Investigations
1st investigations to order
audiometry
Test
Hearing loss is the most common cause of tinnitus.
Result
sensorineural or conductive hearing loss
Investigations to consider
FBC
Test
Test is ordered in all unrecognised cases of pulsatile tinnitus, as anaemia causes a hyperdynamic circulation that results in objective tinnitus.
Result
may show anaemia
thyroid function tests
Test
Test is ordered if aetiology of tinnitus cannot be determined, in cases of objective tinnitus (both patient and examiner can hear the noise of which the patient complains), and in patients who have tinnitus associated with pathognomonic symptoms of hyper- or hypothyroidism.
Hyperthyroidism causes a hyperdynamic state that can cause pulsatile tinnitus. Severe hypothyroidism can cause sensorineural hearing loss with associated tinnitus.
Result
hyperthyroidism or hypothyroidism
lipid profile
Test
Hyperlipidemia can cause an inner ear stroke and sudden hearing loss, which would in turn cause tinnitus.
Result
elevated cholesterol
fasting glucose
Test
Diabetes mellitus can cause sensorineural hearing loss with associated tinnitus.
Result
elevated in diabetes mellitus
fluorescent treponemal antibody absorption assay
Test
Tertiary syphilis can cause sensorineural hearing loss with associated tinnitus.
Result
positive in syphilis
MRI head
Test
Ordered in all patients with unilateral sensorineural hearing loss and normal physical examination.
Also ordered in patients with pulsatile tinnitus suspected to have arteriovenous malformations (AVMs) or glomus tumour.
MRI with gadolinium is the best test for tumours of the internal auditory canal and cerebellar pontine angle.
Result
high-riding jugular vein; stenotic carotid artery; AVMs; tumour
CT temporal bones
MR angiography or CT angiography
Test
Ordered in patients with pulsatile objective tinnitus.[35]
Result
arteriovenous malformations; arteriovenous fistulas; aberrant carotid artery; fibromuscular dysplasia; glomus tumour
carotid angiography
Test
Performed when MRI and MR angiography fail to diagnose a lesion and pathology is highly suspected.
This test is rarely needed.
Result
carotid stenosis; fibromuscular dysplasia
auditory brainstem response (ABR)
Test
An acoustic transducer creates a click via an earphone; the elicited response is detected by surface electrodes.
Evaluates waves I, III, and V primarily, which relate to the eighth cranial nerve, the inferior olive, and the inferior colliculus, respectively.
Should be considered in cases of unilateral tinnitus or unilateral hearing loss to exclude a tumour, multiple sclerosis, or other neural causes.
Limitations of the ABR include significantly reduced reliability of the test in patients who have >60 dB of hearing loss at 2000 hz, and a 22% false negative rate for vestibular schwannomas that are smaller than 2 cm.
Result
comparison of right and left side waveforms; positive result if the difference is outside of statistical norm
minimal masking level
Test
Can also be used for follow-up of treatment to find out whether the tinnitus has changed.
Result
minimum level of external tone that makes the tinnitus tone inaudible
residual inhibition
Test
The sound is heard by the patient for 1 minute, and then the patient should report any change in intensity of tinnitus. The sound that decreases tinnitus intensity by 100% is noted. The first tone offered is usually minimal masking level +10 dB.
Result
amount of noise that is able to suppress tinnitus
loudness and pitch matching
Test
This test is performed by matching the loudness and pitch of an administered tone to the perceived tinnitus tone of the patient.[36]
Result
pitch and loudness of the patient's tinnitus
loudness discomfort level testing
Test
This test is usually performed only in patients who have reduced loudness tolerance.[36]
Result
threshold level of discomfort for a sound
Emerging tests
otoacoustic emissions
Test
Assesses outer hair cell mobility and emissions are often absent or reduced in patients with conductive or sensorineural hearing loss. May see abnormalities with specific medications that could be reversible after elimination of the offending medication.
Result
reduced or absent emissions
functional MRI
Test
Brain activity can be measured and observed.
Result
enhanced neural activity in central auditory system
PET scan
Test
Brain activity can be measured and observed.
Result
enhanced neural activity in central auditory system
magnetoencephalographic
Test
Non-invasive measurement of magnetic activity of the brain that can show significant changes in patients with tinnitus.[38]
Result
increased activity in the auditory cortex and cochlear pathways
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