Introduction
The term “dizziness” can be used to refer to vertigo, lightheadedness, disorientation, presyncope, confusion, generalized weakness, or postural instability. Given this multiplicity of definitions, the differential diagnosis of dizziness is correspondingly broad. A deliberate and careful clinical assessment of the symptoms and signs associated with a chief complaint of dizziness is an effective strategy in the production of a successful diagnostic approach.
Anatomically, the vestibular system has peripheral and central parts. Critical for normal posture and gait, the vestibular system also supports clear vision during head movements, due to its contribution to the vestibulo-ocular reflex (VOR). The VOR uses head position and motion information derived from the inner ears to direct eye position and achieve gaze stability.
The peripheral vestibular system consists of the vestibular nerve, plus the inner ear balance organs, namely, the three semicircular canals and two otolith organs called the utricle and the saccule. The inner ear is protected within the petrous temporal bone. The semicircular canals—each side having one horizontal, one anterior, and one posterior canal—occur in pairs, called the right anterior left posterior (RALP) and left anterior right posterior (LARP) canal pairs. The two horizontal semicircular canals detect rotation in horizontal planes. This bilaterality and pairing of canals provides redundancy that enables recovery after vestibular system insults. Such recovery is called vestibular compensation. The central vestibular system is less well defined, including but not limited to the brainstem vestibular nuclei and cerebellum.
Vestibular function is inherently multisensory. The neural pathways from the sensory organs of the inner ear, the visual pathways from the eye to the brain, afferents from the neck muscles, the joints of the spine, and the peripheral sensory organs and nerves of the limbs, together provide the brain with redundant cues about movement, that is, acceleration, velocity, and position relative to various reference frames, including position relative to gravity. The outputs of the vestibular system involve the combined function of the brain, spinal cord, peripheral nerves, muscles, and neuromuscular structures. There is also growing interest in processing of vestibular signals in the brain, for example, the role of the brain in determining the threshold above which motion can be detected by the inner ear. Additionally, spatial memory has been reported to be mediated, in part, by projections between brainstem vestibular nuclei and medial temporal lobe limbic structures, such as the entorhinal cortex. This raises the possibility of two-way causal connections between traditional vestibular disorders and temporal lobe diseases such as Alzheimer disease.
Approach to History Taking
It is good to begin by asking about the patient’s subjective experience. Sometimes, the patient will not be able to describe what “dizziness” means, for it can be difficult to put into words. It is crucial to outline all evident aggravating and alleviating factors. The circumstances in which dizziness is aggravated often represent clues to one or more correct diagnoses. It is often helpful to explicitly ask about how dizziness is modified with, or whether it is induced by, motion or positional change. Peripheral vestibular hypofunction, particularly if bilateral, may cause oscillopsia, that is, instability of images during head motion, for example, while looking out the window of a moving vehicle or while walking. During the interview, begin to develop hypotheses about the differential diagnosis. By the end of the history, and potentially before any formal examination, the clinician should already have a fairly good differential diagnosis. This differential diagnosis can then be weighted by the objective findings of a physical examination.
Approach to the Examination
In taking vital signs, it can be helpful to add an orthostatic vital sign test, in which the patient is asked to stand reasonably motionless for a period of at least 3 minutes. Heart rate and blood pressure are traditionally recorded in this standing position. While the patient is standing motionless, they should be observed for complaints of escalating dizziness or blurred vision, as well as alterations of speech and cognition, and note should be made of any marked degradation of postural stability. It is conventional for abnormal orthostatic vital signs to be defined in terms of a large drop in blood pressure or a marked rise in heart rate after the patient moves to an upright position. One must note, however, that blood pressures in the standing position, though they may not reflect a major change from those in the sitting or supine position, may still be significant if they are low. For example, a standing diastolic blood pressure of 55 is a risk factor for dizziness even if the supine blood pressure is not much higher.
Otoscopy may disclose cerumen, a large quantity of which may help explain hearing loss. Middle ear disease, particularly the infrequent but important finding of a middle ear tumor, may be disclosed. All of the tools of the neurological examination have the potential to be useful in the evaluation of the dizzy patient. The methods of the neurological examination are beyond the scope of this review, but selected signs will be described here.
