Vestibular Disorders: Pearls and Pitfalls

Woo Young Choi, MD, PhD, FRCPC; Daniel R. Gold, DO

Disclosures

Semin Neurol. 2019;39(6):761-774. 

In This Article

Making the Diagnosis

Based on the timing and triggers of symptoms, vestibular disorders can be categorized as acute, episodic (triggered or spontaneous), or chronic vestibular syndromes.

Acute Vestibular Syndrome

The acute vestibular syndrome (AVS) consists of rapid onset, continuous vertigo or dizziness lasting for >24 hours, with associated, nausea, vomiting, spontaneous nystagmus, imbalance, and head motion intolerance. Although vestibular migraine (VM) may also be included in this category, particularly if it is the initial attack, this discussion will be limited to the acute vestibular syndrome, which is generally due to either vestibular neuritis (VN) or stroke/transient ischemic attack (TIA). Furthermore, while VM and TIA are episodic conditions, VN and stroke are usually monophasic.

HINTS is a three-step bedside ocular motor examination that has a sensitivity higher than even MR with diffusion-weighted imaging (DWI) to detect an acute stroke in the AVS. This is especially due to the fact that MR-DWI may be falsely negative approximately 20% of the time in the first 24 to 48 hours.[29,30] A "peripheral" HINTS exam should include the following: abnormal (ipsilesional) head impulse test (HIT) AND unidirectional (contralesional) nystagmus AND negative test of skew. For example, right vestibular neuritis causes an abnormal HIT to the right, unidirectional mixed horizontal-torsional left-beating nystagmus (LBN) (that follows Alexander's law, with increased LBN when looking to the left and decreased LBN or no nystagmus in right gaze), and no vertical refixation movement of the eyes with tests of ocular alignment. The HINTS exam should be considered "central" if any of the following are present: normal HIT OR bidirectional or direction-changing gaze-evoked nystagmus OR presence of a skew deviation. Commonly, one or two of the three steps will appear "peripheral," but the presence of even one "central" sign should point the examiner toward a dangerous etiology that requires expeditious neuroimaging.

It can become particularly confusing when patients present with combined peripheral (e.g., abnormal HIT) and central vestibular features (e.g., direction-changing nystagmus). This is often due to (1) anterior inferior cerebellar artery (AICA) territory strokes, causing simultaneous brainstem/cerebellar, and labyrinthine ischemia; or (2) solitary lesions involving the vestibular nucleus, as the peripheral SCC and otolithic afferents become central and converge on the vestibular nuclei. In addition to HINTS, impaired (or asymmetric) smooth pursuit and/or saccade dysmetria can have further localizing value in this situation. Characteristic findings have been described in certain isolated vertigo syndromes affecting the vestibular nucleus (e.g., spontaneous horizontal–torsional nystagmus, abnormal HIT, and ocular tilt reaction), nucleus prepositus hypoglossi (e.g., gaze-evoked nystagmus that is greater ipsilesionally, and ipsilesional spontaneous nystagmus), flocculus (e.g., gaze-evoked nystagmus and abnormal HIT contralesionally, central pattern of head-shaking nystagmus), inferior cerebellar peduncle in the lateral medullary syndrome (e.g., ocular lateropulsion, hypermetric ipsiversive saccades and hypometric contraversive saccades), and nodulus (e.g., periodic alternating nystagmus, central patterns of head-shaking nystagmus).[31–33]

Hearing symptoms, although usually suggestive of a peripheral cause such as labyrinthitis, can be an important clue to a diagnosis of AICA infarction. Acute hearing loss that is ipsilesional to unilateral vestibular loss in the AVS should raise suspicion for labyrinthine ischemia.[34] By evaluating auditory function with finger rub in addition to performing the HINTS examination (so-called HINTS "Plus"),[35] the sensitivity to detect an acute stroke increases (HINTS 96.5% and HINTS "Plus" 99.1%) with only a minimal decrease in specificity (HINTS 84.4%; HINTS "Plus" 83.1%).[34,36] Simply put, so long as they are performed in the appropriate circumstance, the HINTS examination differentiates peripheral (vestibular neuritis) from central (brainstem/cerebellar stroke) causes of the AVS, while the HINTS "Plus" examination adds greater sensitivity to detect acute ischemia also involving the labyrinth.

