If you suspect that you are suffering from gentamicin poisoning (also called vestibulopathy/bilateral vestibulopathy/vestibulotoxicity/bilateral ototoxicity) and have talked with your primary care physician who tells you to go see an ENT…STOP. Whether or not you believe there is a chance that medical negligence was involved in your care, you need to be evaluated by an expert in the filed of otolaryngology and balance disorders, as soon as possible. You will want to find a neuro-otologist or otolaryngologist or a doctor of audiology to perform a complete vestibular work up. If your doctor is not familiar with a practitioner or facility that can perform this complete work up, you can visit vestibular.org and input your city/state to find testing as well as vestibular rehabilitation facilities.
PLEASE NOTE: THIS IS A SUMMARY OF VARIOUS TYPES OF VESTIBULAR TESTING. AN EXAMINER MAY OR MAY NOT UTILIZE ALL TESTS TO RENDER A VESTIBULAR FUNCTION DIAGNOSIS.
In-house (office) vestibular testing:
Dix-Hallpike Maneuver - This test is the most well-known of office vestibular testing. It is used to provoke nystagmus and vertigo commonly associated with BPPV BBPV (Benign paroxysmal positional vertigo) is not the same as bilateral vestibulopathy, and is not related to gentamicin and/or aminoglycoside toxicity. Individuals with classic BPPV symptoms can be treated with an Eply maneuver and may not need further vestibular testing.
Head Shake Nystagmus – This test is performed to evaluate asymmetry in the vestibular ocular reflex. The person is instructed to tilt his or her head down 30 degrees to allow maximal stimulation of the horizontal canal and told to shake the head back and forth as quickly as possible for a period of 30 seconds. Immediately following cessation of movement, the eyes are opened and observed for nystagmus. Persons with unilateral vestibular dysfunction will have unopposed stimulation of the intact labyrinth which results in a slow-phase to the side of the lesion and a rapid nystagmus to the intact side. This response is usually brief. No nystagmus is expected in normal subjects.
Head Thrust Test – This test is used to evaluate for unilateral vestibular function. In this test, the person’s head is turned 15-30 degrees from center and then rapidly rotated to the other side with them focusing on the examiner’s eyes. Persons with unilateral vestibular weakness will have a catch-up saccade when rotated rapidly to the side of the lesion. This test is rapidly and easily performed and can identify unilateral weakness of the vestibular system and as such is very useful clinically.
Dynamic Visual Acuity – This simple test can be used to sort out persons with bilateral vestibular weakness when chair testing is unavailable. With this test, an individual is asked to read the lowest line possible on a Snellen eye chart to establish a baseline visual acuity. This is followed by asking the individual to do the same task while rotating the head back and forth at a rate of 1-2 Hz. Loss of one line is considered normal, whereas loss of two-three lines suggests vestibular weakness. This test should be abnormal in persons with bilateral vestibular weakness and can be used to diagnose these challenging individuals.
Eye Movements – When testing cranial nerve function, an examiner should evaluate for smooth pursuit. Persons with erratic eye movements and saccades in various directions should be evaluated for CNS, specifically cerebellar dysfunction.
Romberg Testing – In this test, the individual is asked to stand with feet together with arms folded around the chest or at the side. Then the person is asked to stand like this with eyes open, and the amount of sway is compared to the same action with eyes closed. Individuals with equal sway have proprioceptive or cerebellar lesions. More sway with eyes closed suggests vestibular lesions, most commonly with sway to the side of vestibular weakness. The test can be performed with foot next to toe to make the test more difficult and to bring out more subtle weakness.
Fukuda Stepping Test – In this test, the individual is asked to march in place with eyes closed and arms held out forward. In the original test, Fukuda had individuals march 100 steps. Individuals with vestibular weakness will rotate to the side of the weak labyrinth 45 degrees or more with 100 steps. Shorter versions of the test can be used to observe lesser amounts of rotation.
Orthostatic Hypotension – Many persons with the complaint of dizziness will have the diagnosis of orthostatic hypotension causing “light headedness.” Orthostatic hypotension is a reduction of systolic blood pressure of at least 20mm HG or diastolic blood pressure of at least 10mm HG within three minutes of standing. This can be found in asymptomatic individuals, but in persons with corresponding vertigo and drop in blood pressure, the diagnosis is reinforced. Symptoms of orthostatic hypotension include lightheadedness, blurred vision, weakness, fatigue, cognitive impairment, nausea, palpitations, tremulousness, headache, neck ache, and dizziness.
