The "directed" or focused neurological examination for the assessment of cranial nerve VIII includes an evaluation of the external ear, hearing, and vestibular responses. The examination begins with an assessment of gait and balance.
Figure 12-4 (Figure Not Available) Arterial supply of the inner ea(From Schuknecht HF: Pathology of the Ear. Philadelphia, Lea & Febiger, 1993, p 64.)
Gait can often be observed as the patient walks into the examination room. The most useful test to quantify balance is the eyes-closed tandem Romberg's test. Low-normal performance consists of the ability to stand for 6 seconds, heel to toe, with eyes closed. Young adults should be able to perform this test for 30 seconds, but performance declines with age. It is helpful to develop a judgment as to how much ataxia is appropriate for a given degree of vestibular injury. Patients with bilateral vestibular loss are moderately ataxic--they make heavy use of vision and (with a narrow base) are unsteady when their eyes are closed. No patient with bilateral vestibular loss can stand in eyes-closed tandem Romberg's test position for 6 seconds. Patients with an additional superimposed posterior column position sense deficit, as well as patients with cerebellar dysfunction, are unsteady even with their eyes open. Patients with chronic unilateral vestibular loss show very little ataxia, and they can usually perform the eyes-closed tandem Romberg's test. The need to quantify ataxia does not come up in patients with recent unilateral vestibular imbalance, because these patients have a prominent nystagmus. Although numerous vestibulospinal tests have been described over the years, such as the Unterberger and Fukuda stepping test, the test results are not clinically useful because of variable performance in the normal population. In patients with head injury or in those in whom there are other reasons to suspect a central nervous system (CNS) origin of imbalance, basal ganglia function (pulsion/retropulsion tests) should also be performed.
The examination proceeds with an inspection of the external ear and ear canal looking for malformations, infections, masses, or asymmetry. Next, the tympanic membranes should be inspected for wax, perforation, otitis, or mass lesions. It is usually prudent to remove wax before embarking on more sophisticated diagnostic procedures. The tympanic membranes contribute about 20 db to the hearing level. Disorders such as perforation, scarring, fluid accumulation, or wax impaction can cause a conductive hearing loss. A normal tympanic membrane is translucent. Fluid behind the tympanic membrane imparts a straw color.
For bedside hearing assessment, the Rinne's and Weber's tests can be used. In the Weber's test, a vibrating 512-Hz tuning fork is placed on the patient's forehead. If the sound predominates in one ear, the patient may have either a conductive hearing loss in that ear or a contralateral sensorineural hearing loss. In the Rinne's test, the base of a vibrating tuning fork is placed on the mastoid and then placed about an inch away from the ear. Sound is normally appreciated better through air than through bone. If sound is heard better through bone, it is likely that there is a conductive hearing loss. Other tuning fork tests include the Bing's and Schwabach's tests. In the Bing's test, the fork is struck and placed on the mastoid tip. The examiner alternately occludes the patient's ipsilateral external meatus. If the patient has normal hearing or a sensorineural loss, he or she notices a change in intensity with occlusion. If the patient has a conductive hearing loss, he or she notices no change. The Schwabach's test is contingent on the examiner having normal hearing; the patient's hearing is compared with the examiner's. For bone conduction testing, if the patient stops hearing the sound before the
examiner, this finding is consistent with a sensorineural loss. If the patient hears the sound longer than the examiner, it suggests a conductive hearing loss.
In current clinical practice, the wide availability of excellent audiometric testing allows a much briefer screening maneuver to be used with excellent results. The examiner's thumb and second finger are rubbed together at an arm's length from one of the patient's ears. Persons with normal hearing can perceive this sound at this distance. If the sound is not perceptible, this noise is brought closer and closer until it is heard, and the distance is recorded. This simple test identifies high-tone hearing loss, and an unexpected loss or asymmetrical findings may warrant formal audiogram studies or further investigations with the tuning fork maneuvers described earlier.
Spontaneous nystagmus is next assessed using Frenzel's goggles, which are illuminated, magnifying goggles worn by the patient. The goggles are placed on the patient, and over the next 10 to 15 seconds, the eyes are observed for the presence of spontaneous nystagmus. The typical nystagmus produced by inner ear dysfunction is a "jerk" nystagmus--the eyes slowly deviate off center and then there is a rapid jerk, which brings them back to the center position. Most other patterns of nystagmus (e.g., sinusoidal, gaze-evoked) is of central origin. If Frenzel's goggles are not available, clinicians can obtain similar information about nystagmus from the ophthalmoscopic examination, by monitoring the movement of the back of the eye. As the back of the eye moves in the opposite direction to the front of the eye, for horizontal and vertical movements, the examiner must remember to invert the direction of the nystagmus when noting the direction of the fast phase. Furthermore, an attempt should be made to determine the effect of fixation on nystagmus. Nystagmus derived from the inner ear is increased by removal of fixation, whereas nystagmus of central origin is variably affected by fixation. Some types of central nystagmus, such as congenital nystagmus, may increase with fixation. Most forms of central nystagmus, however, decrease with fixation. Frenzel's goggles are an excellent means of removing fixation. In the ophthalmoscope test, fixation can also be removed by covering the opposite eye.
