This is a case study for acute vestibular neuritis (VN) affecting the left superior vestibular nerve.
VN can affect both the superior and inferior vestibular nerves or just one. If a patient has superior nerve VN they are more likely to develop secondary benign paroxysmal positional vertigo (BPPV) than if both nerves are affected. Identifying this can help prepare the patient to be on the lookout for BPPV symptoms and know what to do if they occur. Superior, inferior or total vestibular neuritis can be eloquently identified using our test battery.
Video head impulse test (vHIT)
The vHIT is a nonintrusive, quick way of assessing horizontal semicircular canal (SCC) function. This test provides an objective measure of the vestibulo-ocular reflex in the horizontal canal plane. The horizontal SCC is innovated by the superior vestibular nerve and therefore we expect the response to be abolished by VN on the affected side.
Result interpretation: Head movement to the left is shown in blue, head movement to the right is red and green is eye movement. The right graph shows the green (eye movement) overlays the red (head movement to the right). This means that the eye is able to maintain gaze on a target by moving at the same speed in the opposite direction to the head.
On the left the green (eye movement) does not overlay the blue (head movement to the left). This means the eye is slipping off the target when the head is moved and a corrective saccade is being made back to the target after the head movement (red spikes). The eye movement is measured as gain. Normal gain is > 0.80 for this test. For this case the gain is 0.37 on the left consistent with left horizontal SCC dysfunction.
Vestibular evoked myogenic potentials (VEMPs)
VEMPs are an effective way to assess saccule and utricle function. They use sound or vibration pulses to activate the otolith organs. Stimulation of the vestibular system with air-conducted sound activates predominantly saccular afferents which is measured from the sternocleidomastoid muscles. The “cervical VEMP” (cVEMP) is thus a manifestation of the vestibulo-collic reflex. Bone-conducted vibration of the vestibular system activates a combination of saccular and utricular afferents, which is recorded from the extraocular muscles. These “ocular VEMPs” (oVEMPs) are a manifestation of the vestibulo-ocular reflex.
The utricle is innovated by the superior vestibular nerve and therefore we expect the response to be abolished by VN on the affected side.
The graph is blue which means the responses were recorded in the left channel. Up the top you see LI which means ipsilateral – the responses were recorded from under the left eye. The next is LC which means contralateral – the responses were recorded from under the right eye.
However, this is a crossed response, therefore the left eye (LI) is recording the response from the right utricle and vice versa. No response is recorded from under the right eye (LC) which is consistent with left utricle dysfunction.
The saccule is innovated by the inferior vestibular nerve, therefore we do not expect there to be an absent response for superior nerve VN.
On the graph you can see equal responses for the left (blue) and right (red). For this test, a significant interaural asymmetry is > 40%. If we see this, we like to confirm this asymmetry by performing bone-conduction cVEMPs. We will also do a bone-condition cVEMP if air-conduction responses are absent (common in our older patients).
We record ocular motor function tests and positional testing with an infrared camera. Below is an example of gaze testing to the centre. This first 20 seconds is with visual fixation where the patient focuses on a dot in front of them. The next 20 seconds is without visual fixation, where a cover is placed over the goggles.
In this example of left-sided superior nerve VN, there is spontaneous right beating nystagmus which is consistent with an acute left vestibular dysfunction. There is also spontaneous up beating nystagmus which raises the suspicion of central pathology. However in this case it is related to the anterior and posterior SCCs. The left anterior SCC (innovated by the superior vestibular nerve) is dysfunctional while the left posterior SCC (innovated by the inferior vestibular nerve) is persevered. These canals are in the vertical plane and the dysfunction of the left anterior SCC is creating an imbalance that shows up as up beating nystagmus.
Conversely acute inferior nerve VN would show a down beating nystagmus without visual fixation. Gaze testing is also performed with the eyes 30 degrees to the left and right. For this patient nystagmus was present in all three conditions which is called a tertiary nystagmus.
Audiometry and Auditory Brainstem Response
In VN the auditory nerve is not affected and therefore audiometric and ABR results will be normal or consistent with expected age-related loss.