Some observations about mental status should be noted, including attention, which is critical for normal balance and gait. Abnormalities of visual acuity or visual fields may disturb balance and should be observed. Patients should be asked about double vision. In testing eye alignment, the alternate cover test is performed by covering one eye with something opaque while the other eye fixates on the examiner. The covered eye is then quickly uncovered, and the other eye is covered. In a positive test, an eye moves when it is uncovered, indicating a tendency toward misalignment or phoria. To detect strabismus the cover-uncover test is performed by covering one eye with something opaque and observing the uncovered eye for movement. Next, the covered eye is uncovered. In considering these two tests, the alternate cover test is more sensitive, and the cover-uncover test is more specific for detection of misalignment. Vertical misalignment of the eyes, especially if large, strongly favors a localization to the posterior fossa of the brain, though more subtle hypertropia can be seen with acute inner ear disease, possibly due to involvement of the utricle or its nerve.
Smooth pursuit is tested by asking the patient to follow a visual target, such as the examiner’s finger that is slowly moving from right to left and then up and down. The examiner observes the breakdown of smooth pursuit into saccades. The evenness of smooth pursuit depends on frequency and/or the speed of target motion. If the patient is able to follow the examiner’s finger from the midline all the way to the right, then all the way to the left, then back to the midline in less than 3 seconds without saccades, then smooth pursuit is likely normal. The prevalence of saccadic pursuit in older people is high, rendering bedside smooth pursuit less useful with increasing patient age.
During smooth pursuit testing, spontaneous and gaze nystagmus can be recorded. Nystagmus consists of involuntary oscillating eye movements; and the most common type of nystagmus, that is, jerk nystagmus, has well-defined slow and fast phases. In practice, nystagmus is most often coarser with eye deviation and gaze holding in the direction of fast phases. Gaze-holding, direction-switching nystagmus, for example, fast phases to the right with gaze to right and fast phases to the left with gaze to left, is a central sign. Gaze-holding downbeat nystagmus is another central sign that suggests a disturbance of the cerebellum or craniocervical junction. In cerebellar disorders, one may observe positional nystagmus that persists as long as the patient remains in one position, that is, static positional nystagmus.
The clinical head impulse test, which is now commonly performed in emergency rooms, is intended to test the horizontal angular VOR. In this test, the patient is first asked to fixate, for example, on the examiner’s nose or eyes. The patient’s head is then gently turned back and forth about 10–20 degrees to the right or left of midline; then, in an unpredictable fashion, the examiner suddenly turns the patient’s head from an eccentric position to the midline, or past the midline, through a total angle of about 20 degrees, using reasonable caution to avoid injury. In an abnormal result, when the head is suddenly, impulsively turned toward a damaged peripheral vestibular system, the eyes move with the head and then make a corrective saccade away toward the intended direction of fixation.
A dynamic visual acuity test can be performed at the bedside. The patient is asked to view the near vision card while the examiner passively oscillates the patient’s head in the yaw/axial plane at about 2 Hz. If near vision worsens from baseline by more than two lines of vision, the test is abnormal. This usually indicates bilateral vestibular hypofunction. Many patients with unilateral vestibular hypofunction readily report that dynamic visual acuity is less good during the half cycles when the head is being turned toward the affected side, for example, toward the left in a patient who has recently had acute left vestibular neuritis. The Dix-Hallpike positional test is discussed in the next section. Limb coordination can be tested by past pointing tests in which a patient with eyes closed extends both arms and repeatedly touches the examiner’s fingers from above or below. The Romberg sign indicates excessive dependence of balance upon vision and can be caused by a variety of lesions. One cause of a Romberg sign is myelopathy. The walking Romberg test is sensitive to compressive cervical myelopathy and is performed by asking the patient to walk with eyes closed, noting any significant unsteadiness. In the Fukuda stepping test, the patient marches in place with the arms stretched out in front for about 1 minute or 50 steps; turning toward the right or left by more than 20 degrees is abnormal. This test is most useful when strong turning is noted in a particular direction on multiple trials. Gait dysfunction associated with central nervous system lesions frequently features excessively variable step length. In contrast, peripheral nerve lesions in the limbs, such as entrapment neuropathy, may cause abnormalities that repeat, machine like, from one gait cycle to the next. Patients who are able should be asked to walk up and down a hallway so that arm swing, axial stability, foot dorsiflexion, step width, step length, gait velocity, and other features of gait can be assessed and recorded.
