CHAPTER 50

Dizziness, Vertigo, and Ataxia

Henry Cohen, MS, PharmD, FCCM, BCPP, CGP • Darko Todorov, PharmD, BCPS • Michelle Friedman, PharmD, BS • Grace I. Shyh, PharmD, BS

DIZZINESS AND VERTIGO

Vertigo is a precise term, defined as a sensation of spinning or whirling motion; it implies a definite sensation of rotation of subject or of objects about the subject in any plane (Basmajian et al., 2006; Bhattacharyya et al., 2008; Spraycar, 2006). Dizziness is an imprecise term, appropriately and commonly used by patients in an attempt to describe various subjective symptoms such as faintness (analogous to the feelings that precede syncope), giddiness, light-headedness, and unsteadiness; it may include vertigo (Basmajian et al., 2006; Bhattacharyya et al., 2008; Spraycar, 2006). Dizziness is not mental confusion, blurred vision, headache, or tingling. Dizziness is one of the most common complaints causing patients to seek medical attention (Woodwell, 1992). In a United States national survey, dizziness was the 13th most common individual reason to visit a primary care provider (Herr, Zun, & Mathews, 1989). In a study from a general internal medicine outpatient clinic, dizziness was the third most frequent complaint (Kroenke & Mangelsdorff, 1989).

Anatomy, Physiology, and Pathology

Vertigo and dizziness can represent several different overlapping sensations; the pathophysiologic mechanisms are multifactorial. The vestibular nuclei, which are in the medulla and lower pons, receive input from the vestibular labyrinth via the vestibular branch of cranial nerve VIII and from the cerebellum (Herr et al., 1989). Vertigo is an illusion of motion without external stimuli, and it always indicates an imbalance within the vestibular system, although the symptom itself does not indicate where the imbalance originates. Maintenance of the sense of balance depends primarily on input from the vestibular labyrinth, visual system, and proprioceptive nerves arising from tendons, muscles, and joints (Frederick, 1973; Kelly, 1985). Therefore, vertigo and the sensation of dizziness can result from lesions in the inner ear, the deep paravertebral stretch receptors of the neck, the visual–vestibular interaction centers in the brainstem and cerebellum, the thalamus, or the cortex (Baloh & Honrubia, 1990; Frederick, 1973).

Nausea as a result of motion sickness is initiated by stimulation of the labyrinthine mechanism of the inner ear, which sends impulses to the chemoreceptor trigger zone (CTZ), in turn stimulating the vomiting center (VC). The CTZ, located in the area postrema of the fourth ventricle of the brain, is a major chemosensory organ for emesis. The VC is made up of a nucleus of cells located within the medulla. Vomiting is triggered by afferent impulses to the VC. Impulses are received from the sensory centers (e.g., CTZ, gastrointestinal tract) and integrated by the VC, resulting in efferent impulses to the salivation center, respiratory center, and the pharyngeal, gastrointestinal, and abdominal muscles, causing vomiting. The VC may also be directly stimulated by gastrointestinal irritation and vestibular neuritis. Enhanced activity of the central neurotransmitters, including dopamine in the CTZ, and acetylcholine in the VC, are major mediators for the emesis (Baloh & Honrubia, 1990; Frederick, 1973).

History and Physical Examination

Information from the history and physical examination can play a major role in determining the etiology of dizziness. Unfortunately, patients often have difficulty describing precise symptoms of dizziness. Therefore, the provider must take a careful history and perform a meticulous physical and neurologic examination to determine the type of dizziness; this will serve as a guide for confirmatory diagnostic studies (Adams & Victor, 1985; Herr et al., 1989; Lehrer & Poole, 1987). A cardiovascular examination should be done, including supine and standing blood pressure measurements in arms, peripheral pulses, carotid bruits, heart murmur, and heart rate and rhythm. An ear examination is necessary to detect impacted cerumen or infection. Cerebellar function should be tested by performing the finger-to-nose test and having the patient tandem-walk while performing rapid alternating movements. Cranial nerves should be examined carefully by observing for any extraocular movement abnormality or nystagmus.

