Patient History
Before performing any vestibular test, taking a thorough medical history and ascertaining the patient’s symptoms constitute the first steps in caring for a patient with a vestibular disorder. Sometimes the patient history alone may suggest a diagnosis.
Taking a patient history should include determining the patient’s symptoms, including balance, hearing, vision, somatosensation, and motor function. The first task for a neurotologist is to allow the patient to describe what he or she senses. The clinician may help the patient in choosing the correct terms to describe his complaints.
Vertigo can be described as an unreal sense of rotationary movement. It should be distinguished from dizziness, which describes any kind of altered sense of orientation. A history of vertigo is of great value in identifying the presence of vestibular pathology but not in localizing its origin. Vertigo results from impaired tonic symmetry in the inputs of the vestibular nuclei. Therefore, a vestibular lesion can occur anywhere within the vestibular end-organs, the vestibular nuclei, the cerebellum, the pathways connecting these structures in the brainstem, and, rarely, within the cortex.
The differentiation between peripheral and central nervous system (CNS) lesions may be based on detailed features of vertigo, even though these features may not apply to every patient. The clinician should determine whether the vertigo occurs in episodes or continuously. If it is episodic, it should be ascertained how often the episodes occur and how long they last. In peripheral causes, vertigo occurs in episodes with an abrupt onset. It disappears in varying time periods, from seconds to days, based on the underlying pathology. The origin of intensive, episodic vertigo that lasts up to a minute is more likely benign paroxysmal positional vertigo (BPPV) if it is provoked with particular positions. Another cause of brief but recurrent vertigo or dizziness, especially if precipitated by body straining, is perilymph fistula. Vertigo that lasts 2–20 minutes is consistent with a transient ischemic attack, which affects the posterior circulation if it is associated with visual deficits, ataxia, and localized neurologic findings. Meniere disease causes recurrent vertigo attacks that can last between 20 minutes and 24 hours. An isolated attack of vertigo that lasts more than 24 hours is suggestive of vestibular neuronitis. Autonomic symptoms such as nausea, vomiting, and sweating are common presenting symptoms. Generally, the more intense symptoms a patient has, the more likely it is that the vertigo is caused by a peripheral lesion.
Lightheadedness describes the sensation of unsteadiness and falling or the symptoms similar to those preceding syncope, such as blurred vision and faded facial color. It should be distinguished from both vertigo and visual disorientation. Most often, lightheadedness occurs with nonvestibular causes such as cardiac or vasovagal reflex.
Imbalance is described as the inability to maintain the center of gravity. It causes the patient to feel unsteady or as if about to fall. The causes may be sensory or motor.
The physician should also ascertain the presence of other associated symptoms such as hearing loss, tinnitus, and facial weakness. A positive history of precipitating factors (eg, rapid head movement) may lead the clinician to variants of BPPV. However, identifying the factors that induce vertigo may not be helpful in distinguishing peripheral lesions from CNS lesions because vertigo precipitated by rapid head movements may result from either decompensated peripheral vestibular lesions or CNS lesions. The physician should ascertain whether the patient has a history of falling with no loss of consciousness; this symptom may be associated with Meniere syndrome. Determining whether noise is a precipitating factor may be useful in identifying Tullio phenomenon. A history of brief episodes of vertigo induced by Valsalva-like maneuvers, which increase middle ear pressure, may be indicative of a perilymph fistula, Chiari malformation, or dehiscence of the superior semicircular canal (SCC). Figure 46–1 shows downbeating nystagmus induced by hyperventilation in a patient with superior canal dehiscence syndrome.
Figure 46–1.
Downbeating nystagmus in a patient with superior canal dehiscence syndrome as proven by coronal temporal bone CT. Upper trace (H) indicates horizontal eye movement and the bottom trace (V) vertical eye movement. There is no nystagmus in the horizontal record. At the beginning, a nystagmus is not observed in the vertical trace. However, from 22nd second on, it shows a downbeating nystagmus with gradually increasing slow-phase velocity (up to 10°/s) as hyperventilation deepened.
Determining the patient’s drug history and current drug use (prescription or other) is crucial in evaluating dizziness. Vestibulotoxic drug intake may cause bilateral vestibular end-organ damage, which results in oscillopsia.
The clinician should also query patients about psychological factors. The specific site where dizziness occurs should be identified. Panic attacks or agoraphobia may be suspected if lightheadedness occurs in crowded areas or public places.
Patient Evaluation
The physical examination of a patient with a balance disorder should begin with a complete ear, nose, and throat exam. A detailed neurotologic examination should also be performed; it should include an evaluation for nystagmus and oculomotor function, as well as positional tests, postural control tests, and a cranial nerve examination.