Due to the reliance of normal balance and gait function on cognition, particularly attention, one can often bring out deficits through using dual-task paradigms that are intended to introduce a cognitive load during gait tests. For example, a patient can be asked to count backwards while walking, and if the gait velocity declines by more than 20% with the cognitive load, that would be suggestive of a gait disorder associated with limited cognitive reserve and the possibility of a brain disorder.
Benign Paroxysmal Positional Vertigo
Benign paroxysmal positional vertigo (BPPV) is a disorder in which freely floating debris is trapped within and thus disturbs the function of one or more semicircular canals. The utricular macula is invested with calcium- and protein-containing complexes called otoliths. Otoliths can break down, releasing otolith debris that can migrate into the semicircular canals, most commonly the posterior semicircular canal. Head position changes, such as when the patient with BPPV lies down, rolls in bed, or looks up, may place the freely floating debris in a position from which it can move under the influence of gravity, leading to semicircular canal dysfunction and dizziness. A typical patient reports waves of vertigo with changes in position and may, in addition, have other, milder forms of dizziness, such as nondescript dizziness or imbalance while upright. Patients with BPPV are typically able to describe a latency between the position change and the onset of dizziness and may, for example, say something like “I lie down, and then after a second, I feel a big wave of dizziness.”
A diagnosis of BPPV can be made at the bedside with the Dix-Hallpike test. While the patient is sitting, the head is turned 45 degrees toward the right or left. The patient is then laid back supine with the neck extended back 20 degrees. One observes the eyes for 30 seconds, looking for a burst of paroxysmal nystagmus. Depending on the examination environment and the patient’s neck range of motion, it may be appropriate to achieve neck extension by placing a pillow under the upper back. Some patients with severe nausea may benefit from pretreatment with a vestibular suppressant, such as meclizine, before the Dix-Hallpike test is performed. Of note, immediate repetition of the Dix-Hallpike test may lead to a reduction in the intensity of the paroxysmal nystagmus, that is, the nystagmus may be fatigable. This raises some concern about whether the fatigable nature of the nystagmus might cause one to miss the diagnosis. Therefore, if the history strongly suggests BPPV but the Dix-Hallpike test is negative, one should examine again, allowing a longer time in each position, or consider reexamining on a different day.
In the most common form of BPPV, that is, posterior semicircular canal BPPV, the Dix-Hallpike test induces a burst of upbeat and torsional nystagmus. The torsional component is such that the upper poles of the eyes beat toward, that is, have fast phases directed toward, the ground. In the horizontal canal variant of BPPV, the nystagmus is mostly horizontal. In the anterior canal variant of BPPV, there is paroxysmal downbeat nystagmus.
For patients with pure vertical nystagmus, whether paroxysmal or not, the differential diagnosis of posterior fossa brain disease should be considered. Typically, positional nystagmus due to central nervous system disease is nonparoxysmal, in which case the term “static positional nystagmus” is used. Follow-up of patients with downbeat nystagmus of any type is critical to ensure correct diagnosis, and neuroimaging may be indicated.
The Epley maneuver ( Fig. 25.1 ) is highly effective for the treatment of posterior canal BPPV. The goal should be stable resolution of all symptoms rather than incremental or incomplete improvement. In some cases, a prolonged course of physical therapy or multiple in-office particle repositioning maneuvers are necessary for symptom resolution. Adding mastoid vibration to the Epley maneuver remains unproven but anecdotally may occasionally be a reasonable adjunct to consider for refractory cases in which the latency of the nystagmus is long.
In the horizontal canal variant of BPPV, the nystagmus is often seen in the Dix-Hallpike test, however, it is best elicited by having the patient lie supine and turning the patient’s head toward the right or left. The nystagmus of the horizontal canal variant of BPPV is predominantly horizontal. It may be classified as geotropic—that is, beating toward the floor—or apogeotropic, beating away from the floor. The horizontal canal variant of BPPV can be severely symptomatic and refractory. An effective treatment for horizontal canal BPPV is the so-called log roll maneuver ( Fig. 25.2 ). The supine patient is rolled toward one side or the other and continues to roll until they have made a 360-degree rotation around the long axis of the body. With careful instruction, this type of maneuver can often be successfully accomplished by the patient at home in bed. The anterior canal variant of BPPV may respond to a maneuver in which the patient is moved from sitting to supine and, in cases in which it is deemed safe, hyperextends the neck while supine, in which position the patient stays for approximately 30 seconds before sitting back up.
