Neil T. Shepard, PhD, CCC-A
Over the years, one of the principal uses of vestibular function evaluations, both direct examination and laboratory studies, has been to differentiate between peripheral and central vestibular system disorders. In most cases well-defined abnormalities on pursuit tracking or with saccade testing are indicators of central vestibular system involvement. However, just as a significant caloric asymmetry would be taken as an indication of peripheral dysfunction, the abnormal central findings on vestibular laboratory testing need to fit with the symptom presentation to suggest that those findings relate to the patient's presenting complaints. It is the purpose of this article to review the signs and symptoms associated with dizziness that would more likely be of central vestibular origin.
The symptoms being reported by the patient can be very useful as a first filter to narrow etiologic possibilities and serve as a framework for interpretation of the findings from the formal laboratory or by means of direct office examinations. To make use of the presenting symptoms, the examining audiologist needs details of the symptoms. Recognize that the most common term used by a patient is that of dizziness. The term dizziness is a general term that can encompass imbalance, lightheadedness, objective vertigo (objects in the room appear to move) and subjective vertigo (the sensation of spinning is within the patient's head, objects in the environment are stationary), or combinations of the above. Therefore, in extracting the history of the presenting and past symptoms there are four areas of information that play a major role in helping to provide a first-pass judgment as to whether the symptoms would be most likely of peripheral or central origin. These four are as follows:
Before looking in more detail at the symptom characteristics, which are more typical for central versus peripheral, a brief discussion of the pathophysiology behind true vertigo will be useful. Vertigo, independent of its anatomical lesion site, results from sudden, asymmetrical neural activity. The asymmetry in neural activity could be anywhere from the labyrinths to the posterior cerebellum with the inclusion of the Pons area of the brainstem. The distinction between labyrinthine involvement and other structures within the posterior fossa would be by the presence of brainstem/cerebellar symptoms of the "Ds." It is highly unlikely that lesions in the midbrain or above will produce true vertigo even with right-left asymmetries in neural activity. For the centers above the posterior fossa, the most common complaints would be lightheadedness and imbalance without any vertigo. This implies that with vertigo as a complaint, especially objective vertigo, the lesion is far more likely to be confined to the posterior central circulation system involving the vertebral arteries, basilar artery, and the Circle of Willis. In contrast, the area of the brain fed primarily by the anterior circulation involving the carotid arteries is much less likely to be involved if the complaint is vertigo.
One can make a broad generalization regarding the symptoms that are more likely to be of peripheral origin compared to those of central origin. Table 1 shows this generalized separation. As shown in Table 1, when a peripheral lesion is involved, onset is more often than not sudden and usually memorable as the patient will be able to tell you a specific date and in some cases a specific time. True vertigo, where a patient reports seeing objects moving in the room, would be the most common initial symptom. If the peripheral condition is provoking paroxysmal, spontaneous events of true vertigo such as that seen in Meniere's syndrome, it would be highly unusual to have the true vertigo last longer than 24 hours continuously. However, a single spontaneous onset of a vestibular crisis event (e.g., vestibular neuronitis or labyrinthitis) can have vertigo that will persist for 24–72 hours on a continuous basis, then resolving into head motion provoked symptoms. Vestibular crisis events do not create paroxysmal, spontaneous symptoms. If the presentation were of head movement provoked symptoms, it would be typical to have the dizziness last for only seconds to 2 minutes after a provocative movement if the patient stops his or her activity. Lastly, it would be much more common to have auditory symptoms accompany a peripheral (labyrinthine or VIIIth nerve) lesion.
In contrast, lesions of central origin are usually slow in development, with the patient unable to give you a time of onset. This can also be true for symptoms from nonvestibular involvement (e.g., peripheral neuropathy). If symptoms are of sudden onset with vertigo or imbalance and they do not involve the labyrinthine or VIIIth nerve, then usually you have accompanying symptoms suggesting posterior fossa involvement ("Ds"). The principal symptom is more likely to be that of imbalance and lightheadedness with vertigo absent. In cases where psychological conditions such as anxiety are a major portion of the disorder, the symptoms may be very vague, with the patient struggling to articulate his or her experiences. The psychological group is also more likely to present with subjective vertigo that is a slow spinning within the head that is present on a constant basis and exacerbated by visual motion and/or complex visual patterns.
