The Dizzy Patient Part 2

Pursuit eye movements and vor cancellation

When the head and eyes track a moving target (pursuit) or when a target is moving at the same velocity as the head (as in reading a topic in a moving vehicle), the VOR is normally suppressed to maintain a stable image: this is VOR cancellation or suppression (VORS). The integrity of VORS can be assessed by asking patients to fix their vision on their outstretched thumbs while horizontally rotating the head and arms together. In normal individuals, the eyes do not move during this maneuver.16 In patients with cerebellar disease,17 however, and occasionally in patients with brain stem disturbances that affect pursuit eye movements, one can observe a jerky movement of the eyes, suggesting that VORS is incomplete. A number of drugs that affect the function of the vestibulocerebellum can produce this abnormality, including antiepileptic agents, sedative-hypnotics, and tricyclic antidepressants.

Table 2 Characteristics of Nystagmus Elicited by Eye and Head Position

	Nystagmus Type (Examination Technique)
Lesion Site	Spontaneous (Patient upright; eyes straight ahead)	Gaze-Evoked (Patient upright; eyes directed right, left, up, then down)	Positional (Patient supine; head turned first left, then right; Dix-Hallpike: head rotated 45° with patient sitting upright, then supine)
Central	Pure vertical or pure torsion Not decreased with fixation	Direction changing—quick phases in direction of gaze	Nystagmus > vertigo Pure vertical
	Pendular or mixed waveform	Unilateral and not present in straight-ahead gaze	Sustained
	Alternating direction
		Downbeating often accentuated in lateral gaze
Peripheral	Mixed horizontal/torsional	Direction fixed; must be present in straight-ahead gaze (may need to	Nystagmus = vertigo
	Direction fixed		Must be in plane of stimulated canal (e.g., upbeat and right torsional in right Dix-Hallpike)
	Jerk waveform	remove fixation)
	Suppressed by fixation	Can be oblique but not purely vertical

Nystagmus

Nystagmus is a very helpful physical finding in both static and dynamic imbalance. Formal analysis of the slow-phase waveform, as with electronystagmography, can often help localize the causative lesion. Jerk nystagmus, or constant-velocity drifts of the eyes with corrective quick phases, is usually caused by an imbalance of vestibular, optokinetic, or pursuit signals. Lesions of the peripheral vestibular apparatus usually cause a mixed horizontal-torsional nystagmus, with slow phases directed toward the side of the lesion and central pursuit mechanisms generally preserved. Vestibular nystagmus is often suppressed during visual fixation and can easily be assessed by performing occlusive ophthalmoscopy: one eye is covered and the smallest-aperture light is directed at the uncovered eye’s optic nerve head (the so-called blind spot), so that no visual stimulus is available to suppress any vestibular nystagmus. Drifts of the optic disk and retinal vessels may appear or increase in velocity if an underlying vestibular imbalance exists. The clinician should note that because the back of the eye is being viewed, an upward drift of the fundus corresponds to a downward drift of the pupil, indicating an upbeat-ing nystagmus.

Nystagmus can also be induced by a change in head position [see Table 2]. Positional nystagmus frequently results from degenerative changes in the labyrinth—most commonly, oto-conia-derived debris that stimulates the posterior SCC (occasionally affecting the horizontal or anterior SCC) by shifting in response to gravity.18 In the typical clinical picture of probable benign labyrinthine disease, nystagmus is provoked by the Dix-Hallpike maneuver19 (also known as the Nylen-Barany maneuver) and is characterized by a latency of up to 30 seconds, with predominant vertical and torsional components parallel to the affected SCC, and a duration of 10 to 60 seconds.20 This nystagmus may transiently reappear with the slow-phase direction reversed when the patient sits up. Repeat testing with the maneuver may induce further episodes of nystagmus, but fatigability is generally observed.