After successful treatment of BPPV and resolution of nystagmus, some patients may experience a post-BPPV syndrome that consists of nonspecific dizziness and imbalance. This typically lasts for a period of weeks. The post-BPPV syndrome has been reported to be associated with utricular dysfunction. This is consistent with the fact that some patients with BPPV also manifest a head tilt and the fact that utricle stimulation varies with head tilted toward either side when the patient upright.
Ménière Disease
Ménière disease, also known as Ménière syndrome, is defined by prolonged episodes of vertigo combined with fluctuating, single-sided or asymmetric, low-frequencypredominant sensorineural hearing loss (SNHL). Over time, many patients with Ménière disease develop progressive hearing loss that involves all frequencies of sound tested. The related Pathology term “endolymphatic hydrops” refers to dilation of inner ear spaces that contain endolymph. The overlap between clinical Ménière disease and hydrops is not one-to-one; however, recent magnetic resonance imaging (MRI) studies support the concept that many patients with clinical Ménière disease do indeed have hydrops. Ménière disease and hydrops are most often idiopathic and likely represent final common pathways of multiple different disease processes that cause inner ear dysfunction. Delayed endolymphatic hydrops may occur years after sudden SNHL.
The diagnosis of Ménière disease is typically made after an audiogram that is performed by an audiologist in a soundproof booth. During a pure tone audiogram, the patient is asked to signal when able to hear a series of frequencies of sounds, presented to each ear at gradually increasing volume starting below the perceptible volume, to identify a threshold above which the patient is able to hear. To distinguish between SNHL and conductive hearing loss, the audiologist looks for evidence of an air-bone gap, defined as a significant difference between the air conduction thresholds and bone conduction thresholds. Air conduction thresholds measure how well a person can hear using headphones or earphones that are inserted into the external ear canals. Bone conduction thresholds measure how well a person can hear when sound is conducted through skull bones, and the stimulus is administered by a vibrating device placed over the mastoid bone behind the tested ear. Conductive hearing loss occurs when there is a disturbance in the conduction of sound information from the outside world through the middle ear. Middle ear function is affected by otosclerosis, otitis media, Eustachian tube dysfunction, and sinusitis. SNHL typically arises from a disorder of the cochlea or the cochlear nerve, though one must bear in mind the possibility of a retrocochlear lesion, in particular a cerebellopontine angle mass, as described later in this chapter.
First-line treatment for Ménière disease consists of limiting and smoothing out dietary sodium consumption over the course of each day. Consuming adequate amounts of water may also lead to a reduction in the frequency and severity of vertigo attacks. If dietary interventions fail, many providers prescribe diuretic medications. Although evidence for the effectiveness of diuretics is limited, most specialists who have treated patients with Ménière disease believe that diuretics are beneficial for at least some patients. The primary treatment goal in Ménière disease is to reduce the frequency and severity of vertigo attacks. Other symptoms of Ménière disease are less responsive to current interventions, and it is questionable whether any medical interventions favorably affect hearing, notwithstanding isolated reports that antiviral medication may reduce hearing loss and vertigo, an intriguing finding that unfortunately is not yet supported by randomized controlled trials. It is helpful for the patient with Ménière disease to have at least a small supply of vestibular suppressant medication available to use in case of a vertigo attack. For this purpose, lorazepam and meclizine are sometimes prescribed.
Although supported by only limited published evidence, intratympanic (IT) corticosteroid injection may be effective and offers the possibility of a sustained reduction in symptom frequency and severity potentially without the need for the long-term use of daily medication. Ablative surgery for Ménière disease is a last resort, appropriate for only a small proportion of patients with the disease. Likewise, ablative IT injection of the vestibular ototoxin, gentamicin, is reserved for refractory cases or patients with otolithic crises of Tumarkin. In otolithic crises, patients acutely lose balance and may suddenly fall, raising serious safety concerns. There is also some evidence suggesting that management of seasonal allergies may contribute to the effective management of Ménière disease.
