Figure 1.
Presentation of the five VEMP tests.
Cervical VEMPs (mostly saccular function) are induced by air-conducted sounds through headphones using either 500 Hz short-tone burts (AC STB) or high level clicks. Ocular VEMPs (mostly utricular function) are evoked by either AC STB delivered through headphones, or bone-conducted vibration through a mini-shaker applied at AFz (AFz BCV) or at the mastoid (mastoid BCV). The sign + indicates the stimulated ear and the grey banner corresponds to the site of recording. Cervical VEMPs are composed of two early waves: P13 and N23 (scale bar: 100 µV). Ocular VEMPs are composed of two early waves, n1 and p1, with smaller peak-to-peak amplitudes (scale bar: 5 µV).
Table 1.
Means (±SD) peak-to-peak amplitude of cVEMPs induced by AC STB and clicks, and mean (±SD) peak-to-peak amplitude of oVEMPs induced by AC STB and BCV (AFz and mastoid), in healthy subjects, 63 patients with non-operated VS (affected and intact side) and 20 patients after surgery for VS (intact side).
Table 2.
Mean (±SD) latencies of cVEMP induced by STB and clicks (P13 and N23) and of oVEMPs induced by AC STB and BCV (AFz and mastoid; n1 and p1), in healthy subjects, 63 patients with non-operated VS (affected and intact side) and 20 patients after surgery for VS (intact side).
Table 3.
Number (%) of non-operated VS patients (n = 63) exhibiting abnormally weak (decreased or abolished) response from the affected side or normal responses to vestibular tests (ACS cVEMPs, AC STB and BCV oVEMPs, and caloric tests).
Table 4.
Number (%) of responder non-operated VS patients (n = 37) exhibiting abnormal decreased response, abnormal abolished response from the affected side (EPr = 100%) or normal response to vestibular tests (ACS cVEMPs, AC STB and BCV oVEMPs, and caloric tests).
Figure 2.
Clinical utility of VEMP test in vestibular schwannoma patients.
This patient has a right VS in the cerebello-pontine angle. Despite the size of the VS (MRI in A), he had both normal hearing and caloric test results. Patient had superior nerve dysfunction (absence of AC STB cVEMP on the right SCM when the right ear was stimulated: B) and inferior nerve dysfunction (abnormal AC STB oVEMPs on the left eye when the right ear was stimulated: C). When the left intact ear was stimulated, normal AC STB cVEMPs (D) and normal AC STB oVEMPs (E) were observed.
Table 5.
Results for six VS patients with abnormal cervical and/or ocular VEMPs but normal caloric and hearing tests.
Table 6.
Number (%) of operated VS patients (n = 20) with abnormal responses or no responses on either side to VEMP tests.
Figure 3.
Flowchart showing the oVEMP results for non-operated VS patients (n = 63).
Results are presented according to the following test sequence: AC STB, AFz BCV and mastoid BCV. This sequence is optimal to provide reliable conclusions about the functional status of the inferior (mostly utricular) nerve in a minimum of time. Patients with normal ACS oVEMPs always exhibited normal AFz and normal mastoid oVEMPs (Figure 3, grey squares). Patients with abnormal oVEMPs also exhibited abnormal AFz (25 of 28 patients) and abnormal mastoid oVEMPs (21 of 28 patients) (Figure 3, purple squares). Abnormal ACS but normal BCV oVEMPs were observed in three of 28 patients for AFz and in seven of 28 patients for mastoid BCV (Figure 3, yellow squares). Among the 26 ACS NR patients, 13 were NR for AFz BCV and three were NR for mastoid BCV(green squares).
Figure 4.
Flowchart illustrating in which order the stimulations (ACS and BCV) should be done to test predominantly the function of the superior and mostly of the utricular nerve using oVEMPs.
IVN: inferior vestibular nerve - SVN: superior vestibular nerve. ACS stimulation may be performed first in patients suffering from vertigo. If ACS induced normal oVEMPs, BCV was not required. If ACS gave abnormal oVEMPs, bone stimulation should be done. We suggest beginning with AFz BCV stimulation: this mode stimulates both labyrinths equally and is easier to perform than mastoid stimulation in a routine clinical setting. When no response was observed on either side to ACS and to AFz stimulation, mastoid BCV stimulation is necessary to appreciate the residual function of the superior vestibular nerve.