Peripheral positional nystagmus (i.e., from labyrinthine disease) can be distinguished from positional nystagmus originating in the central nervous system. For positional nystagmus to be considered peripheral, it must be consistent with whichever canal is stimulated by the head position in which it is elicited.21 Most often, central nystagmus is purely horizontal, vertical, or torsional; is conjugate; is without latency; is nonfatigable; and lasts longer than 30 seconds. Its particular characteristics usually reflect a specific lesion location or disease process [see Table 1].

Table 3 Clinical Examination Techniques for Dizzy Patients

Technique	Associated Disorder or Finding
Dix-Hallpike, Epley, and Semont maneuvers	BPPV, other benign labyrinthine disease
Ductions and versions	Extraocular muscle palsy, strabismus
Dynamic visual acuity	Bilateral labyrinthine loss
Head shaking	Vestibular asymmetry
Head thrusts (VOR gain)	Unilateral or bilateral labyrinthine loss
Hyperventilation	Compressive cerebellopontine angle lesions
Occlusive ophthalmoscopy	Spontaneous nystagmus
Ocular alignment	Skew deviation
Past-pointing	Vestibulospinal tone imbalance
Pursuit eye movements	Cerebellar dysfunction
Rapid turns during ambulation	VSR dysfunction
Saccades	Brain stem or cerebellar dysfunction
Tragal compression	Perilymphatic fistula
Valsalva maneuvers	SCD syndrome
VOR cancellation	Cerebellar function

BPPV—benign paroxysmal positioning vertigo

SCD—superior canal dehiscence

VOR—vestibulo-ocular reflex

VSR—vestibulospinal reflex

Diagnosis

When patients complain of dizziness, clinicians should ask themselves a series of key questions to ascertain the underlying mechanism, and they must address whether the patient’s abnormality has a vestibular or a general medical basis [see Table 4]. Psychiatric factors should also be considered.

With dizziness that appears to be vestibular in origin, the clinician must consider whether the abnormality lies peripherally— at the level of the SCCs, the otoliths, the entire labyrinth, or cranial nerve VIII—or lies within the CNS. Central vestibular dysfunction is most commonly associated with lesions in the brain stem or cerebellum.

History

In taking the history, the clinician must elicit a clear description of the patient’s condition, including the duration of vertigo and any factors that worsen or ease the vertigo. The words that patients use to describe their symptoms may be significant, because a number of seemingly synonymous terms often relate to distinct physiologic mechanisms [see Table 5 and Clinical Manifestations, below].

Obtaining an accurate account may require persistent, close questioning. For example, a patient may first indicate that the vertigo lasted all day, but further inquiry may reveal that in fact the patient had recurrent episodes throughout the day and that each episode lasted for only 10 to 15 seconds and was brought on by changes in head or body position. The duration of vertiginous episodes often points toward a diagnosis. Episodes lasting only seconds, especially in association with movement of the head, suggest BPPV. Patients who experience vertigo that lasts for minutes may be suffering from vestibular migraine or perhaps vertebrobasilar insufficiency. When vertigo lasts from hours to a day, Meniere disease should be considered. Vertigo lasting for days to weeks raises concern about vestibular neuritis (acute peripheral vestibulopathy) or labyrinthine infarction.

Clinical manifestations

Vertigo

Vertigo is generally produced when injury occurs to one vestibular apparatus while the other remains intact or when there is asymmetrical involvement. There is a perception of motion, whether of turning, tilting, or rocking, which persists with eyes closed. A classic example is vestibular neuritis, in which inflammation or infection of cranial nerve VIII on the right or left leads to diminished activity on that side relative to the intact side. This imbalance leads to vertigo and nystagmus.

Patients who complain of vertigo should be asked about the direction of perceived movement of the visual world with eyes open and the sensation of rotation with eyes closed. In the case of left vestibular neuritis, nystagmus slow phases will move toward the left, producing the perception of environmental movement to the right when the eyes are open. A head movement to the right would be necessary to produce a leftward slow phase or vestibular ocular reflex; therefore, with left vestibular neuritis, the patient’s perception of self-rotation with the eyes closed will be to the right. Vertiginous patients who fall do so generally in the direction opposite their perceived direction of movement with their eyes closed; therefore, a patient with a lesion on the left side would most often fall to the left. This direction represents a vestibulospinal correction. Unfortunately, many patients are unable to describe the direction of either environmental movement or self-movement during an episode of vertigo because of disturbing vegetative symptoms, disorientation, and altered concentration and attention.