Oculomotor function is tested by asking the patient to gaze at the tip of the clinician’s index finger. The clinician should first hold her or his finger 25 cm away from the patient’s eyes and then move it laterally and vertically, which is the tracking function. The clinician should assess whether the patient’s eye movements are conjugate or disconjugate. In testing the horizontal tracking function, anything other than a smooth horizontal eye movement is assumed to be indicative of vestibulocerebellar pathology. During the vertical tracking test, a superimposed horizontal eye movement (ie, a saccadic intrusion) may occur in patients with a central oculomotor lesion. An imbalance in the tonic levels of activity that underlies the otolith-ocular reflexes leads to static ocular torsion, head tilt, and a skew deviation, which is a vertical misalignment of the eyes that is observed upon switching the cover from one eye to the other.
In assessing for the presence of nystagmus, the clinician should be aware of possible changes in findings at the time of either the acute or chronic phase of the vertigo or dizziness.
Spontaneousnystagmus is identified by having the patient wear Frenzel glasses. If nystagmus is found, the direction of its fast phase, frequency, and amplitude are noted. Determining the characteristics of the nystagmus would give the physician an overall indication, before electronystagmographic testing is performed, if there is an obvious asymmetry in the vestibular system. If primary positional nystagmus is purely vertical or purely torsional, a CNS disorder, usually in the vestibulocerebellum, the vestibular nuclei, and their connections within the interstitial nucleus of Cajal in the midbrain, is likely. Figure 46–2 shows downbeating nystagmus in a patient with diffuse cerebellar atrophy. Spontaneous nystagmus that is peripheral in origin is characteristically diminished by visual fixation and increased only when fixation is canceled.
Gaze nystagmus is identified by holding the index finger at off-center positions. Central origin nystagmus may change its direction with different gaze positions. The direction of peripheral origin nystagmus is fixed in all gaze positions. A low-velocity, direction-fixed nystagmus (ie, 1–2°/s) or a direction-changing, gaze-evoked nystagmus, both of which present only in darkness, can occur as a nonspecific finding both in nonsymptomatic individuals and patients with organic peripheral or central vestibular lesions. While gazing at a distant object, the passive rotation of a patient’s head at the frequency of 1 Hz over 20 seconds causes a patient with oscillopsia to make saccadic corrections and to view the object as no longer being stationary.
Head-shaking nystagmus is evaluated in the same way as gaze nystagmus; however, in head-shaking nystagmus, patients either wear Frenzel glasses or close their eyes. The frequency and speed of the patient’s head shaking should be maintained at sufficiently high levels (at least 160°/s) to elicit the nonlinearity of the diseased vestibular labyrinth. The direction of head-shaking nystagmus may be toward either the side with the lesion or the side without it, and it may be monophasic, biphasic, or triphasic. If a head-shaking nystagmus beats toward the side without the lesion in a patient with no spontaneous nystagmus, the presence of a statically compensated peripheral lesion should be considered.
Dynamic nonlinearity in the SCCs can be tested at the bedside by observing the effect of head rotations on eye movements. With this test, the malfunction of individual canals is examined by applying high-acceleration head thrusts, with the eyes beginning about 15° away from the primary position in the orbit and the amplitude of the head movement such that the eyes end near the primary gaze position. The patient is asked to fix his or her gaze on the examiner’s nose. Any corrective saccade shortly after the end of the thrusts is a sign of an inappropriate and compensatory slow-phase eye movement. Each canal can be tested in its plane.
The presence of a fistula is suspected if nystagmus occurs or if the patient perceives movement of a visual target that is fixed after applying positive pressure to the outer ear canal. A positive test result (ie, Hennebert sign) suggests either a perilymph fistula or Meniere disease. Tullio phenomenon occurs in the same clinical entities when a loud noise is applied. Hyperventilation may induce symptoms in patients with anxiety and phobic disorders, but it seldom produces nystagmus.
Positional tests can be described as either dynamic or static. Static positional tests are discussed in the Electronystagmography section of this chapter.
The dynamic positional test is called the Dix-Hall-pike maneuver. This test is performed to elicit typical nystagmus of BPPV of the vertical SCCs. The patient may be asked to wear Frenzel glasses. In the test, the patient sits on the examination table with his head rotated 45° from the sagittal plane to one side. The patient is then moved quickly into a position where his head hangs over the edge of the table. After a 20-second waiting period, if nystagmus is not observed, the patient is returned to his initial sitting position. The patient then rotates his head 45° from the sagittal plane to the alternate side. Then he is again brought quickly into a position where his head hangs over the edge of the table. Nystagmus is again sought. If rotational or torsional nystagmus is observed in any of the head-hanging positions, then typical nystagmus reversal is expected when the patient returns to the initial sitting position. The horizontal variant of BPPV is investigated in a different way; the patient is placed in the supine position with head raised 30° by the clinician. Horizontal geotropic or ageotropic nystagmus is identified when the clinician rotates the patient’s head to both sides with nystagmus observation time interval. The side of the lesion is determined based on the intensity of horizontal nystagmus produced by head movement toward each side. It is the side of lesion to which head movement creates more intense nystagmus.