Dizziness when standing may be the result of vertigo, cerebral hypoperfusion, or disequilibrium (Kroenke et al., 1992). Dizziness when turning, and especially when rolling over in bed, is usually the result of vertigo. If the patient reports having symptoms of dizziness primarily while standing, both supine and standing blood pressure measurements and pulse rates should be determined. The patient should be allowed to be in both the supine and standing positions for at least 5 minutes before the blood pressure and pulse rate are checked. If there is an orthostatic decrease in blood pressure, the symptom is probably the result of impaired central nervous system (CNS) blood perfusion. Unsteadiness while walking, particularly in elderly patients, is often the result of disequilibrium, and its etiology is generally multifactorial. The presence of decreased visual acuity and signs of peripheral neuropathy or abnormal vestibular function support a diagnosis of disequilibrium.

Psychogenic dizziness is a diagnosis of exclusion that should be especially considered in patients with psychiatric disorders, such as major depression, mania, anxiety disorder, and somatization disorders. The diagnosis of a hyperventilation syndrome can be established if symptoms of dizziness are reproduced by having the patient hyperventilate for 2 to 3 minutes.

Once the provider can establish that the patient is describing vertigo, further questioning will aid in determining the specific etiology. The provider must determine if vertigo is a recurrent or monophasic symptom and must assess the duration of the episodes, the circumstances in which vertigo occurs, and the presence of other otologic or neurologic symptoms (Herr et al., 1989; Lehrer & Poole, 1987).

Acute spontaneous vertigo can result from sudden loss of peripheral input caused by damage to the labyrinth or vestibular nerve, or it can be caused by a sudden unilateral impairment of vestibular nuclear or vestibulocerebellar activity (Baloh & Honrubia, 1990; Kelly, 1985). The patient experiences an intense sense of rotation aggravated by head motion and often by lying down, whereas sitting upright and keeping the head motionless relieves the vertigo. The patient usually notices that the visual world is moving slowly in one direction and quickly back in the other direction; this is the result of spontaneous nystagmus. Standing and walking are difficult, and the patient may fall toward the affected side. Acute spontaneous vertigo is almost always accompanied by autonomic symptoms, including malaise, pallor, diaphoresis, nausea, vomiting, and occasionally diarrhea.

The history often provides critical information that will aid in determining whether vertigo is peripheral (labyrinth) or central (brainstem or cerebellum) in origin (Table 50.1; Frederick, 1973; Herr et al., 1989; Lehrer & Poole, 1987). Generally, peripheral vertigo is more severe than central vertigo and is more likely to be associated with autonomic symptoms, ear fullness or pressure, tinnitus, and hearing loss. Central vertigo is typically associated with neurologic symptoms such as diplopia, dysarthria, incoordination, numbness, and weakness. Lesions within the internal auditory canal produce a combination of vertigo, hearing loss, and facial weakness because of the involvement of cranial nerves VII and VIII. A prior history of cardiovascular disease (i.e., hypertension) or stroke may suggest cerebral or brainstem vascular insult—hence, a central etiology. However, a prior history of ear trauma or ear infection accompanied by unilateral hearing loss suggests a peripheral etiology. Patients with central vestibular lesions often cannot stand or even walk a single step without falling.

Patients with peripheral vestibular lesions have impaired balance, but they are able to ambulate, even during the acute phase. Spontaneous nystagmus of peripheral origin does not change direction with gaze in either side, although it increases in amplitude with gaze away from the last phase. In contrast, spontaneous nystagmus of central origin typically changes direction when the patient looks away from the direction of the fast phase. Furthermore, spontaneous nystagmus of peripheral vertigo is inhibited with fixation and, therefore, is usually prominent for only the first 12 to 24 hours. Spontaneous nystagmus of central vertigo often persists for weeks to months.

