MRI of head MRA
CT scan of temporal bone ELECTROPHYSIOLOGY
LABORATORY PROCEDURES FOR DISORDERS RELATED TO THE EIGHTH NERVE Indication
Suspect fistula, cholesteatoma, mastoiditis, congenital abnormality
FLUID AND TISSUE ANALYSIS
Lyme titers Glyco-Hgb ANA TSH
Otoacoustic emissions VESTIBULAR TESTING ENG
Fistula test Posturography OTHER TESTS
Ambulatory event monitoring Holter monitoring Tilt table testing
Post-traumatic vertigo Vertigo with disturbed consciousness Asymmetrical hearing loss Central hearing disturbance
Tick bite with hearing symptoms or vertigo Meniere's symptom complex Meniere's symptom complex Meniere's symptom complex Central hearing disturbance Malingering
Vertigo, hearing symptoms
Secondary test for Meniere's and perilymphatic fistula Infant hearing screening
Bilateral vestibular loss Ototoxin exposure
Secondary test to confirm abnormal ENG
MRI, magnetic resonance imaging; MRA, magnetic resonance angiogaphy; CT, compued tomography; EEG, electroencephalogram; BAER, brain stem evoked responses; MLR, middle lattency response; FTA, fluorescent treponemal antibody; glyco, glycoselated; Hgb, hemoglobin; ANA, antinuclear antibody; TSH, thyroid stimulating hormone; ECOG, electrocochleography; ENG, electronystagmography; TIA, transient ischemic attack; CVA, cerebrovascular accident response to intense sound, and they can be helpful in corroborating particular types of hearing loss. Reflexes that are present at abnormally low levels suggest recruitment with a cochlear site of lesion. Reflexes that decay rapidly suggest a retrocochlear lesion.
The word recognition score (WRS) (also called speech discrimination) measures the ability to repeat words presented at a comfortable loudness. Word recognition can be impaired by both auditory distortion and central abnormalities such as a nonfluent aphasia. Speech reception threshold (SRT) measures the auditory threshold of hearing for words. It should be consistent with pure-tone hearing. When they are not consistent, a nonperipheral hearing disturbance is more likely.
The short-increment sensitivity index (SISI), alternate binaural loudness balance (ABLB), and Bekesey's tests are no longer used in most clinical practices. Audiometry is particularly useful in the diagnosis of Meniere's disease. A fluctuating low-tone sensorineural hearing loss is typical of this condition ( .Fig, 12-6 ).
Otoacoustic emissions have become an added option to the hearing evaluation. A click is usually used to generate the response. The outer hair cells generate a sound in response to the stimulus, and this sound is captured by a microphone in the ear canal. The test has proven useful for infant hearing screening.
Four types of vestibular tests are selected according to the clinical situation. Electronystagmography (ENG) is the most useful, and it consists of a battery of procedures that can identify vestibular asymmetry (such as that caused by vestibular neuritis) and that document spontaneous or positional nystagmus (such as that caused by BPPV). Because of anatomical variability and technical difficulty, the ENG result can be misleading, most commonly suggesting an abnormality when none exists. An abnormal result that does not fit the clinical picture should be confirmed with rotatory chair testing. Rotatory chair testing measures vestibular function of both inner ears together and is also highly sensitive and specific for bilateral loss of vestibular function. Although rotatory chair testing does not establish the side of a unilateral vestibular lesion, there is a characteristic pattern on unilateral loss. For this reason it can also be helpful in corroborating an abnormal ENG. Fistula testing involves the recording of nystagmus induced by pressure in the external ear canal. Its sensitivity to a perilymph fistula is only 50 percent, but it is the only objective procedure that is available to substantiate a clinical suspicion of fistula. Posturography is an instrumented variant of the Romberg's test. The sole diagnostic indication for posturography at this writing is to document malingering.
Syncope is a common differential diagnosis in the evaluation of disorders of cranial nerve VIII; it is sometimes useful to check patients for arrhythmia or abnormal control
Figure 12-6 Audiogram depicting the low-tone sensorineural loss typical of Meniere's disease. The gray shaded area indicates the normal range. The lefX marks) is normal at all frequencies. The right ec(circles) has decreased hearing on both air and bone for lower frequencies.
of blood pressure. Ambulatory event monitoring or Holter monitoring is used to detect arrhythmia or sinus arrest. Tilt-table testing is sometimes advocated for the diagnosis of syncope. At present, however, this is a lack of data establishing a link between tilt-table test abnormalities and successful treatment outcomes, and thus the role of the tilt-table test in the evaluation of dizzy patients is presently unclear.
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