Basic Exams, Audiometry and ENG

Chapter four is a discussion of various vestibular testing procedures, describing and comparing some of the associated equipment. Chapter five deals more with test protocols and interpretation of the various test procedures.

4. Basic Exams, Audiometry and ENG
All audiologists have an audiometer. So what can you do with an audiometer that might be of value to the dizzy patient? A comprehensive audiometric evaluation will not allow a firm diagnosis, but history combined with certain audiometric patterns can point you in the right direction.

A patient with a conductive hearing loss and flat tympanogram may be experiencing dysequilibrium as a result of middle ear effusion. In that case, referral to ENT for treatment of the effusion should be done before considering vestibular evaluation.

A patient with complaints of unilateral tinnitus and episodic vertigo may present with a low frequency unilateral sensorineural hearing loss. This pattern suggests the possibility of Meniere’s disease and vestibular evaluation is warranted.

A patient with progressive dysequilibrium (not vertigo), with a high frequency asymmetrical hearing loss, or unilateral decreased speech discrimination should be referred for retrocochlear studies, either ABR or cranial MRI, before considering vestibular testing.

ENG stands for ElectroNystagmoGraphy, which is an electrical graph of nystagmus. These days most people are using video recordings, and the test battery looks at more than just nystagmus. Nonetheless, traditionally ENG refers to the battery of tests used to search for pathological nystagmus associated with gaze and position change, as well as induced nystagmus from caloric testing. Additionally, ENG recording systems are used to evaluate the ocular motor system as a screening for possible neurologic disease.

Lets look at what you can learn from an ENG exam. First, if the patient cannot calibrate properly, consider three possibilities: 1. Poor vision rendering them unable to see the target lights. 2. Cerebellar dysfunction severely impacting their saccadic tracking ability, or 3. Dementia to the point that they don’t understand or can’t concentrate on the task.
If you see any gaze or spontaneous nystagmus, check for the following: 1 Is it affected by visual fixation? (any change in intensity or direction with eyes open versus eye closed?) 2. Is it affected by change in direction of gaze? (does it speed up, slow down, stop or change direction when the patient looks to the right, then the left, etc.?)

You will only see gaze and spontaneous nystagmus occasionally, but you can usually make a pretty clear determination from the nystagmus pattern whether that patient has a peripheral vestibular disorder or not. Remember, if you do have any gaze or spontaneous nystagmus, that can affect all remaining tests in the ENG battery.

The oculomotor battery is a quasi-vestibular test. What you are really doing is performing a screening test of cerebellar dysfunction, which we know deteriorates with age. I think all computerized ENG systems have age matched norms, so you are comparing your patients performance with what is considered normal for their age. Some audiologists try to make a site of lesion diagnosis based on the pattern of oculo-motor abnormalities; I do not. I think we can be helpful to neurologists because our computerized tests can detect subtle abnormalities that might not be detectable to the naked eye of the neurologist. That doesn’t make us neurologists. Any suspicion of significant cerebellar dysfunction should be corroborated by other cerebellar tests such as rapid alternating hand movement, or heel to toe walking.

Most often, oculomotor abnormalities do not signify a specific problem such a brain stem tumor or stroke. Typically, they are a sign of decreased vascular supply to the posterior portion of the brain. As you can see, we are taking a big step away from Audiology when we try to diagnose neurologic disease. You have to keep the test results in context. If you are examining a healthy 50 year old with complaints of positional vertigo; abnormal oculo-motor ability would be a red flag that requires follow-up. The same results on an 80 year old on a few medications is not going to warrant the same attention. Also, asymmetrical oculo-motor abnormality is a huge red flag, and neuro-imaging or referral to neurology is indicated.

Positional testing is primarily used to detect the nystagmus associated with benign positional vertigo (BPPV), but there are other things to pay attention to. First, not all patients with BPPV will be positive at the time of exam. We have found that close to 40% of patients complaining of positional vertigo will not demonstrate vertigo or nystagmus on initial exam. If you incorrectly tell these patients they do not have BPPV based on a negative exam, you have doomed them to additional pointless medical examinations, and denied them effective treatment. If it sounds like BPPV, it probably is BPPV. We will discuss BPPV in detail next week.

It is important to ask the patient if the positional maneuver (Dix-Hallpike) triggered a sensation of vertigo. If they say it did, and there are no nystagmus, consider a non-labyrinthine cause (central or psychiatric).

Caloric testing allows you to look for the presence, strength and symmetry of nystagmus response to temperature change. Caloric testing has been estimated to stimulate the labyrinth comparably to a head movement in the .003 to .005Hz range. This would be analogous to sine wave that takes 200 seconds to complete. For those familiar with an audiogram, caloric testing has been described as analogous to performing a hearing test by presenting 250Hz at 50dB, and making a judgment of normal hearing versus profound hearing loss based on the response to that stimulus only. People with normal hearing will hear that tone, and deaf people will not, but there is a wide range of possibilities between these two extremes. The caloric response looks only at the horizontal canal, and only at the extreme low frequencies. One can not determine that a labyrinth is normal or totally dysfunctional based on caloric testing.
It is important to understand what ENG does not tell you . Please read my article for VEDA regarding common misconceptions regarding ENG testing.

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