In addition to the HINTS "Plus" examination, head-shaking nystagmus (HSN) can be helpful in differentiating peripheral versus central causes of the AVS.[22] Following head-shaking, it should be noted if nystagmus was provoked or whether spontaneous nystagmus that was present has changed direction. Ideally, fixation should be removed, which can be carried out by performing occlusive ophthalmoscopy (i.e., viewing one optic nerve while covering the fellow eye) or with Frenzel goggles.[34,37] Central patterns of HSN include vertical nystagmus produced by horizontal head-shaking (known as "perverted" HSN), reversal of nystagmus (e.g., spontaneous right-beating nystagmus at baseline transitioning to left-beating after head-shaking), and vigorous HSN in the absence of unilateral vestibular loss.[38,39]

The etiology of vestibular neuritis is not clear; it may relate to latent herpes simplex virus type 1 in many cases,[40] although use of antiviral medications has not been found to be effective.[41] Corticosteroids may hasten clinical recovery[42] or lead to greater improvement in results of vestibular laboratory testing (e.g., calorics), but there are no clear data to suggest that the final clinical outcome is better in those who receive steroids.[43] Vestibular physical therapy should be recommended to optimize compensation and recovery,[42,44,45] while vestibular suppressants, such as meclizine, should be discontinued after several days so that normal compensation is not delayed. Fortunately, recurrent or sequential vestibular neuritis (resulting in bilateral vestibular loss) is rare[46] (Table 2).

Pearls and Pitfalls: Recent data indicate that about half of patients presenting with dizziness to the emergency department undergo head CT.[47,48] However, head CT has a very low sensitivity (<40%) for ischemic stroke,[49] which is the most common central cause of acute dizziness.[9] For posterior fossa ischemic stroke presenting with dizziness, its sensitivity is estimated to be lower than 10%.[50] Therefore, head CT is not useful to rule out stroke in acute dizziness, and often serves only to falsely reassure the ordering clinician.

As opposed to immediately concluding that a vertiginous elderly patient has a stroke or TIA, or that a vertiginous young patient has a peripheral etiology, the examination in the AVS should guide testing, and age should not be overemphasized.[27] Recent studies suggest that younger patients with dizziness may be at a higher risk of stroke misdiagnosis than older patients.[35,51]

HINTS was specifically evaluated in the context of the acute vestibular syndrome.[29] It is critical for clinicians to understand that HINTS cannot be applied in episodic vestibular syndromes (EVS).[34] For example, in migraine, Meniere's or BPPV, the HIT should be normal, and per the HINTS exam, a negative HIT would then erroneously suggest a central disorder. Of note, the HINTS examination's sensitivity and specificity were based on examinations conducted within 72 hours of symptom onset in patients with continuous symptoms and spontaneous nystagmus in the AVS.[29,34]

A patient with vestibular neuritis may develop compensatory "covert" saccades during the HIT within days to weeks of the injury. As opposed to "overt" refixation saccades that occur shortly after head movements (this is the catch-up saccade that is visible at the bedside), "covert" saccades occur with head movements and cannot be detected at the bedside. This is clinically relevant since a patient with effective covert saccades may appear to have a normal HIT (see example: https://collections.lib.utah.edu/ark:/87278/s6r53kbq). The video head impulse test has the advantage of recording both covert and overt saccades, while also calculating a VOR gain based on the ratio of eye movement velocity (output) to head movement velocity (input; Table 2).

While the HINTS examination is highly effective, its limitations must be understood, particularly the fact that it can only be relied upon to triage and diagnose patients who have AVS. As mentioned above, labyrinthine and brainstem/cerebellar ischemia can occasionally cause an abnormal HIT. Rarely, an unrecognized congenital fourth nerve palsy (or other vertical strabismus) may lead to the false assumption that an acute skew deviation is present. Also, patients with vestibular neuritis can rarely have vertical diplopia due to a small skew deviation (i.e., a "peripheral skew") Box 3.