Vestibular Migraine
In addition to meeting diagnostic criteria for migraine, patients with vestibular migraine experience episodes of dizziness, vertigo, or other vestibular symptoms. Migraine is defined primarily by a history of episodic headaches with nausea or photophobia. A close temporal association between vestibular symptoms and other migraine-associated symptoms, such as dizziness that occurs immediately before onset of headache and photophobia, increases the plausibility of a vestibular migraine diagnosis. The diagnosis of vestibular migraine relies on exclusion of other, better explanations. Although vestibular migraine and Ménière disease may both cause vertigo, it is unusual for migraine-related vertigo to last more than 30 minutes, while vertigo due to Ménière disease often lasts for hours. Many patients with Ménière disease also have migraine. Migraineurs frequently experience visual motion hypersensitivity or excessive sensitivity to optic flow, as while walking down a supermarket aisle lined with rows of items. Of note, BPPV often aggravates migraine, including vestibular migraine. This leads to cases in which patients with recent onset of BPPV present with a chief complaint of headache, nausea, photophobia, or spontaneous episodes of dizziness. This is unsurprising, given that vestibular testing, which induces dizziness, has been reported to trigger migraine symptoms.
Most interventions that are used for migraine headache have been anecdotally noted to be effective for patients with vestibular migraine, though there are insufficient data from randomized trials to guide therapy. Some patients with infrequent symptoms of vestibular migraine can be effectively managed by using as-needed vestibular suppressant medications, such as meclizine or promethazine. Benign paroxysmal vertigo (BPV) of childhood presents with episodic nonpositional dizziness. Many patients with BPV of childhood later develop migraine in adulthood. The approach to BPV resembles that used in the treatment of migraine. A fuller discussion of interventions for migraine can be found elsewhere in this book (see Chapter 11 ).
Acute Unilateral Peripheral Vestibulopathy Including Vestibular Neuritis
Acute unilateral peripheral vestibulopathy (AUPV) is associated with viral inflammation of the labyrinth and/or vestibular nerve. When AUPV is purely vestibular, the term “vestibular neuritis” is used, indicating acute unilateral failure of peripheral vestibular function. Analogously, a similar syndrome of acute unilateral failure of peripheral auditory function exists and is called sudden SNHL. When a patient has the acute signs and symptoms of both vestibular neuritis and sudden SNHL, the syndrome is called acute labyrinthitis. In Ramsay Hunt syndrome, inflammation related to varicella-zoster virus (VZV) involves the peripheral vestibular system, the peripheral auditory system, and the facial nerve. Ramsay Hunt syndrome generally presents with unilateral signs, including peripheral facial palsy, SNHL and tinnitus, dizziness, nausea, and blisters seen on the skin of the external ear. The incidence of Ramsay Hunt syndrome is expected to be lower in locations where a VZV vaccine, also known as the chickenpox vaccine, is available.
Vestibular neuritis causes a buildup, over hours, of acute, severe, and unrelenting vertigo; nausea; vomiting; and inability to walk normally. The clinical course may fluctuate considerably during the first few days after onset. The acute signs of AUPV persist for at least a few days. After this acute phase, more subtle signs remain for months. The persistence of the acute signs of AUPV for days allows one to distinguish AUPV from other disorders. The acute signs of AUPV include spontaneous, unidirectional, predominantly horizontal nystagmus with the fast phases of the horizontal component directed away from the involved ear, reflecting slow phases toward the affected ear. Head impulse testing with sudden, passive impulses delivered toward the affected ear induce corrective “catch-up” saccades, away from the affected ear toward the midline. The patient with AUPV who can walk typically falls or veers toward the affected ear.
Within several days, the spontaneous, unidirectional nystagmus of AUPV typically resolves and is replaced by nystagmus that is evident only upon gaze away from and beats away from the affected ear. This is an example of Alexander’s law, which states that nystagmus is generally most evident upon gaze in the direction of the fast phases. Typically, in acute to subacute AUPV, the patient turns toward the affected ear on the Fukuda stepping test.
Comparable to many forms of neurological recovery, vestibular compensation proceeds over a period of months. For patients with AUPV who are recovering, residual dizziness and imbalance are most notable when the patient is tired. After AUPV, patients typically return to most of their activities of daily living within a month. Some experience prolonged, slow, or incomplete recovery, which can be severely frustrating. This type of frustration may be partially averted by counseling patients in advance about the possibility of incomplete recovery.