It would be very comforting if all patients fell clearly into the group of peripheral or central symptoms; however, this is not the case. While patients will have a dominant group of symptoms that will be more closely tied to peripheral or central origin, there will be those who have a full mix of the two groups. Therefore, the above discussion is provided as an initial guide but it is certainly not the final answer. Just as we have done with symptoms, the signs (either direct office examination or formal vestibular and balance laboratory findings) that are presented, when mixed with the symptoms, begin in most patients to present a clearer picture of the origin of the dizziness. Table 2 presents a generalization of signs divided as was done for symptoms into peripheral and central origin.
As presented in Table 2 the lesion of peripheral origin is likely to present with direction-fixed, dominantly horizontal nystagmus. The nystagmus, especially in the subacute and chronic states may likely only be seen with visual fixation removed and when visualization will be direction fixed, independent of the direction of gaze. These patients will typically follow Alexander's law with increasing intensity of the nystagmus as they gaze in the direction of the beat of their nystagmus. In contrast, the lesion of central origin is more likely to present with pure vertical or torsional nystagmus and if horizontal it is more likely to change direction based on the direction of the patient's gaze. Other contrasting features would be the absence of abnormalities on pursuit tracking and saccade testing in the peripheral lesion and the likelihood of seeing abnormalities on these tests in the patient with a central lesion. Headshake testing in the horizontal or vertical direction, if nystagmus is produced, should be horizontal from either direction of shaking for the peripheral lesion and may well be vertical for the central lesion. Although most persons with sudden onset of severe peripheral origin vertigo with nystagmus say they could not walk at the beginning, they actually are able to coordinate their lower limbs in a walking pattern even though they may well need assistance secondary to the severe imbalance. However, central vestibular lesions may well produce a situation where at the onset of symptoms, if they are sudden, the patient cannot coordinate the lower limbs in a walking pattern and cannot walk even with assistance.
When considering the signs that represent possible central system involvement, abnormalities in pursuit tracking and in random saccade testing are such that they are specific to central system deficits. There are no peripheral lesions that are known to produce abnormalities in either of these two tests, with the exception of the spontaneous nystagmus that can exist from an acute peripheral lesion of any etiology. To further discuss in detail the interpretation of pursuit tracking and that of random saccade testing is beyond the limited scope of this article and the interested reader is referred to the suggested resources listed at the end of the article for further detailed information in this regard. The two other principal indicators of central involvement, the type of nystagmus (pure vertical and pure torsional) and nystagmus provoked by eccentric gaze, require further explanation as these are the most likely to be confused with possible peripheral system involvement.
Is pure vertical down- or upbeating nystagmus to be considered peripheral or central in origin? In answering this question it is useful to consider the specific eye movements that are provoked in a normal individual when each of the semicircular canals is individually stimulated. The movements considered below are the compensatory eye movement (slow component of nystagmus), the vestibulo-ocular reflex (VOR), when the canal in question is stimulated, not the beat or fast component.
Using the above descriptions of the VOR responses for each of the canals, the only way to produce a down-beating nystagmus from the periphery would be with simultaneous stimulation of both anterior canals. The VOR response would be pure up with the torsional components canceling and the beat would be down. To have this happen via a pathological insult would require that both anterior canals have simultaneous irritative lesions or have simultaneous paretic lesions of both posterior and horizontal canals. Currently, there is only one condition that has been reported that is a peripheral disorder known to produce at least transient pure down-beat nystagmus: bilateral superior canal dehiscence. Otherwise, the likelihood of a peripheral disorder capable of causing pure vertical up- or down-beating nystagmus is so remote that pure vertical nystagmus should be considered of central origin until proven otherwise. This same rationale may be applied with the use of the specific individual canal eye signatures to pure torsional and pure up-beating nystagmus.
Of the principal signs for central involvement, gaze stability during eccentric gaze is the only one in which abnormalities of either the peripheral or central vestibular and ocular motor systems can produce abnormalities. Therefore, it is best to lay out distinguishing and contrasting features that will allow for this peripheral versus central nervous system differentiation. The principal abnormality noted in gaze stability testing would be the development of nystagmus in place of steady gaze, referred to as gaze-evoked nystagmus. The general characterizations of gaze-evoked nystagmus of peripheral origin are given in Table 3, and those characterizations associated with gaze-evoked nystagmus of central origin are given in Table 4. While all of the characteristics listed can be observed, the dominant one for determining that the gaze-evoked nystagmus is of peripheral origin is the enhancement in the nystagmus with fixation removed. For gaze-evoked nystagmus of central origin, the dominant characteristic is that of direction-changing nystagmus or pure vertical or pure torsional nystagmus.