Episodic Vestibular Syndrome

Triggered Episodic Vestibular Syndrome. Benign Paroxysmal Positional Vertigo: The characteristic history for benign paroxysmal positional vertigo (BPPV) is <1 to 2 minutes of vertigo, which occurs when rolling over in bed, looking up or down, going from the supine to seated position, or the seated to supine position. In PC BPPV, following the DH maneuver, a brief, upbeat-torsional nystagmus (top pole beating toward the lowermost or affected ear) is seen with a latency (a few seconds to occasionally 30 seconds or more) and fatigability on repeated testing.[52] If a patient has horizontal canal (HC) BPPV, horizontal nystagmus is typically observed with DH, although the supine roll test should also be performed. In this maneuver, the patient's head is simply turned 90 degrees to each side. If cervical range of motion is poor, the patient can be rolled 90 degrees to each side. The Epley or Semont repositioning maneuvers have been shown to be highly effective in treating PC-BPPV (http://content.lib.utah.edu/cdm/ref/collection/EHSL-NOVEL/id/2350), while the Gufoni (http://content.lib.utah.edu/cdm/ref/collection/EHSL-NOVEL/id/2351), or BBQ roll (http://content.lib.utah.edu/cdm/ref/collection/EHSL-NOVEL/id/2352) help treat HC-BPPV.[53]

Pearls and Pitfalls: If the history is not typical for BPPV, or anything other than the expected pattern of nystagmus is seen, neuroimaging is warranted to exclude a posterior fossa lesion.[54] Positional downbeat nystagmus is one pattern that may have a central cause, and is normally triggered by DH testing or straight-head hanging (patient is supine and the head is extended 20 to 30 degrees without rotation; Table 1). Another central pattern is apogeotropic positional nystagmus, which is best triggered by supine roll testing (right-beating nystagmus in left roll and left-beating nystagmus in right roll, i.e., beats away from the earth), but is typically seen with DH as well. The distinction between apogeotropic HC BPPV and central apogeotropic nystagmus can be convoluted (particularly since both can persist for minutes; with HC BPPV, this persistence is due to cupulolithiasis), but the following argue for a peripheral (BPPV) localization: predictable change in nystagmus with bow (head flexed forward), lean (head flexed backward), and supine tests; resolution (or change to geotropic nystagmus) with properly performed repositioning maneuvers (e.g., Gufoni); normal ocular motor and general neurologic (including gait evaluation) examination. The following argue for a central (posterior fossa) localization: unexpected nystagmus vector given a particular positional maneuver; persistence despite repeated and properly performed repositioning maneuvers; additional ocular motor or general neurologic exam abnormalities.[55] Another important diagnostic consideration is vestibular migraine, as these patients commonly have positional vertigo and nystagmus, which is usually mild to moderate in nystagmus intensity and symptom severity. This is particularly marked during an acute attack.[56] Commonly, patients with BPPV will have lingering mild dizziness and unsteadiness in between BPPV attacks.

Superior Canal Dehiscence Syndrome: Superior canal dehiscence syndrome (SCDS) is caused by the creation of a third mobile window in the inner ear, in addition to the oval and round windows, as the result of a dehiscence of the superior (anterior) semicircular canal (i.e., thinning or discontinuity of the bone that separates the superior canal from the middle cranial fossa).[26] There are believed to be both congenital and acquired factors which may contribute to the development of SCDS.[57] One large study evaluating the temporal bone in patients with SCDS suggested it is primarily a congenital phenomenon.[58] However, in about one quarter of cases, another inciting injury such as a traumatic head injury or Valsalva is implicated.[59]

Symptoms suggestive of SCDS include Tullio phenomenon (i.e., provocation of vertigo and nystagmus by loud sounds) and Hennebert sign (i.e., vertigo and nystagmus induced by pressure in the external auditory canal).[25,26] With sound or pressure triggers, transient symptoms include unsteadiness, vertigo, oscillopsia (due to nystagmus), or rarely an ocular tilt reaction, in which the head is tilted away from the stimulated side and a skew deviation of the eyes develops with the eye higher on the stimulated side.[26,60,61] Chronic symptoms may include disequilibrium or autophony (perception of internal noises, e.g., hearing one's pulse, eye movements, joints moving/creaking, or one's own footsteps).[62]