Table 4 Key Questions in the Evaluation of the Dizzy Patient

Is the complaint consistent with an abnormality of the vestibular system?

What level of the vestibular system is involved?

What is the duration of the vestibular disorder?

What factors exacerbate or mitigate the patient’s symptoms?

Is there a strong positional component in precipitating symptoms?

Is there associated tinnitus, hearing loss, fullness, or pressure in the ears?

Are there other neurologic accompaniments?

Are there cerebrovascular risk factors?

Does Valsalva maneuver, coughing, sneezing, laughing, or exposure to loud noise have any effect?

Is there a history of seizures?

Is there a history of migraine, and is headache associated with symptoms?

Is there a family history of similar events?

When vestibular insults are bilateral and of similar severity, patients will generally not experience vertigo. They will, however, manifest other features of vestibulopathy, such as gait imbalance and an abnormal VOR.

Light-headedness

Some patients with complaints of dizziness describe their symptoms as light-headedness. This choice of words raises concern about presyncope. The causes of presyncope (and non-vertiginous dizziness) are manifold and include orthostatic hypotension, cardiac arrhythmia, certain metabolic derangements (e.g., hypoglycemia), use of drugs with anticholinergic activity, and autonomic dysfunction.

Disequilibrium

Disequilibrium most commonly refers to the inability to maintain a normal gait and upright posture—often arising from abnormalities in the proprioceptive pathways, as occurs in peripheral neuropathy, such as from diabetes mellitus or Guillain-Barre syndrome—and disease in the dorsal column medial lem-niscal system in the upper spinal cord and brain stem, such as from cervical myelopathy or vitamin B12 deficiency. Disruption in the descending vestibulospinal tract, as well as cerebellar and other motor abnormalities (e.g., extrapyramidal parkinsonian syndromes or normal-pressure hydrocephalus), may also contribute to the development of disequilibrium.

Table 5 Terms That Patients Use to Describe Dizziness
Bouncing	Rolling
Falling	Spinning
Floating	Swaying
Imbalance	Swimming
Light-headedness	Tilting
Listing	Twisting
Passing out	Unsteadiness
Rocking	Vertigo

Table 6 Etiology of Vertigo
Barotrauma	Phobic postural vertigo
Benign paroxysmal	Psychogenic
positioning vertigo	Seizure
Drugs*	Transient ischemic attacks and stroke
Familial syndrome
Infection/inflammation+	Tumor (e.g., acoustic neuroma)
Meniere disease	Vascular compression
Multiple sclerosis	Vestibular migraine
Otosclerosis	Vestibular neuritis
Perilymphatic fistula

Vegetative Symptoms

Many patients with vertigo experience vegetative symptoms such as diaphoresis, nausea, and vomiting. These symptoms are often related to instability in autonomic centers localized in the floor of the fourth ventricle, in close proximity to the central vestibular apparatus. A chemosensitive trigger zone in this region appears to be involved with a number of autonomic responses. Increased vagal tone may predominate, with pallor and hypotension; however, sympathetic responses (e.g., hyperventilation or fear of falling) may also contribute to autonomic imbalance.

Spatial Disorientation

When exposed to sensory-rich environments, patients with vertigo often experience perceptual abnormalities such as spatial disorientation, confusion, and discomfort. These abnormalities are likely to be related to faulty sensory vestibular processing in the cortical vestibular areas. During vertigo, the patient’s vestibular sensation represents a conflict between labyrinthine sense and self-referred visual senses.

Differential diagnosis

A number of conditions can produce vertigo with characteristic features that often allow the clinician to confirm an etiolog-ic diagnosis [see Table 6].