Recurrences of the full AUPV syndrome are rare. Months or years after recovery from AUPV, it is common for patients to continue to report mild, brief blurring of vision when the head is turned quickly toward the affected side, as when someone calls the patient’s name. This type of mild gaze instability is typically one of the last features of AUPV to resolve and may be permanent. Additionally, some patients with AUPV develop BPPV, during the weeks following onset of the AUPV syndrome.
There is no consensus on the best acute treatment of AUPV. Anecdotally, early oral corticosteroids, such as high-dose prednisone, may accelerate recovery from AUPV but with uncertain long-term benefits. Most specialists consider initiating an oral corticosteroid medication during the first week after onset of AUPV, and multiple approaches to treatment are common in practice. Vestibular suppressant medications, such as meclizine and diazepam, provide temporary comfort. However, these should be stopped as soon as possible, ideally within the first week. Vestibular suppressant medications inhibit vestibular compensation and slow functional recovery. Vestibular physical therapy after AUPV likely speeds functional recovery. It is common practice to initiate vestibular physical therapy as soon as it is practical, and improvement may be expected to be faster once vestibular suppressant medication use has been discontinued.
Focal Cerebral Ischemia
Cerebral ischemia produces multiple forms of dizziness, the nature of which depends on the sites of ischemia. Extracranial carotid artery ischemia, for example, may be oligosymptomatic, presenting with brief, nondescript lightheadedness and limb tingling. Cerebellar ischemia may present with vertigo that is combined with other focal signs or symptoms. The labyrinthine artery is a branch of the anterior inferior cerebellar artery; therefore ischemia of the branches of this artery can cause audiovestibular dysfunction. Venous drainage of the labyrinth includes the petrosal veins, sigmoid vein, and jugular vein, raising the possibility of audiovestibular dysfunction from venous insufficiency. Almost any form of cerebral ischemia may be expected to come with a degree of postural instability albeit subtle in some instances. Differentiating between migraine and transient ischemic attacks can be challenging, especially for patients who experience a first-ever syndrome involving vertigo; in this instance, associated focal neurologic signs and symptoms further the diagnostic process. Transient ischemic attacks and stroke are covered in greater detail elsewhere in this book (see Chapter 5 ).
Global Cerebral Hypoperfusion
Global cerebral hypoperfusion typically presents with lightheadedness that is greatest in upright positions. It may be due to dysautonomia that involves the sympathetic nervous system and limits the effectiveness of venous return from portions of the body below the heart. The set of disorders that may contribute to dysautonomia includes vitamin B12 deficiency, hypothyroidism, diabetes mellitus, Lyme disease, obstructive sleep apnea, diffuse Lewy body disease, and Parkinson disease.
Dysautonomia should be suspected in patients who report lightheadedness upon standing up from a chair, even when lightheadedness is inapparent upon standing in the exam room. Dysautonomia-related dizziness often waxes and wanes, such that the patient has “good days and bad days.” The first-line treatment for many patients with dysautonomia is maintenance of normal intravascular volume. Some medications cause hypotension, so a thorough review of the medication list is indicated.
Anxiety Disorders
Dizziness is often a symptom of anxiety disorders. Complicating this is the fact that vestibular disorders may also present with or be complicated by the symptom of anxiety. Many patients with anxiety also report marked sensitivity to visual motion, for example, motion of patterns within one’s vision. Persistent postural perceptual dizziness (PPPD) is a syndrome associated with anxiety that is defined by dizziness without spinning vertigo, aggravated by self-movement and complex visual environments. The criteria for PPPD include a requirement that the symptoms are not better explained by another disease or disorder. PPPD often presents after another acute vestibular disorder. Also notable is that patients with migraine or an anxiety disorder may be predisposed to development of PPPD. It has been hypothesized that PPPD is related to excessive dependence on visual cues, consistent with the development of PPPD after diagnosis of another vestibular disorder. In the setting of peripheral vestibular disorder, vision provides another potentially more reliable cue pertaining to position and motion, but it is conceivable that excessive reliance on vision as a cue may lead to dizziness. Based on this idea, vestibular physical therapy programs have been designed with an intent to reweight the brain’s reliance on sensory cues and reduce overreliance on visual cues. Approaches to the treatment of anxiety-associated dizziness may include a combination of vestibular physical therapy, cognitive-behavioral therapy, and medication, such as selective serotonin reuptake inhibitors, though, as always, treatment must be careful individualized.
