluating the function of the vestibular nerve.MethodsData were obtained in 63 patients with non-operated VS, and 20 patients operated on VS. Vestibular function was assessed by caloric, cervical and ocular VEMP testing. 37/63 patients with conclusive ACS ocular VEMPs responses were studied separately.ResultsIn the 63 non-operated VS patients, cVEMPs were abnormal in 65.1% of patients in response to AC STB and in 49.2% of patients to AC clicks. In the 37/63 patients with positive responses from the unaffected side, oVEMPs were abnormal in 75.7% of patients with ACS, in 67.6% with AFz and in 56.8% with mastoid BCV stimulation. In 16% of the patients, VEMPs were the only abnormal test (normal caloric and normal hearing). Among the 26 patients who did not show oVEMP responses on either side with ACS, oVEMPs responses could be obtained with AFz (50%) and with mastoid stimulation (89%).ConclusionsThe VEMP test demonstrated significant clinical value as it yielded the only abnormal test results in some patients suffering from a unilateral vestibular schwannoma. For oVEMPs, we suggest that ACS stimulation should be the initial test. In patients who responded to ACS and who had normal responses, BCV was not required. In patients with abnormal responses on the affected side using ACS, BCV at AFz should be used to confirm abnormal function of the superior vestibular nerve. In patients who exhibited no responses on either side to ACS, BCV was the only approach allowing assessment of the function of the superior vestibular nerve. We favor using AFz stimulation first because it is easier to perform in clinical practice than mastoid stimulation.

Assessment of the Clinical Utility of Cervical and Ocular Vestibular Evoked Myogenic Potential Testing in Elderly Patients

“…It is possible that the observed increase in VEMP threshold in older people (4,18,23Y25) is due to decreased sensitivity of the end organ to sound pressure but not to linear acceleration including gravity. This possibility is supported by recent findings showing a smaller age effect on VEMPs elicited with bone-conducted vibration and with mechanical taps, which produce linear acceleration, compared with air and bone conduction stimuli (4,6,26). cVEMP and oVEMP are helpful tools for researchers trying to understand the underlying physiology of the vestibular system.…”

“…Others have shown that AC is not the most reliable stimulus and does not produce the most robust responses (4,6,13). For example, Chiarovano et al (6). observed that bone conduction was a more effective stimulus in that it was more likely to produce a measureable response in individuals with vestibular schwannomas.…”

Sustained and Transient Vestibular Systems: A Physiological Basis for Interpreting Vestibular Function

“…The asymmetrical VEMPs are preserved for many years and probably permanently after the vestibular loss (92, 101–103). The clinical value lies in realizing that one cannot rely on the results of one of the tests of otolith function: the test of static otolithic function—OCR—which may show symmetrical responses indicating normal otolithic function, whereas in the same patient, the VEMPs may show the loss of transient otolithic function and so identify the patient’s problem (95, 104). …”

Clinical Utility of Ocular Vestibular-Evoked Myogenic Potentials (oVEMPs)

“…Reliable monitoring of these usually slowgrowing tumors is important, as 'watchful waiting' may be an appropriate strategy in some patients [64]. Along with measures of canal function, both oVEMPs and cVEMPs are often attenuated or absent in patients with tumors affecting the vestibular nerve or cerebellopontine angle [65][66][67][68][69]. Chiarovano at al.…”

“…Chiarovano at al. evaluated the clinical utility of VEMPs in patients with nonoperated VS [65]. They found that BC oVEMPs were abnormal in 68% of the patients, while AC cVEMPs were abnormal in 65%, and the oVEMP was the only abnormal test in some of the patients.…”