TABLE 50.1

Features of Peripheral and Central Vertigo

SIGN OR SYMPTOM	PERIPHERAL (LABYRINTH)	CENTRAL (BRAINSTEM OR CEREBELLUM)
Direction of associated nystagmus	Unidirectional; fast phase opposite lesion	Bidirectional or unidirectional
Purely horizontal nystagmus without torsional component	Uncommon	Common
Vertical or purely torsional nystagmus	Never present	May be present
Visual fixation	Inhibits nystagmus and vertigo	No inhibition
Severity of vertigo	Marked	Often mild
Direction of spin	Toward fast phase	Variable
Direction of fall	Toward slow phase	Variable
Duration of symptoms	Finite (minutes, days, weeks) but recurrent	May be chronic
Tinnitus or deafness	Often present	Usually absent
Associated central abnormalities	None	Extremely common
Common causes	Infection (labyrinthitis), Ménière’s, neuronitis, ischemia, trauma, toxin	Vascular, demyelinating neoplasm

MRI of the brain is indicated in patients with vertigo and focal neurologic findings, new onset of severe headaches, or vertical spontaneous or positional nystagmus. In the patient with acute vertigo and profound imbalance, cerebellar infarct or hemorrhage must be ruled out. Any central lesions or hemorrhaging must be identified immediately, because they can culminate in a mass effect with compression of the brainstem. If the indications for an MRI after a physical and neurologic examination are nebulous, the patient should be observed for 24 to 48 hours; on repeat neurologic examination without improvement, an MRI is indicated.

Recurrent attacks of vertigo may occur when there is a sudden temporary and largely reversible impairment of the labyrinth or its central connections (Frederick, 1973; Herr et al., 1989; Lehrer & Poole, 1987). Such attacks typically last minutes to hours rather than days and terminate through restoration of normal neural activity. The duration of vertigo episodes provides additional relevant diagnostic information. Vertigo of vascular origin, such as a transient ischemic attack, typically lasts minutes, whereas those of peripheral inner ear etiology generally persist for hours. On the neurologic examination, if focal neurologic findings are present, imaging studies of the head are warranted. However, patients with vertebrobasilar transient ischemic attacks often have a completely normal neurologic examination between attacks, and MRI of the brain is usually normal.

A screening audiogram and an electronystagmogram are indicated in all patients with recurrent vertigo that is likely to be of peripheral origin (e.g., hearing loss; Frederick, 1973; Herr et al., 1989; Lehrer & Poole, 1987). Vertigo accompanied by hearing loss is common in patients with otosclerosis. Episodes of vertigo with hearing loss, tinnitus, and the sensation of ear fullness occur in patients with Ménière’s disease. Patients with acoustic neuromas usually have hearing loss rather than vertigo. Neurologic symptoms, which are generally referrable to the posterior fossa, include diplopia, facial paresthesia or weakness, and dysarthria, as well as symptoms resulting from dysfunction of the motor and sensory tracts. Patients with vestibular neuronitis, benign paroxysmal positional vertigo, and recurrent vestibulopathy have normal hearing. Patients with benign positional vertigo (BPV) have intermittent episodes of vertigo with head turning. Vestibular neuronitis is characterized by a relatively sudden onset of severe constant vertigo that resolves after days or weeks. Patients with recurrent vestibulopathy have intermittent episodes of constant vertigo lasting for minutes or hours. Vertigo with or without hearing loss in a patient who has recently received aminoglycoside antimicrobials may be the result of an inherent toxic effect on the vestibular labyrinth (Jackson & Arcieri, 1971).

Benign Positional Vertigo

BPV is the most common cause of acute episodes of vertigo. It is characterized by brief (minutes or less) attacks of vertigo and nystagmus with certain head positions, such as lying down or turning over in bed, or tilting the head backward (Baloh, Honrubia, & Jacobson, 1987; Basmajian et al., 2006; Furman & Cass, 1999). The patient can often identify a head position that will trigger symptoms. Symptoms may recur periodically for several days or months. Hearing is not affected. Diagnosis is confirmed by performing the Dix–Hallpike test, during which the patient is moved from the sitting position to a lying position with the head extended 45° backward. This maneuver is repeated with the head extended and turned to the right and to the left. The Dix–Hallpike test usually produces a brief attack of vertigo and nystagmus (Basmajian et al., 2006; Furman & Cass, 1999).