The diagnosis of SCDS can be established based on lowered thresholds for eliciting cervical and ocular vestibular evoked myogenic potentials.[63–65] Characteristic audiometric findings include supranormal bone conduction thresholds with an air-bone gap, reflecting an increased excitability of the labyrinth due to a third mobile window.[63] One consequence of supranormal bone conduction is that when a tuning fork is placed on the lateral malleolus, it may be heard in the affected ear (i.e., positive malleolus sign). The definitive diagnosis is based on high-resolution (0.5 mm) CT of the temporal bones, demonstrating an abnormal dehiscence[66] (Table 2).

Many patients can avoid activities that provoke symptoms and do not require surgery. Refractory cases can be treated with surgical resurfacing and plugging of the superior canal.[59] Interestingly, SCDS and migraine often coexist, which likely represents the high prevalence of migraine in the general population and SCDS as an effective migraine trigger.[57] Therefore, adequate control of vestibular migraine is essential to distinguish SCDS from migraine symptoms, so the most appropriate medical or surgical intervention can be selected. Optimal control of vestibular migraine will also minimize the likelihood of a postoperative migraine exacerbation in a patient undergoing SCDS surgery Box 4.[57]

Spontaneous Episodic Vestibular Syndrome. Vestibular Migraine: A diagnosis of vestibular migraine requires the following:[67] (1) at least five episodes with vestibular symptoms of moderate or severe intensity, lasting 5 minutes to 72 hours; (2) current or previous history of migraine according to the International Classification of Headache Disorders (ICHD); and (3) one or more migraine features with at least 50% of the vestibular episodes (≥2 headache features, photophobia/phonophobia, and visual aura). Although the pathophysiology of vestibular migraine is not entirely understood, it is thought to relate to abnormal interactions between the pain and vestibular pathways, as they converge onto brainstem structures (locus coeruleus, dorsal raphe nucleus, and parabrachial nucleus), leading to overactivation of vestibulothalamocortical pathways.[68–72] In addition, peripheral mechanisms may contribute as follows: changes in the trigeminovascular system may cause labyrinthine vasodilation, with plasma extravasation and inflammation mediated by the actions of substance P, neurokinin A, and calcitonin gene-related peptide (CGRP).[70,73–76]

Hour- to day-long attacks of vertigo are most common, but minutes and even seconds of vertigo can occur in vestibular migraine.[68] Distinguishing features for vestibular migraine include concurrent or past history of migraine headache (usually with a family history), or at least migrainous features during vertigo attacks (photo/phonophobia, aura, and menstrual precipitation).[72] Migraine sufferers, especially those with associated vestibular symptoms, are more susceptible to motion sickness.[77–79] The pathophysiology of motion sickness is thought to involve the vestibular nuclei and a variety of neurotransmitters that are also implicated in migraine.[70] Histamine, acetylcholine, and noradrenaline are thought to be involved in motion sickness, and their role is supported by the effectiveness of treatment using antihistamines, scopolamine and amphetamines.[80–82] Serotonin has also been implicated in motion sickness.[70]

Visual vertigo is a condition that may occur subsequent to the development of any vestibular condition, but is quite common in vestibular migraine. Visual vertigo is a specific form of chronic dizziness in which symptoms can be provoked by disorienting, highly patterned visual environments such as crowds, people walking, cars passing by, supermarket aisles, certain geometric patterns, three-dimensional (3D) movies, and large screen televisions.[83,84] Visual vertigo symptoms are thought to be due to an overreliance on visual cues for posture and orientation.[85] Such "visual dependence" is thought to develop from a lack of confidence in vestibular or somatosensory inputs that can occur, for example, in patients with vestibular disorders. Optokinetic exposure therapy may be helpful.[86,87]

