Review of Audiology, Vestibular and Electrophysiology Tests

Audiology Testing

Audiology tests can provide information about hearing, middle ear function, cochlear hair cell function and several neural aspects of the hearing-balance system. Although there are many ear related conditions which cause hearing loss along with vertigo symptoms a complete audiological evaluation may help differentiate certain ear disease-disorders from one another. For example, Meniere’s disease and Labyrinthitis typically have both hearing loss and vertigo, whereas vestibular neuronitis and BPPV only have the symptom of vertigo. Audiology testing often includes: Pure tone (air and bone) and word discrimination tests as well as Immittence Audiometry which evaluates middle and inner ear and some neurological pathways. Otoacoustic Emissions is a relatively new test that looks at the outer hair cell function within the inner ear (cochlea). Brainstem Auditory Evoked Response (BAER) tests the neural conductivity of the hearing and balance nerve (CN VIII).

Sensory Organization Performance Test (SOP)

A combination of the Romberg, CTSIB and Fukuda Stepping Tests provide qualitative information on whether an equilibrium dysfunction exists, whether it is CNS or peripheral and also serves as an indicator of impact on balance function. Whether the patient is surface or visually dependent gives insight into the status of the vestibular system. Recovery of function post treatment may also be documented.

Computerized Dynamic Visual Acuity Test (CDVAT)

This protocol evaluates for oscillopsia. Oscillopsia is a breakdown in gaze stabilization during active head movement caused by peripheral or central vestibular disorders. The abnormal vestibular-ocular reflex (VOR) function of as little as 3 degrees can change vision from 20/20 to 20/200 with simple head movements. The vision test is conducted while the patient produces horizontal and then vertical head movement of 2.5 cycles per second. This is in low-mid range of normal active head movement. The test indicates the function problem caused by the vestibular dysfunction and can be used as a baseline to latter compare improvement post Vestibular Rehabilitation Therapy (VRT) to document the treatment efficacy.

Videonystagmography

The most enduring and commonly used test of vestibular function is the ENG. The test is comprised of subtests, which test the following:

Ocular-motor - Tests saccadic, pendular and optokinetic pursuit are tests which provide diagnostic information about the central vestibular and neuroopthamologic systems connection within the brain.

Gaze testing - Tests for the presence of spontaneous nystagmus.

Positional testing - Documents the presence of static positional nystagmus. Findings are used for differential diagnosis of HC-BPPV and other peripheral type causes vs. CNS lesions.

Dix-Hallpike - Tests for Benign Paroxysmal Positional Vertigo (BPPV-PC).

High Frequency Headshake - Dynamically provokes nystagmus in some cases if the patient has an uncompensated or non-stabilized unilateral vestibular dysfunction.

Caloric Testing - Thermal convection of inner ear fluids are created by irrigating each ear with warm and cool air. The reactivity or responsiveness of each of the respective ears horizontal semicircular canals is calculated through a measurement of the patient’s induced nystagmus. A difference of 25% or more in the total nystagmus of the two ears indicates a “caloric weakness” a finding usually attributed to a peripheral or central dysfunction. In some disorders, both ear’s responses are depressed.

Vestibular-Evoked Myogenic Potentials (VEMPS)

Vestibular Evoked Myogenic Potential, (VEMP) is based on the reflex, which occurs between the otolith system (specifically the saccule), and the sternocleidomastoid muscle. The vestibulo-collic reflex (VCR) has been well studied in animals and humans. The benefit of VEMPs is there is no other vestibular function test, which provides information regarding the saccule or its innervation by the inferior branch of the vestibular nerve.

As the VCR is a classic reflex arc with a sensory, CNS, and motor output component, it has been used to provide information regarding both the integrity of the saccule and inferior vestibular nerve, as well as the reflex arc through the brainstem. This has provided information on both otologic and neurologic conditions such as Meniere's, superior canal dehiscence syndrome to neurological disorders such as multiple sclerosis.