Cervicogenic Dizziness
Multiple forms of dizziness may be related to the neck. One well-defined example is compressive spondylotic cervical myelopathy, which frequently disturbs postural stability and gait. The term “cervicogenic dizziness,” however, is typically reserved for nonmyelopathic dizziness attributed to altered proprioceptive input from the neck, for example, in the setting of facet arthropathy. The upper cervical spine musculoskeletal structures are invested with projections via cervical dorsal roots to the spinal cord and then the brainstem. Although normal subjects do not appear to rely extensively on neck afferents for balance, those with peripheral vestibular hypofunction manifest higher than normal cervico-ocular reflex gain, indicating greater reliance on cervical cues. This is an example of an instance in which the brain appears to take advantage of the multisensory nature of balance and then relies more on input from sensory channels that are more normal or less noisy, in the event that some sensory channels become less reliable. In support of the plausibility of the role of cervical spine inputs in vestibular function, some pain specialists avoid injecting bilateral cervical facet joints due to the acute loss of bilateral vestibular input and the observation that bilateral deafferentation may cause dizziness or disequilibrium. Cervicogenic dizziness is often associated with neck pain or stiffness. Physical therapy, when deemed safe, is reasonable to consider, presuming that the intent is to improve function of the cervical spine.
Middle Ear Disease
Many patients in otoneurology subspecialty clinics report a sensation of fullness in one or both ears, raising the question of whether dizziness may be due to Eustachian tube dysfunction, which is a common cause of ear fullness. Unequal middle ear pressures cause vertigo in scuba divers, and a similar phenomenon may occur with continuous positive airway pressure (CPAP), when used for treatment of obstructive sleep apnea. Otosclerosis is a disease of the bones of the middle ear and causes conductive hearing loss. Less widely appreciated is that otosclerosis is associated with vertigo and vestibular dysfunction. This may be due to toxic metabolites derived from otosclerotic bones that penetrate the inner ear, leading to SNHL and vestibular dysfunction. Moreover, some patients with otosclerosis undergo stapedectomy, which is associated with a risk of dizziness and vestibular dysfunction.
Third Mobile Window Disorders
Given its location within the petrous temporal bone, the labyrinth is substantially isolated from external pressure changes with two notable exceptions: the round and oval windows. A pathologic third mobile window can be created by a superior semicircular canal dehiscence (SSCD), in which there is an absence or thinning of the bone covering the roof of the superior semicircular canal. Sound waves—the energy of which normally flows preferentially through the auditory portions of the labyrinth—instead travel excessively through the vestibular labyrinth. Loud sounds may trigger dizziness, that is, the Tullio phenomenon. Patients with SSCD report hearing the heart beating, eye movement, or other abnormally amplified sound, such as the sounds of feet on the floor. Audiometry reveals abnormally low thresholds for perception of bone-conducted sound, sometimes to such an extent that the patient can hear the sound of a tuning fork placed on an elbow or knee but not through the air at the same distance. Although the diagnosis is confirmed by a specially protocoled computed tomographic (CT) scan of the temporal bones, it is reasonable in some instances to first obtain an audiogram with air and bone stimuli.
Bilateral Vestibular Hypofunction
Patients with bilateral peripheral vestibular hypofunction present with oscillopsia or gait and balance dysfunction. Less commonly, vertigo may occur, presumably due to incremental, asymmetric loss of peripheral vestibular function. The head impulse test is abnormal bilaterally, as is the dynamic visual acuity test, and a Romberg sign may be present. Bilateral vestibular hypofunction is most often idiopathic, but it can be caused by gentamicin, tobramycin, syphilis, Lyme disease, bacterial meningitis, superficial siderosis, or autoimmune diseases. Patients with bilateral vestibular hypofunction are advised to avoid swimming alone because of the risk of underwater disorientation. Physical therapy may be beneficial, presumably in part because it capitalizes on preserved sensory channels.
Vestibular Paroxysmia
Vestibular paroxysmia is a syndrome of sudden bursts of dizziness. These reportedly can be caused by injury or compression of the vestibular nerve, for example, by vascular loops or other focal disease adjacent to the vestibular nerve. The episodes of dizziness in vestibular paroxysmia have a sudden onset, are short lived, and are sometimes accompanied by lateropulsion. Anecdotally, these episodes are occasionally accompanied by paroxysmal auditory symptoms, and oxcarbazepine may be beneficial, though randomized trials of treatment of this condition are lacking.