Visual acuity is the patient’s ability to read an eye chart while his or her head is moving. The head is rotated passively at a frequency of 1–2 Hz/s. A drop in acuity of two lines or more from the baseline suggests an abnormal vestibuloocular reflex gain.
The examination of postural control includes the following tests: (1) the Romberg test, (2) the pastpointing test, (3) the tandem gait test, and (4) the Fukuda stepping test. Postural control tests are considered to have mild sensitivity and specificity in identifying lesions. Depending on the nature and phase of the pathology, the side of the lesion cannot reliably be identified from these tests. Excessive swaying toward one side in the Romberg test, deviation to one side in the pastpointing test, or rotation to one side in the Fukuda stepping test may all indicate either a paretic lesion of the labyrinth in that side or an irritative lesion in the opposite side. The patient may show sway, rotation, or deviation toward the unaffected side if the peripheral lesion is at the compensated phase.
During the Romberg test, which is used to identify vestibular impairment, the patient is asked to stand still with eyes closed and feet together. An increased sway or fall toward either side is considered abnormal. The Romberg test can be made more sensitive by asking the patient to stand with the feet in a heel-to-toe position and with arms folded against the chest.
The patient and clinician both stand facing each other; they then stretch their arms forward with index fingers extended and in contact with one another. The patient is asked to raise his arms up and bring his index fingers again into contact with the clinician’s index fingers, which are fixed. The patient performs this movement 2–3 times with eyes open; later, the patient repeats the same maneuver with eyes closed. Deviation to one side is considered abnormal.
The patient is asked to take tandem steps with eyes closed. Healthy individuals can take at least 10 steps without deviation. Patients with vestibular disorders fail this test.
The patient is asked to march in place with eyes closed. After 50 steps, a rotation >30° toward one side is considered abnormal.
An evaluation of cranial nerve function may reveal hypoesthesia of the outer ear canal and an absent corneal reflex, as found in acoustic neuromas. Facial nerve paralysis may be associated with herpes zoster oticus. Eye muscle restrictions may be elicited by evaluating the functioning of cranial nerves III (oculomotor nerve), IV (trochlear nerve), and VI (abducens nerve) before the electronystagmogram.
Electronystagmography
Electronystagmography (ENG) is the fundamental test and the first step in a vestibular testing battery to evaluate the vestibuloocular reflex in patients with a balance disorder. It is based on recording and measuring eye movements or eye positions in response to visual or vestibular stimuli.
Standard ENG equipment consists of the following components: (1) an amplifier for amplification of the corneal-retinal potential that occurs following eye movement, (2) band-pass and notch filters, (3) a signal recorder, (4) a light array, and (5) water and air caloric stimulators. The techniques available to record eye movements are electrooculography (EOG), infrared recording, magnetic search coil, and video-recording systems.
An ENG analysis consists mainly of three tests: (1) oculomotor tests, (2) positional tests, and (3) caloric tests. Before each test, the system needs to be calibrated to maintain accuracy. The calibration is performed via a saccade test that is discussed in the section on oculomotor tests.
ENG is very useful in diagnosing vestibular pathology. No other test provides information on the site of the lesion. The data obtained from an ENG test battery support the diagnoses of horizontal BPPV, vestibular neuronitis, Meniere disease, labyrinthitis, and ototoxicity. With acoustic neuromas, it may be helpful to predict the nerve from which the tumor originates; caloric weakness may be associated with a tumor that originates from the superior vestibular nerve. ENG may also predict whether the patient will experience vertigo after acoustic tumor removal. However, relying on ENG alone to identify lesions in the CNS would not be appropriate.
Abnormal findings in ENG testing do not necessarily indicate a definite CNS lesion. One study investigated the ratio of patients with abnormal results as reported by magnetic resonance imaging (MRI) to patients with abnormal ENG findings in different age groups and found a better correlation between MRI and ENG findings in a group of elderly patients. Overall, MRI confirmed a central lesion in 52% of patients with abnormal ENG findings. In contrast, ENG findings were abnormal in 15 of 21 patients (71%) with an abnormal MRI. In two recent studies, only 30–37% of the patients with abnormal ENG findings had abnormal MRI scans.