There is no specific pattern of audiovestibular test findings in vestibular migraine (Table 2). During attacks of vestibular migraine, spontaneous, headshaking-induced and positional nystagmus are often observed[56] (Table 1). Low-velocity, horizontal positional nystagmus is more common than vertical or torsional nystagmus. The ocular motor and vestibular examination in between attacks is typically normal. After years of vestibular migraine, the examination may show abnormalities such as central positional nystagmus.[88]

Conditions with audiovestibular features and headaches that can mimic vestibular migraine[22] include Susac syndrome, lupus, antiphospholipid antibody syndrome, Sjogren syndrome, MELAS (mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes), CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), episodic ataxia, hemiplegic migraine, spinocerebellar atrophy (SCA) 6, and vertebral artery dissection. Each of these conditions has its own unique examination, laboratory, or radiologic findings that allow for the specific diagnosis to be confirmed. MRI with an internal auditory canal protocol should be considered if the history or examination are not typical for migraine, particularly in patients presenting with a first attack of dizziness or vertigo that may or may not represent migraine.

Treatment of vestibular migraine includes dietary and lifestyle modifications, and/or the use of migraine prophylactic medications. Large-scale randomized controlled trials evaluating abortive (e.g., triptans) and preventive medications are lacking, but anecdotally, most of the preventative agents used for migraine headaches are probably effective for vestibular symptoms as well.

Meniere's Disease: Meniere's disease is characterized by vertigo attacks, lasting 20 minutes to 12 hours, with concurrent hearing loss, tinnitus and aural fullness.[89] Although the exact cause remains unclear, the associated pathology is thought to be endolymphatic hydrops, which is the expansion of the endolymphatic space within the labyrinth.[90–92]

Initially, vestibular or auditory symptoms can occur in isolation but over time the complete set of symptoms almost always develops.[93] Spontaneous nystagmus during attacks can vary, depending on which phase of the attack the patient is in (e.g., ipsilesional during the initial excitatory or irritative phase, or contralesional in the subsequent inhibitory phase). Initially, the hearing loss and tinnitus may resolve completely following an attack. Fluctuating sensorineural hearing loss in the low-mid frequency range, documented by audiography, is characteristic (Table 2). With time, the entire frequency range can progressively become affected in untreated or refractory cases, resulting in severe permanent hearing loss. Meniere's disease becomes bilateral in about half of patients. A drop attack termed Tumarkin's otolithic crisis can occur at all stages of Meniere's disease in which patients feel a sudden, severe pushing to the ground by some external force.[93] This is likely due to an abrupt loss of vestibulospinal reflexes from saccular dysfunction.

The treatment of Meniere's disease mainly consists of sodium restriction and diuretics for mild cases. Intratympanic steroids and gentamicin injection are used in severe refractory cases.[94–96] Symptomatic relief can be achieved, but no treatment has been clearly shown to halt the progressive destruction of the inner ear in Meniere's disease.[97]

Vestibular Paroxysmia: Vestibular paroxysmia is thought to result from microvascular compression of the vestibular nerve, analogous to the well-known pathophysiology of trigeminal neuralgia.[22] The attacks associated with vestibular paroxysmia are short-lived (most often lasting a few seconds to minutes), tend to occur many times each day, and are often provoked by positional changes or exercise. These attacks represent a diagnostic challenge because clinical evaluation during such a short attack is rare and patients are asymptomatic between attacks. Transient symptoms may include vertigo, oscillopsia, tinnitus, aural fullness, or disequilibrium.[98,99] Attacks are thought to be related to ephaptic transmission and may be induced by head movement. Hyperventilation-induced nystagmus is seen in approximately 70% of patients, probably because hyperventilation raises CSF pH and can transiently increase conductivity across a demyelinated segment of CN 8.[99]

A vascular loop that is in contact with CN 8 (usually AICA, vertebral artery, posterior inferior cerebellar artery, or a vein[98]) is best seen on heavily T2-weighted sequences such as constructive interference in steady state (CISS) or fast imaging employing steady-state acquisition (FIESTA) imaging. With high resolution CISS or FIESTA imaging, neurovascular contact in the region of the IAC involving CN 8 and/or CN 7 is often observed as a normal finding, raising the conundrum of whether the contact is causal or coincidental (Table 2). Studies have found that neurovascular contacts between vessels and the eighth cranial nerve can be found in over 20% of healthy asymptomatic individuals.[100] In these instances, the history and examination are most important, and trial of an antiseizure medication like carbamazepine or oxcarbazepine can be both diagnostic and therapeutic.[99] Vestibular testing results consistent with vestibular hypo- or hyperfunction have been described.[98] Abnormal brainstem auditory-evoked potentials may be another marker for this syndrome Box 5.