Positional vertigo nearly always is a benign condition. However, in rare cases, it is a symptom of a central lesion (in particular, in the brainstem), from multiple sclerosis, tumors, stroke, or drug intoxication (alcohol and antiepileptic drugs). The Dix–Hallpike test helps distinguish benign positional nystagmus from more ominous central conditions. In BPV, there is a latency period for several seconds before the appearance of a transient vertigo and nystagmus that dissipates on repetition of the Dix–Hallpike test. In BPV, nystagmus lasts less than 30 seconds and is unidirectional (Baloh et al., 1987; Basmajian et al., 2006). Any deviation from this characteristic nystagmus profile should raise suspicion that a central lesion may exist. Central positional nystagmus typically is nonfatiguing and is purely vertical (either up- or downbearing). Most cases of central positional nystagmus have different neurologic findings.

Acute Vestibular Neuronitis

Acute vestibular neuronitis is characterized by a sudden and severe attack of vertigo, often accompanied by nausea, vomiting, and apprehension (Lehrer & Poole, 1987). The symptoms are exacerbated and pronounced on head movements or changes in position. Spontaneous nystagmus occurs with the slow phase toward the abnormal ear. Tinnitus or a sensation of fullness in the ear occurs in about 40% of cases, but hearing remains unimpaired. With the exception of unsteadiness, there are no neurologic signs. Vertigo usually resolves spontaneously over several hours, but it may recur within days or weeks. Acute vestibular neuronitis affects adults of all ages. The cause of acute vestibular neuronitis has not been elucidated, but a viral etiology has been postulated.

Ménière’s Disease

The onset of Ménière’s disease usually occurs in the third or fourth decade of life. It generally presents with a history of antecedent head trauma or otic infection, followed by a constellation of episodes of vertigo, nausea, and ataxia that persist for hours (Ménière’s Guide, 1995; Paparella, 1991). Fullness or pressure in the ear, tinnitus, and fluctuating hearing loss usually precede (but may follow) the episodes of vertigo. There are no associated neurologic symptoms. Examining the patient during an episode of vertigo reveals a typical horizontal-torsional nystagmus of the peripheral type. It is of paramount importance to perform an audiogram in patients with symptoms suggestive of Ménière’s disease because a characteristic, subclinical, low-frequency sensorineural loss may be present (Horner, 1991).

Disequilibrium Without Vertigo

Patients with diminished perception in the lower extremities can experience severe unsteadiness and imbalance when attempting to walk. They often use the term dizziness to describe their disequilibrium; vertigo is not present. These patients are particularly unsteady when walking in the dark because there are few visual cues to compensate for their loss of perception. Disequilibrium without vertigo is often termed multisensory dizziness and occurs when there is partial loss of multiple sensory inputs (e.g., diabetic peripheral neuropathy and retinopathy; Lehrer & Poole, 1987). Loss of proprioception commonly occurs in patients with peripheral neuropathy, vitamin B₁₂ deficiency, tabes dorsalis, and myelopathies.

Drug-induced peripheral neuropathies have been associated with many agents, including phenytoin, phenobarbital, primidone, nitrofurantoin, dapsone, metronidazole, oral contraceptives, colchicine, podophyllin, hydralazine, didanosine, stavudine, zalcitabine, paclitaxel, carboplatin, altretamine, vincristine, vinblastine, and isoniazid (Gallagher, 1994). Toxin-induced peripheral neuropathies have been associated with arsenic, gold, lead, and mercury (Gallagher, 1994). The normal deterioration in gait and balance that occurs with aging can mimic potentially treatable disorders such as occult hydrocephalus, Parkinson’s disease, and the multi-infarct syndrome. An MRI of the brain helps distinguish among these entities.

ATAXIA