Oculomotor tests measure the accuracy, latency, and velocity of eye movements for a given stimulus. The standard oculomotor test battery includes saccade tests, smooth pursuit tests, optokinetic nystagmus testing, gaze tests, and fixation suppression testing. All oculomotor tests are performed with the patient seated upright, with the head stabilized. For oculomotor tests, the ENG device should have a light array on which LED (light-emitting diodes) are given as a stimulus. The light array may be rotated vertically for calibration purposes as well as for testing vertical saccades. The center of the light arrays should be at the same level as the patient’s eyes.
Saccades are rapid eye movements that bring objects in the periphery of the visual field onto the fovea. The latency of saccades is very brief. Because peak velocity can be as high as 700°/s, vision is not clear during saccadic movement. Saccades are controlled by the occipitoparietal cortex, the frontal lobe, the basal ganglia, the superior colliculus, the cerebellum, and the brainstem.
To test saccadic eye movement, the patient is asked to follow the LED with as much accuracy as possible. The LED flashes sequentially in two positions: at the center of the array and then 15–20° to the right or left from the center. The interval between flashes is usually a few seconds. The test is repeated vertically.
Three parameters are of clinical significance in evaluating saccades: latency, peak eye velocity, and accuracy of the saccades.
Latency is the time difference between the presentation of a target and the beginning of a saccade. The mean latency is 192 ± 32 ms in normal subjects. Abnormalities in latency include prolonged latency, shortened latency, and differences in the latency between the right eye and the left eye. These abnormalities are observed in the presence of neurodegenerative disease.
The peak velocity is the maximum velocity that eyes reach during a saccadic movement. It ranges from 283°/s to 581°/s for 20° of amplitude in normal subjects. Abnormalities in the saccadic velocity are slow saccades, fast saccades, or a difference in the velocity between the right eye and the left eye. Reasons for saccadic slowing include the use of sedative drugs, drowsiness, cerebellar disorders, basal ganglia disorders, and brainstem lesions. Fast saccades can be observed in calibration errors and eye muscle restrictions. The asymmetry of velocity is observed in internuclear ophthalmoplegia, eye muscle restrictions, ocular muscle palsies, and palsy of cranial nerves III and VI (the oculomotor and abducens nerves, respectively).
Accuracy is the final parameter in the evaluation of saccades. Saccadic accuracy is determined by saccadic movement by comparing the patient’s eye position relative to the target position. Figure 46–3 provides a record of normal saccadic movement with accurate square tracing. If the saccadic eye movement goes farther than the target position, it is referred to as a hypermetric saccade (or overshoot dysmetria). If the saccadic movement is shorter than the target position, it is referred to as hypometric saccade (or undershoot dysmetria). Undershooting by 10% of the amplitude of the saccade may be observed in healthy subjects, whereas hypermetric saccades rarely occur in healthy subjects. Inaccurate saccades suggest the presence of a pathologic condition in the cerebellum, brainstem, or basal ganglia.
Smooth pursuit is the term used to describe eye movement that is created when the eyes track moving objects. Similar central pathways to those of saccadic movement produce smooth pursuit movement. The neural pathways serving the “pursuit system” are distributed in the cortical and subcortical areas of the brain. Smooth pursuit function also involves the fovea.
In a commonly used stimulus paradigm of the smooth pursuit test, the LED moves back and forth between two points on a light bar at a constant frequency and velocity. The patient is asked to follow this moving target. The frequency of the test stimulus should be between 0.2 and 0.8 Hz/s. A typical pursuit velocity is between 20°/s and 40°/s. Performance declines with higher velocities and increasing patient age.
The primary parameters for evaluation are gain, phase, and trace morphology. Gain is the ratio of peak eye velocity to the target velocity. For a stimulus of 0.5 Hz with a sweeping amplitude of 40°, a gain >0.8 is considered normal. A low gain is suggestive of a CNS disorder. Phase is the difference in time between eye movement and target movement. Under optimal conditions, healthy subjects can track a target with a phase angle of 0°. The level of attention and drugs affecting the CNS can destroy pursuit performance.
A morphologic assessment of the trace is also important. Figure 46–4 shows a record of normal tracking eye movement. A morphologic abnormality is referred to as a staircase of saccades, in which the trace shows staircase-like eye movement while the target is followed. Pursuit traces can be impaired symmetrically or asymmetrically. An asymmetrically impaired pursuit is more suggestive of a CNS lesion than is a symmetrically impaired pursuit. Acute peripheral vestibular lesions can also impair smooth pursuit contralateral to the affected side when the eyes are moving against the slow phase of a spontaneous nystagmus.