Chronic Vestibular Syndrome

Persistent Postural Perceptual Dizziness: One of the more common diagnoses made in tertiary balance disorder centers, along with BPPV and vestibular migraine, is persistent postural perceptual dizziness (PPPD).[101] This disorder, previously known as chronic subjective dizziness or phobic postural vertigo, has been described after a vestibular insult (even with a normal vestibular examination and test results), medical illness, or psychological stress.[101–105] The pathophysiology of PPPD is not well known, but it is thought to arise from functional changes in postural control, multi-sensory information processing, and/or cortical integration of spatial orientation.[102,106]

PPPD symptoms are worse when patients are standing or walking, better with sitting, and absent or minimal in the supine position. Its main features include persistent non-vertiginous symptoms lasting 3 or more months, sensitivity to self or environmental motion, and difficulty with precision tasks including reading or computer work.[104] Complex visual stimuli seem to be particularly troublesome. Although mood disorders such as anxiety and depression often coexist with the vestibular symptoms, PPPD does not represent a primary psychiatric condition, but rather a chronic functional vestibular disorder with characteristic behavioral features.[101]

Certain selective serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors have been found to be helpful in treating PPPD along with vestibular physical therapy (mainly desensitization or habituation paradigms). Cognitive-behavioral therapy has shown transient benefits without long-lasting effects.[102]

Bilateral Vestibular Loss: Bilateral vestibular loss (BVL) is a relatively common cause of severe gait imbalance. Generally, unilateral vestibular loss tends to be well compensated, but bilateral loss can be associated with very significant imbalance and visual instability.[22,107] Gait imbalance from BVL tends to be worse in the dark and on uneven surfaces. Oscillopsia that occurs with head motion is almost always present. This type of oscillopsia is particularly noticeable when walking, running, or riding in a car on a bumpy road.

Clinical suspicion of BVL can be confirmed with dynamic visual acuity assessment, quantitative head-impulse test, rotatory chair, and/or caloric testing[108] (Table 2). Loss of four or more lines when assessing dynamic visual acuity (see example of how to perform this maneuver—https://collections.lib.utah.edu/ark:/87278/s6tn19w8) and bilaterally positive head impulses are typical findings on examination.[108] Another suggestive examination finding is instability of the optic nerve during ophthalmoscopy, where the head is oscillated back and forth while the subject is fixating with the fellow eye.

One of the most common causes of BVL is the systemic administration of gentamicin, which is ototoxic, although usually spares auditory function. Gentamicin-induced vestibular toxicity can even occur with only a few days of use.[109] The risk of vestibular toxicity is higher in renal failure and with concurrent use of another ototoxic medication. Other causes of BVL include advanced bilateral Meniere's disease, sequential vestibular neuritis, meningitis, inflammatory or autoimmune disease (e.g., Cogan's syndrome), superficial siderosis (often with anosmia and cerebellar dysfunction), acute Wernicke's encephalopathy (especially horizontal vestibular function[110]), tumors, head trauma, neuropathies, and neurodegenerative processes (e.g., certain spinocerebellar ataxias [SCAs], especially Friedreich's ataxia, SCA3 [Machado–Joseph], and cerebellar ataxia, neuropathy, vestibular areflexia syndrome [CANVAS]).[108,111,112] However, in more than half of cases of BVL, the etiology remains unknown.[111]

Physical therapy to promote compensation and reliance on visual and proprioceptive systems is the mainstay of treatment.[113] Vestibular suppressant medications should be avoided.[108]

