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.[18]
Result
sensorineural hearing loss
Weber's test
Test
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.
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.[19]
Result
sensorineural hearing loss
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.[19]
The base of a 512-Hz tuning fork is placed on the mastoid and the patient indicates when he or she 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.
Result
sensorineural hearing loss
Investigations to consider
CT or MRI brain
Test
Imaging can help to rule out differential diagnoses.
If an acute stroke is suspected, a CT scan of the head can identify infarction and provide enough information to make decisions about acute management.[23] A subsequent MRI of the head with diffusion-weighted imaging can determine the extent of the infarct. If a temporal bone fracture is suspected, a CT scan of the head can delineate the extent of the fracture.[24] MRI or CT scans of the head can reveal inner ear malformations and temporal bone neoplasms. A CT scan of the petrous temporal bones may show evidence of middle-ear or mastoid opacification, and should be ordered if mastoiditis is suspected. A CT scan may be useful in patients with suspected superior semi-circular canal dehiscence, and to confirm cholesteatoma.[25][26]
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.[27]
Result
may be normal or abnormal
electronystagmography
Test
Records eye movements and responses to ocular and vestibular stimuli.
May provide additional information on vestibular compensation after the patient has recovered from the acute stage of labyrinthitis.
Warm and cold air or water placed in the ear canal may show that the affected ear has a less-robust response to caloric stimulation than the good ear.
Comparing results obtained from various sub-tests of an electronystagmography evaluation assists in determining whether a disorder is central or peripheral.[28]
Result
may be normal or abnormal
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.[28]
May provide additional information on vestibular compensation after the patient has recovered from the acute stage of labyrinthitis.
Result
may be normal or abnormal
vestibular-evoked myogenic potentials
Test
Uses an intense, brief auditory stimulus to assess the saccule ipsilateral to the stimulus.[29]
May provide additional information on vestibular compensation after the patient has recovered from the acute stage of labyrinthitis.
If the saccule or posterior semi-circular canal is affected, the vestibular-evoked myogenic potential amplitude may be lower in the affected ear.
Result
may be normal or abnormal
syphilis serology
Test
Additional serological testing may be warranted if the presentation is atypical or if the patient has additional risk factors.[22]
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.[30][31]
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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