Page last modified:
January 10, 2008
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Timothy C. Hain, MD, Chicago Dizziness and Hearing
Page last modified:
January 10, 2008
The purpose of this page is to outline the procedures that we recommend for doing ENG testing. It is not intended to supply much information about interpretation - -this can be found elsewhere.
Also see: Errors in ENG testing
Here we are discussing a collection of procedures typically called "Electronystagmography" or "Videonystagmography". We will use the term "ENG" for both unless otherwise qualified.
ENG's can consist of just a few or many procedures. The "core" procedures are the following:
Other procedures may be used or not depending on the situation and preference of the person doing the testing. They include:
Practically, nearly everything listed here with very few exceptions can be done better at the bedside, but caloric testing requires a machine. So, at one extreme one might just do a caloric, and at the other extreme, 13 different subtests. Generally labs will nearly always do tests for which they can get reimbursed, and are less likely to do tests for which there is no payment through insurance. Thus reimbursement policy essentially determines the thoroughness of patient testing (not a good idea).
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Typical equipment for doing ENG testing. This particular one is sold by ICS. |
We will just make a few comments here. Most ENG testing is presently done using commercial devices sold by a small number of audiology device makers. A list is given here.
They all presently cost somewhere in the neighbohrhood of $30,000. What you get for this is a computer and special purpose software to record eye movements elicited by the procedures above, hardware needed to record eye movements, and devices to present a visual target or squirt water into someones ears. You also get service -- which is very important. Usually things are constantly breaking with these devices that have all these moving parts, and one normally gets to know ones service department people by first name.
In the author's clinical practice, ENG equipment supplied by Micromedical Technologies, Inc. is used, supplemented by an ICS caloric irrigator. There are many other vendors. See this page for more details about ENG vendors.
Practically it is best to go from procedures that are done in the upright postiion, and are unlikely to be very disturbing, to ones that are more stimulating.
The first 4 procedures are done upright, and are commonly called the "oculomotor battery ".
We recommend that one also perform, as a routine, these upright tests --
The next set of procedures are mainly done with the patient supine, and as they can induce vertigo, are best saved for the end. They are sometimes called the "vestibular battery".
Just prior to doing these procedures, if one has an indication, we recommend that one do these "special" tests:
These last ones are low yield procedures, that are generally not paid for by insurance companies, and that we think are best saved for special situations. Bedside testing is generally more sensitive than ENG versions of these tests too.
These are all done upright with the head (chin) stablized against voluntary head movement. Typical devices used for to produce visual stimuli are computer driven projectors, an array of light emitting diodes, and laser spots. The computer projector is the worst of the three, but by far the most convenient. In a dimly lit room, all three work reasonably well.
spontaneous nystagmus test in light and dark
Here patients look at a visual target for at least 10 seconds, and then simply look straight ahead in the dark for at least another 30 seconds. While is very simple, the result of comparing fixation and complete darkness is very valuable and it can diagnose vestibular neuritis as well as a host of more unusual types of nystagmus.
Gaze test and Rebound nystagmus test
Patients look as far as they can to one side for 10 seconds, then return to the center for 10 seconds. Then they look to the other side for 10 seconds, and again return to the center.
calibration test (saccade test)
Patients watch a brightly lit target at least a meter away.
A sequence of spots displaced at roughly 4 second intervals is shown, and the patient asked to follow them. Both horizontal and vertical displacements are usually used, although not interleaved. Random directions and timing is used to make the test unpredictable.
Patients watch a bright spot that moves smoothly across a screen, at a selection of velocities and frequencies. There are several methodologies here -- best of all is a laser galvanometer. However, computer projectors work reasonably well. We are unenthused about LED arrays used to generate this stimulus.
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Vibration test -- a shower massager is used to stimulate the neck over the sternocleidomastoid. Eye movements are recorded using video-frenzel goggles, in the dark. (c) Chicago Dizziness and Hearing, 2007 |
The vibration test is done using simlar methodology to the spontaneous nystagmus test, but entirely in the dark. First one has the patient look straight ahead in the dark. Next one vibrates over the left neck. One then waits another 5 seconds, and switches to the other neck. There are then four segments to the recording - -dark, vibration left, dark, vibration right. This is an emerging test -- very useful !
These procedures can cause trouble because dizzy patients sometimes get dizzier when their inner ear is stimulated. If available, an anti-vomiting drug that doesn't affect ENG testing may be helpful.
Positional testing is generally much more sensitive at the bedside, but it is often done as part of the ENG anyway. The reason why the bedside is more sensitive, is because the clinician can see torsion. The ENG doesn't measure torsion, and usually the tiny little computer generated images shown on the ENG monitor are useless for torsion too.
The goal of positional testing is first to detect positional nystagmus, and if there is positional nystagmus, to determine if it is due to the ear (usually BPPV), brain (central positional nystagmus), or neck (cervical nystagmus).