Another aspect of gaze-evoked nystagmus of central origin is a feature referred to as rebound nystagmus. In this situation, nystagmus is produced beating in the last direction the eye moved as the eye is returned to primary position from eccentric gaze. Even for a normal individual, if the eccentric gaze is held for an extended period of time, one to two beats of nystagmus may be visualized. What is being tested for is a burst of nystagmus lasting several seconds, with the fast component in the last direction of movement of the eye. For example, if persistent gaze-evoked, right-beating nystagmus is noted on right gaze, then on return to center (a leftward eye movement) a brief event of left-beating nystagmus is seen that does not persist.
A caveat to the above discussion is the realization that the signs and some of the symptoms that we would associate with central nervous system involvement can be produced by migraine headaches. Virtually all of the abnormal findings we have discussed for both central and peripheral lesions, as well as abnormal caloric and rotational chair findings, have been reported in patients where migraine headaches were the principal cause of their dizziness. It is beyond the scope of this article to present a full discussion of migraine-related dizziness and the reader is referred to the suggested resources, but it is worth noting that this can be a factor of confusion.
While a brief discussion, hopefully this article has provided the essentials on the use of presenting symptoms and signs to assist in the identification of dizziness of central origin. Those desiring further details on the above issues are referred to the resources that provide the basis behind the information presented herein and are the suggested readings for continued study in this area.
Dr. Shepard is the director of the Dizziness and Balance Disorders Program at the Mayo Clinic, Rochester, Minnesota, and is a professor of audiology in the Mayo Clinical School of Medicine. He received his undergraduate and master's training in Electrical and Biomedical Engineering from the University of Kentucky and the Massachusetts Institute of Technology. He completed his PhD in auditory electrophysiology and clinical audiology from the University of Iowa in 1979. He has specialized in clinical electrophysiology for both the auditory and vestibular systems. His work over the past 28 years has been focused on clinical assessment and rehabilitation of patients with balance disorders and on clinical research endeavors related to both assessment and rehabilitation. Contact him at Shepard.Neil@mayo.edu.
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Furman, J. M., & Cass, S. P. (2007). Balance disorders: A case-study approach. Philadelphia: F. A. Davis.
Furman, J. M., Marcus D. A., & Balaban, C. D. (2003). Migrainous vertigo: Development of a pathogenetic model and structured diagnostic interview. Current Opinion in Neurology, 16, 5–13.
Jacobson, G. P., & Shepard, N. T. (2008). Balance function assessment and management. San Diego, CA: Plural Publishing.
Leigh, J. R., & Zee, D. S. (2006). The neurology of eye movements (4th ed.). New York: Oxford University Press.
Staab, J. P., & Ruckenstein, M. J. (2007). Expanding the differential diagnosis of chronic dizziness. Archives of Otolaryngology-Head & Neck Surgery, 133, 170–176.
The following websites and related information are provided for the convenience of our readers. ASHA does not endorse specific programs, products, or services.
The American Institute of Balance
8200 Bryan Dairy Road, Suite 340
Largo, FL 33777
727-398-5728 (Phone), 727-398-4914 (Fax)
Atlanta Ear Clinic
Suite 470, 980 Johnson Ferry Road
Atlanta, GA 30342
Chicago Dizziness and Hearing
645 N. Michigan Avenue, Suite 410
Chicago, IL 60611
312-274-0197 (Phone), 312-376-8707 (Fax)
Emory University Rehabilitation Medicine
Division of Physical Therapy
1441 Clifton Road N.E., Suite 170
Atlanta, GA 30322
200 First Street S.W.
Rochester, MN 55905
NeuroCom International, Inc.
9570 SE Lawnfield Road
Clackamas, OR 97015
800-767-6744 (US only)
Vestibular Disorders Association
P.O. Box 13305
Portland, OR 97213-0305
800-837-8428 (Phone), 503-229-7705 (Phone)