Other Focal Brain Diseases
A diverse array of focal central and peripheral neurological disorders may cause dizziness or imbalance. Examples of focal or multifocal central disorders include multiple sclerosis and brain tumors. Patients with Parkinson disease and related disorders may develop abnormal gait, falls, or dysautonomia with sympathetic failure that causes dizziness. Epilepsy occasionally causes dizziness but typically involves additional symptoms, for example, dizziness plus memory lapse. The patient with epilepsy is recognized by the presence of recurrent, paroxysmal, stereotyped, unprovoked behaviors or experiences that are referrable to the brain. Seizures and epilepsy are covered in greater detail elsewhere in this book (see Chapter 24 ).
Chiari malformations (types I and II) are readily visualized on brain MRI. Headache is the most common symptom. The eye movement exam may reveal saccadic smooth pursuit, downbeat nystagmus, and optokinetic nystagmus abnormalities.
In normal pressure hydrocephalus (NPH), gait dysfunction is an early sign. Deficits of cognition and bladder dysfunction typically develop later. Diagnostic tests may include a large-volume lumbar puncture or placement of a temporary lumbar drain. An uncommon cerebrospinal fluid–related condition, intracranial hypotension, can present with headache, dizziness, and balance dysfunction that improve in the supine position.
A vestibular schwannoma or other mass in the cerebellopontine angle may cause dizziness, though the most common first objective sign is asymmetric SNHL marked by a significant word recognition deficit. Balance dysfunction is a later sign, as the size of the tumor grows large enough to compress the brain. On examination, the patient has difficulty understanding whispered speech on the involved side. Significant asymmetric SNHL is an indication to rule out a vestibular schwannoma or other retrocochlear lesion, ideally through the performance of a contrast CT or MRI of the internal auditory canals. When an MRI of the internal auditory canals with contrast is impractical, for example, for patients who have a non-MRI compatible pacemaker, brainstem auditory evoked response tests may provide useful information. As an explanation of imbalance, one should also consider the differential diagnosis of peripheral neurological disorders, such as large fiber peripheral neuropathy due to vitamin B12 deficiency, diabetes mellitus, or excessive dietary consumption of vitamin B6.
Head Trauma
Head trauma can cause dizziness, through multiple mechanisms. Persistent alteration of brain function that begins immediately after a head trauma may in some instances warrant a diagnosis of traumatic brain injury (TBI). TBI patients frequently report dizziness. When TBI is mild, the term “concussion” is sometimes used. Subsequent symptoms may thus, in some instances, be viewed as a postconcussion syndrome. Diagnosis of TBI relies on documentation of altered brain function that begins soon after a head trauma. The head trauma can be either a blow to the head or a rapid acceleration. As is the case for most neurological disorders, a diagnosis of TBI requires that the clinician has reasonably excluded other, better explanations of the symptoms and signs. Head trauma may also cause labyrinthine concussion. It is well known that the labyrinth can be damaged in the setting of a temporal bone fracture. Additionally, head trauma in the absence of skull fracture can damage the labyrinth. Dizziness due to TBI is often aggravated by head motion. It may thus be necessary for physical therapists to reduce the intensity of balance-related exercises to improve their tolerability. TBI may also be a substrate for dysautonomia with sympathetic failure and orthostatic lightheadedness.
Mal de Debarquement Syndrome
In mal de debarquement syndrome (MdDS), exposure to an unusual form of motion, such as an ocean cruise, a long road trip, or air travel, is followed by persistent sensations of rocking, frequently with associated gait and balance dysfunction. Symptoms may improve transiently, upon reexposure to the same type of motion that preceded the onset of the disorder. Some patients occasionally feel suddenly pulled in one direction or another while walking or report aggravation of imbalance when walking past large patterns on walls or floors.
It has reported that carefully selected paradigms involving full-field visual stimuli projected onto a curved wall in an otherwise dark or dim environment may have therapeutic efficacy in MdDS. The availability of this type of therapy remains limited to a handful of centers. Some patients with MdDS also have concurrent migraine that requires treatment. Anecdotally, patients with the MdDS may be less likely to experience a recurrence or aggravation of MdDS when they are treated with a benzodiazepine, such as clonazepam, concurrent with exposure to the same type of motion, for example, during air travel.
Bibliography
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