There are several methods of doing this, but we will only document the methodology that we recommend:
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Dix-Hallpike test. During the ENG, the patient wears goggles. |
The figure above illustrates the Dix-Hallpike test, which is the core positional test. In this test, a person is brought from sitting to a supine position, with the head turned 45 degrees to one side and extended about 20 degrees backward. One records for 30 seconds or until the nystagmus stops, and then returns the person to upright and records for 10 seconds or until the nystagmus stops. Then one repeats the same process in the other direction. A positive Dix-Hallpike tests consists of a burst of nystagmus (jumping of the eyes). The eyes jump upward as well as twist so that the top part of the eye jumps toward the down side.
If there is horizontal nystagmus during the Dix-Hallpike, one should also do the supine roll test as well as the vertebral artery test.
The analysis of positional testing can be very difficult !
Caloric test (see link for more detail)
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Caloric test -- patient is lying on the table while water is being squirted into her ear, and drains into a basin. The goggles on the patient are being used to record her eye movements. (c) Chicago Dizziness and Hearing, 2007 |
The caloric test is the only part of the ENG that one can't do (often better) at the bedside. One should do a very good job on this critical procedure ! It takes a very long time, it is messy, and patients usually are unenthused about them. So, there is temptation to cut corners, but it is a terrible idea !
We recommend doing the test with water (as long as the ear drums are not perforated), and doing at least 4 irrigations, in this order, with the start of each always at least 10 minutes from the previous start.
The reason for this order (others are possible) is so that each irrigation does not "add" to the previous irrigation. If one were to, lets say, follow cold-right with warm left, and perhaps were a bit rushed and didn't wait for 10 minutes, the two irrigations might add. Another problem is that the "reversal" phase of a caloric irrigation might add on to the next one. You avoid both of these problems if you wait 10 minutes.
Conventionally, patients are reclined so that their head is about 30 degrees elevated r.e. the horizontal. Water at either 7 degrees above or below body temperature is flushed into the ear on one side for 30 seconds. Once the irrigation is done, the patient is "tasked" -- given mental jobs to do to keep them distracted. Nystagmus typically builds up and then decays away over about 5 minutes.
If there is no response from one or both ears (i.e. less than 5 deg/sec of nystagmus in total), then one MUST do ice water calorics on that ear to be sure that it/they is not a "dead" ear.
The procedure for "ice" is the following: Obtain ice water, using a large syringe with a blunt tip, irrigate that ear with 25 cc over about a minute. If there is any nystagmus at all, turn the patient over on their stomach so that the head is prone. There is only a "response" if the nystagmus reverses.
The most common reason for "no response" on caloric testing is technical error or laziness - for example using air instead of water, or neglecting to take out the wax before doing the irrigation. Ice water usually gets around this by providing a stronger stimulus. Still, even ice water will not be able to get a caloric out of an ear impacted by wax.
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Analysis step after VNG testing is over. (c) Chicago Dizziness and Hearing, 2007 |
After the testing is done, and patient sent on their way, the person doing the testing normally has to analyze the results. This basically means checking on the computer and correcting as many of it's errors that one can (there are myriads of errors, not all of which can be corrected).
Analysis is best done if one knows what one is looking for. For example, if the patient has positional vertigo, then one looks very hard for BPPV. If the patient is deaf on one side, then one looks carefully for signs of vestibular weakness.
After one analyzes the results, one should summarize your impressions, and print the entire thing out -- yes, all 10 pages or so. Be sure that what you supply to the referral source has enough data that they or at least someone else could "read it" themselves. A purely textual report is worthless, unless you happen to be a well recognized expert on ENG testing.
There are many situations in which one's ENG methodology must be adapted to special patient groups. The links below discuss some of the more common clinical contexts.
Sometimes patient, doctors, nurses or insurance companies ask why one does ENG testing. The purpose of the ENG is to determine whether or not dizziness may be due to inner ear disease.
There are four main parts to the ENG. The calibration test evaluates rapid eye movements. The tracking test evaluates movement of the eyes as they follow a visual target. The positional test measures dizziness associated with positions of the head. The caloric test measures responses to warm and cold water circulated through a small, soft tube in the ear canal.
The ENG test is the gold-standard for diagnosis of ear disorders affecting one ear at a time. For example, the ENG is excellent for diagnosis of vestibular neuritis. The ENG is also useful in diagnosis of BPPV and bilateral vestibular loss, although the rotatory chair test is better at the diagnosis of bilateral vestibular disorders than is the ENG. The calibration and tracking tests are intended to diagnose central nervous system disorders, such as cerebellar degenerations. These tests are generally insensitive compared to an examination by a neurologist or an MRI scan. ENG, however, is much less expensive than an MRI in most institutions.
| © Copyright May 11, 2008 , Timothy C. Hain, M.D. All rights reserved. Last saved on May 11, 2008 |