Tandem Gait Testing – Walking heel to toe in a circular pattern requires intact cerebellar function and as such is used by some examiners to screen for cerebellar dysfunction. The specificity of this examination is low because many causes other than cerebellar dysfunction may cause poor performance on tandem walking tests.
Vestibular laboratory tests:
This battery of tests is used to help assess the function of your vestibular system. The vestibular system, comprising of your inner ear and associated nerves, is part of a complex system that helps control eye movements and balance. Measurement of certain eye movement can help determine how well the vestibular system is functioning.
ENG is the most widely used vestibular tests by an otolaryngologist and relies on the vestibulo-ocular reflex to test the peripheral vestibular function and its ability to generate efficient voluntary eye movements necessary for maintaining visual contact with the environment. It consists of three subtests or subgroupings of tests: 1) oculomotor tests, 2) positional and positioning tests, 3) caloric tests.
The ENG begins with a calibration test in which the individual is asked to follow a dot on the wall, usually laser generated, that moves in a sinusoidal pattern to allow calibration of the eye movements with the monitor recording. In addition, gaze evoked and spontaneous nystagmus are evaluated. It is important to note that these eye movements can be more accurately evaluated by ENG due to the possibility of recording eye movements with closed eyes or with Frenzel glasses which eliminate visual fixation, and therefore suppress the nystagmus.
Oculomotor tests – this first subdivision of ENG is evaluated by saccadic tracking, smooth pursuit tracking, and optokinetic tracking. The common thread of these tests is they all test eye movements that originate in the cerebellum. Abnormalities in these tests suggest a central neurological origin.
Saccadic tracking – Saccades are rapid eye movements made to bring an object of interest into the center of the line of sight. Saccades are tested for accuracy, velocity, and latency.
Smooth pursuit tests, also known as sinusoidal tracking, test the ability of the individual to accurately and smoothly pursue a target. In these tests, a target is rotated back and forth in a sinusoidal pattern. Gain is measured and the eye movements are compared to the movement of the target. It is important to note that saccade movements are eliminated from the calculations of gain.
Optokinetic tracking – when a person is spinning, they rely on the stimulation from the vestibular system and optokinetic nystagmus to allow steady focus on objects as they move in a circular pattern around them. As the person’s vestibular system fatigues with stimulation, the optokinetic system is solely responsible for the stabilization of the visual field. ENG tests the optokinetic tracking of targets by passing a light rapidly in front of a patient from one direction to the other and asking the person to count the lights. This is done first in one direction, then the other. Asymmetries are noted and are signs of central nervous system dysfunction. Various tests have been done that have shown unacceptable false positive results with this test. Persons with abnormalities in the optokinetic portion of the ENG may not need further neurological work-up.
Positional and Positioning Tests – Unlike the previous subset of tests, this portion of the ENG tests for abnormalities in the vestibular system. Positional tests are performed to determine whether the vestibular system responds normally and symmetrically to changes in head position. This is based on the concept that when a person receives an insult to one labyrinth, compensation occurs by constant stimulation. It is natural that the subject will become compensated in the position that he most frequently uses, namely the upright position. When placed in different positions, dizziness and nystagmus may occur as a result of incomplete compensation in that particular position.
Caloric Testing (VNG) - This is the only vestibular test that stimulates one side of the vestibular system at a time. In this test, a person is placed in a 30 degree from prone position to allow the horizontal semicircular canal to be in a vertical orientation. Warm and cold water or air is then flushed into the external auditory canal at 7 degrees above or below body temperature. Varying temperature causes a non-physiologic stimulation of one labyrinth that may evoke vertigo, nystagmus, and occasionally nausea and vomiting. Warm water for example causes the perilymph to rotate towards the ampula, resulting in stimulation of the ipsilateral labyrinth and a drift of the eyes away from the stimulated side. The eyes compensate with a saccade toward the stimulated side. The opposite occurs with cold water stimulation. The mnemonic COWS is used to remember the direction of nystagmus (Cold Opposite Warm Same). Ice water irrigations can be used if milder stimulation does not result in nystagmus. Visual fixation should reduce the strength of caloric responses in the presence of normal CNS function. Failure to suppress nystagmus 50-70% with visual fixation is abnormal.