If there is little or no spontaneous nystagmus and if Frenzel's goggles are available, the head-shake test may be performed in an attempt to provoke a nystagmus. In this maneuver, the patient's eyes are closed and the head is moved in the horizontal plane, back and forth, for 20 cycles. A 45-degree excursion of the head to either side, and a 2-cycle/second frequency should be used. Nystagmus lasting 5 seconds or more is indicative of an organic disorder of the ear or CNS and supports further detailed investigation.
All patients with vertigo should receive a Dix-Hallpike positional test ( .Fig 12-5 ). The patient is first positioned on the examination table, so that when lying flat the head will extend over the end of the table. If Frenzel's goggles are available, they are used; however, the test may be adequately performed without them. The patient is moved backward rapidly to lie on the table in the head-hanging-down position. The eyes are observed for the development of nystagmus. If no dizziness or nystagmus is appreciated after 20 seconds, the patient is returned to the sitting
Figure 12-5 Dix-Hallpike Maneuver(From Baloh RW, Halmagyi GH [ed]: Disorders of the Vestibular System. New York, Oxford University Press, 1996, p 331.)
position. The head is then repositioned 45 degrees to the right, and the patient is again brought down to the head-right supine position. After another 20 seconds, the patient is returned to the sitting position, and the procedure is repeated to the left (head-left). A burst of nystagmus, provoked by either the head-right or head-left position, should be sought. The nystagmus of classic BPPV beats upward and also has a rotatory component, such that the top part of the eye beats toward the down ear. The nystagmus typically has a latency of 2 to 5 seconds, lasts 5 to 60 seconds, and is followed by a downbeating nystagmus when the patient is placed upright in sitting position. A lateral-canal variant of BPPV occurs in which the eyes beat horizontally, toward the down ear. Nystagmus that is sustained longer than 1 minute is unlikely to be BPPV.
Although other positional tests can be used, they are of considerably less utility than the Dix-Hallpike test because of the relatively low incidence of causes of positional nystagmus other than BPPV. Central positional nystagmus such as a persistent downbeat or lateral beating nystagmus may be registered best by simple positional maneuvers wherein the head is supine rather than hyperextended, as in the Dix-Hallpike maneuver. Rarely, patients may develop nystagmus related to the position of their head on neck rather than with respect to gravity, and in these instances maneuvers should be done wherein the trunk is rotated with respect to a stable head.
Maneuvers used at the assessment of VOR gain are aimed at documenting bilateral vestibular loss. They need
not be done unless the patient has failed the eyes-closed tandem Romberg's test (see earlier). The dynamic illegible E test is the easiest and most sensitive of these tests. Using an eye chart located at least 10 feet away from the patient, visual acuity is recorded with the head still. Then, the examiner moves the patient's head horizontally at roughly 1 Hz, ±30 degrees, and visual acuity is again recorded. Normal individuals lose zero to two lines of acuity with head movement. Patients with partial to complete loss of vestibular function have a reduction of three to seven lines of acuity. The ophthalmoscope test is done when the dynamic illegible E test result is positive. The examiner focuses on the optic disc and then gently moves the head as described earlier. If the disc moves with the head, it confirms that the VOR gain is abnormal. This test is less sensitive than the illegible E test but is objective in nature. The rapid doll's head test can also be used when the illegible E test result is positive. The examiner stands in front of the patient, and the patient focuses on the examiner's nose. The examiner slowly rotates the patient's head to one side, roughly 30 degrees. Then, while asking the patient to continue to fixate, the head is rapidly rotated to the opposite mirror image position. In a normal subject, the eyes remain fixated on the examiner's nose throughout the entire procedure, moving equal and opposite to the head. In a patient with a poor vestibular-ocular reflex, such as in bilateral vestibular loss, a refixational eye movement is necessary after the head has stopped moving. This test can also sometimes detect unilateral vestibular lesions, because there may be a refixation saccade only when the head is rotated toward the bad side.
The hyperventilation test is most useful in patients with normal examinations up to this point. In this test the patient breathes deeply and forcefully for 30 breaths at a rate of roughly one breath per second. Immediately after hyperventilation, the eyes are inspected for nystagmus with the Frenzel's goggles, and the patient is asked if the procedure reproduced symptoms. A subjectively positive test result without nystagmus suggests the diagnosis of hyperventilation syndrome and is thought to be a sign of an anxiety disorder. Nystagmus induced by hyperventilation can occur in patients with tumors or irritation of the eighth nerve or in the setting of multiple sclerosis.
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