Investigations
1st investigations to order
audiogram
Test
Useful to document the extent of hearing loss and to confirm the affected ear. Subtle hearing loss can manifest itself on an audiogram.[4]
Result
An acute unilateral sensorineural hearing loss accompanying the vertigo may indicate labyrinthitis; hearing is not affected in vestibular neuritis.
Weber's test
Test
Bedside examination with a Weber 512-Hz tuning fork (placing the tuning fork on the forehead or maxillary teeth and asking the patient to state in which ear the sound was louder) can quickly localise the affected ear and determine whether the hearing loss is sensorineural or conductive.[37]
The sound will be perceived in the affected ear when a unilateral conductive hearing loss is present or in the unaffected ear when there is a unilateral sensorineural hearing loss.
The result of this test is combined with the result of the Rinne's test to interpret the type of hearing loss.[37]
Result
An acute unilateral sensorineural hearing loss accompanying the vertigo may indicate labyrinthitis; hearing is not affected in vestibular neuritis.
Rinne's test
Test
Allows the examiner to determine whether any hearing loss is secondary to middle ear (conductive hearing loss) or inner ear/eighth cranial nerve (sensorineural hearing loss) causes.[37]
The base of a 512-Hz tuning fork is placed on the mastoid, and the patient indicates when he or she no longer hears the sound. Once the sound is no longer audible, the tuning fork is placed in front of the ear and the patient is asked whether he or she hears the sound. If the sound is louder when the tuning fork is on the mastoid, then the patient has a conductive hearing loss. If the sound is louder with the fork in front of the ear, the hearing loss is sensorineural or normal.[37]
Result
An acute unilateral sensorineural hearing loss accompanying the vertigo may indicate labyrinthitis; hearing is not affected in vestibular neuritis.
Investigations to consider
CT or MRI brain
Test
Imaging can help to rule out differential diagnoses.
If a stroke is suspected, brain imaging (non-enhanced CT or MRI) should be ordered (at most within 1 hour of arrival at hospital).[45] Most acute strokes would not be picked up by CT, but a normal CT scan does not rule out a stroke - particularly in the first few hours. There might be a delay on MRI, but a normal diffusion-weighted MRI scan is very unlikely if the patient has had a stroke.[46]
If a temporal bone fracture is suspected, a CT scan of the head can delineate the extent of the fracture.[47] Most patients presenting with isolated symptoms suggestive of labyrinthitis may present without further contributory history of presenting illness to guide diagnostics. Thus, once stabilised clinically in the acute setting and rule-out of time-sensitive diagnoses like stroke, further work-up may be warranted to assess or rule out potential contributors to their symptoms. MRI or CT scans of the head can reveal inner ear malformations and temporal bone neoplasms. A CT scan may also be useful in patients with suspected superior semicircular canal dehiscence (SSCD), and also to assess the extent of disease in cases of a superimposed infection with cholesteatoma, given the right clinical picture to suggest these conditions, with the caveat that acute prolonged vertigo would be atypical in SSCD and would typically present in this manner only with a concurrent superimposed infection in cholesteatoma.[48][49]
Any patient with an asymmetric hearing loss should undergo a retrocochlear evaluation with gadolinium-enhanced MRI to investigate other causes of hearing loss. Labyrinthine enhancement on gadolinium-enhanced MRI in the setting of meningitis is a significant predictor of hearing loss.[50]
Result
may be normal or abnormal
videonystagmography (VNG)
Test
VNG is a computerised, non-invasive test that measures eye movements using infra-red goggles.[51] It can measure nystagmus as low as 0.5 degrees.[51] VNG helps identify whether balance or dizziness is due to vestibular disease and provides objective values regarding inner ear function. Abnormal results indicate inner ear disorders, such as labyrinthitis and vestibular neuritis.
Result
abnormal
head impulse testing (HIT) and video head impulse testing (vHIT)
Test
HIT helps identify peripheral vestibular deficits.[52] In this test, patient’s head is briskly rotated to record the instantaneous compensatory eye movement response.[52][53] The test can be performed in a room with normal lighting, as visual stimuli do not affect the outcomes.[53] Presence of nystagmus can interfere with the outcomes of bedside HIT.[52]
The output is measured as vestibulo-ocular response (VOR) gain. Healthy individuals have VOR gain close to 1, whereas patients with unilateral vestibular loss have a reduced VOR gain (usually <0.7).[53] Different VOR gains have been noted in patients with labyrinthitis and vestibular neuritis.[54]
vHIT is a modified form of HIT that identifies overt and covert saccades.[55][56][57] The vHIT involves a high-speed head-mounted camera on tight-fitting goggles with head velocity sensors; a software is used for accurate objective measures of the head and eye velocity.[53] The vHIT can evaluate VOR during relatively rapid head rotation and can individually measure the function of each semicircular canal.[53][54] One systematic review has reported a mean VOR gain of 0.48 ± 0.14 in the ipsilesional ear and >0.80 in the contralesional ear for patients with acute vestibular neuritis tested with vHIT.[57]
Acute vestibular neuritis most often affects both vestibular nerve divisions - superior and inferior.[25] Horizontal vHIT can identify superior nerve dysfunction, whereas vestibular evoked myogenic potentials and posterior vHIT can aid in the diagnosis of inferior vestibular nerve involvement.[25][58]
Result
usually <0.7 in patients with unilateral vestibular loss
rotary chair test
Test
Sinusoidal harmonic acceleration or rotating chair testing involves a variety of measurements of nystagmus on a patient who is rotated from side to side during the procedure in a computer-controlled chair.[59][60]
May provide additional information on vestibular compensation.
Result
may be normal or abnormal
vestibular-evoked myogenic potentials (VEMPs)
Test
Assess the electrical activity in the muscles in response to intense, brief auditory stimuli. VEMPs can help identify whether the dysfunction is related to the superior, the inferior, or both branches of the vestibular nerve.[61] A reduction in VEMP response upon stimulation of the affected ear may indicate vestibular neuritis or labyrinthitis.[26]
Cervical VEMPs are recorded from the sternocleidomastoid muscles, and ocular VEMPs are recorded from the inferior oblique extraocular muscles.[26][62][63] Most common stimulation methods include air-conducted sound, bone-conducted vibration, head taps, and, impulsive lateral acceleration.[62] An absent or reduced air-conducted and bone-conducted ocular VEMP in the presence of a preserved air-conducted cervical VEMP is a common finding in vestibular neuritis.[26]
Result
abnormal
syphilis serology
Test
Additional serological testing may be warranted if the presentation is atypical or if the patient has additional risk factors.[42]
Positive titres suggest syphilis is the cause of acute or recent deterioration in hearing.
Result
may be normal or abnormal
cerebrospinal fluid Gram stain and culture
Test
Patients with labyrinthitis secondary to bacterial meningitis should have appropriate cerebrospinal fluid studies and cultures performed.
Gram-negative diplococci suggest meningococcal infection in patients with a compatible clinical illness and may provide a rapid presumptive diagnosis.
Gram stains are positive in 30% to 80% of patients with culture-confirmed meningococcal meningitis.[64][65]
Result
gram-negative diplococci in presence of bacterial meningitis
serum HIV rapid test
Test
False-negatives may occur during window period immediately after infection before antibodies to HIV have formed. A positive result should be confirmed with a second rapid test.
Result
positive in HIV infection
basic metabolic profile (including urea and creatinine)
Test
For patients who have severe nausea and vomiting, a basic metabolic panel should be obtained before and after intravenous hydration therapy to monitor response.
Result
may be normal or abnormal
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