Rotational Chair Testing –
This is the gold standard for determining bilateral vestibular function.
A rotational chair test is performed by securing the patient to a rotary chair which rotates at various speeds and directions while eye movements are recorded. Sinusoidal harmonic acceleration tests at several frequencies, visual-vestibular interaction tests, VOR suppression tests, and step velocity tests are frequently performed using the rotary chair test. The individual’s results are compared to the manufactures’ norms. Persons with two consecutive frequencies out of range are considered abnormal. Persons with unilateral vestibular lesions will often have spontaneous nystagmus in darkness which can create a bias and asymmetry towards the side of the lesion, but this is not always true. After compensation has occurred, gain tends to normalize, but phase generally remains asymmetric. More useful are the results obtained from this test in bilateral vestibular hypofunction. Persons with bilateral vestibular lesions will often demonstrate reduced gain across all frequencies. This may be the first abnormality in persons with vestibular loss associated with gentamicin use.
Computerized Dynamic Posturography (CDP) - This test (also known as platform posturography) is part of the diagnostic workup of imbalance or dizziness and is used to identify the underlying sensory (vestibular, visual, somatosensory) and motor control impairments. CDP is not considered to be a site-of-lesion test but is used to identify and differentiate the functional impairments associated with the pathology.
During CDP testing, the individual wears a harness and stands in an enclosure with a moveable support surface and visual surround. The person is exposed to movement of the support surface and visual surround, and their postural stability and motor reactions are recorded. The entire test set takes approximately 45 minutes to complete. The information gained from this test can be used to determine if a patient may benefit from vestibular rehabilitation.
The term posturography may be used to describe any test of postural stability or standing balance, but is most often used to describe computerized dynamic posturography. Where as ENG and rotational chair testing are designed to evaluate the horizontal VOR by stimulating the horizontal semicircular canals, posturography evaluates other components of balance. Balance requires cerebellar integration of the information from vestibular, visual and somatosensory organs. Dysfunction of any of the necessary components of balance results in stronger reliance on other peripheral sensors for maintenance of balance. Posturographysystematicallytakes awayone or more sensory components to evaluate which component the person is reliant upon for balance.
Vestibular Evoked Myogenic Potential (VEMP) Testing - The purpose of this test is to determine if the saccule, one portion of the otoliths, as well the inferior vestibular nerve and central connections, are intact and working normally. The saccule, which is the lower of the two otolithic organs, has a slight sound sensitivity and this can be measured.
It should be noted that while there is no cure for bilateral vestibulopathy, there is the opportunity for a person’s brain to accommodate some of the side effects through a life-long rehabilitation program. EVERYBODY accommodates at different levels; therefore it is important to have a good working diagnosis so that your rehabilitation specialist can map out a course that works for you. For some people, graduating to advanced vestibular therapy is helpful. The important thing to remember is DO NOT GIVE UP! Stick to your exercises, and fight to learn your new normal!
What is Vestibular Rehabilitation Therapy (VRT)?
VRT is a form of physical therapy designed to promote compensation and habituation for persons with vestibular and balance disorders. The therapist will begin with a thorough evaluation, including observation of balance, posture, gait, movement, and compensatory strategies. What are the reasons for referral?
Poor balance; History or risk of falls; Persistent vertigo; Blurred vision.
Some rehabilitation procedures performed - Rehabilitation may include habituation head exercises, exercises for positional vertigo, balance retraining, safety training, training in mobility skills, and training in daily life activities.
Visual acuity exercises to assist with oscillopsia.
Some goals of therapy - Improve balance; Minimize falls; Reduce intensity, frequency, and duration of vertigo; Reduce or eliminate related symptoms such as headache, fatigue, muscle tension, nausea, and lightheadedness; Increase independence in activities of daily life; Develop compensatory strategies for managing dizziness, disequilibrium, and anxiety.
Advanced Vestibular Rehabilitation (AVT) - Select AVT programs may also involve a customized home-based exercise option (your treating doctor of audiology will determine if that’s the right option for you).
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