Acoustic Neuroma: Acoustic neuromas (or vestibular schwannoma) are rare tumors with an incidence estimated to be between 1 and 2 in 100,000 persons per year.[114] Acoustic neuromas originate from the nerve sheath-producing Schwann cells which surround the vestibular nerve. Patients with acoustic neuroma typically present with unilateral progressive hearing loss and tinnitus with chronic imbalance due to ipsilateral VOR impairment. Ocular motor examination may reveal ipsilateral gaze-evoked nystagmus and contralateral vestibular nystagmus, a combination known as Burns nystagmus.[22] In patients with acoustic neuroma, nystagmus is often induced by hyperventilation (Table 1). An audiogram and contrast-enhanced MRI with an internal auditory canal protocol should be considered if acoustic neuroma is suspected clinically (Table 2). Approximately half of all acoustic neuromas are treated by surgery, about a quarter with radiation, and about a quarter are observed.[115]

Cerebellar Diseases: Disorders affecting the vestibulocerebellum (which includes the flocculus/paraflocculus and uvula/nodulus) are often associated with characteristic ocular motor deficits, and patients may seek care due to dizziness, vertigo, unsteadiness or oscillopsia.[22] Spontaneous downbeat nystagmus (DBN) is often noticed with flocculus/paraflocculus lesions, which in many patients may be due to loss of inhibition of the anterior semicircular canal pathways, resulting from floccular Purkinje cell dysfunction.[22] Other theories for DBN include up–down asymmetry in cerebellar Purkinje cells, as well as vertical pursuit or otolithic asymmetry. The flocculus/paraflocculus normally improves the neural integrator (gaze-holding) function of brainstem nuclei (nucleus prepositus hypoglossi-medial vestibular nucleus complex horizontally and interstitial nucleus of Cajal vertically), so that a leaky neural integrator will cause gaze-evoked nystagmus (GEN). For example, when a patient with a severe cerebellar disorder looks to the right, the gaze-holding mechanism will not be able to keep the eyes in eccentric gaze on the target. This results in a slow phase (leftward) drift back to center, with a subsequent rightward fast phase to move the eyes back to the visual target. The nystagmus becomes left-beating when the patient looks to the left, and vertical nystagmus may be present in the vertical gaze as well. Along with GEN, rebound nystagmus is often observed as well. For example, there is right-beating nystagmus in right gaze, and when the patient returns to primary gaze, transient left-beating (rebound) nystagmus can be seen. Saccadic pursuit and saccadic vestibular-ocular reflex suppression (VORS) are also seen due to a decrease in pursuit gain. Pursuit and VORS will be proportionally saccadic, unless the VOR is lost (e.g., bilateral vestibular loss), in which case VORS will look smoother than pursuit because there will be no VOR to suppress. Positional testing to elicit nystagmus can identify patterns diagnostic of cerebellar disease, such as positional DBN in multiple system atrophy or conditions primarily involving the vestibulocerebellum.[116,117] Hyperventilation and head shaking can also enhance or produce downbeat nystagmus in cerebellar disease. The neurological examination should emphasize the cerebellar exam and gait instability. With subacute onset of cerebellar dysfunction a paraneoplastic process should be considered, especially in elderly patients. With chronic symptoms, one should mainly consider toxic, nutritional, and neurodegenerative conditions.

Oculopalatal Tremor: Hypertrophic olivary degeneration manifests as oculopalatal tremor, where palatal tremor is synchronous with pendular nystagmus.[22,118] The most bothersome consequence of oculopalatal tremor is oscillopsia related to the pendular nystagmus, which can be difficult to treat. Oculopalatal tremor develops weeks to months after a structural brainstem or cerebellar lesion affecting the triangle of Guillain–Mollaret, referring to the pathway connecting the dentate nucleus, red nucleus, and inferior olivary nucleus.[22,118] A brainstem hemorrhage (commonly due to a pontine cavernoma) involving the central tegmental tract is the most common responsible lesion. Another syndrome termed progressive ataxia and palatal tremor (PAPT) has also been described; in this presumed neurodegenerative syndrome, a progressive ataxia and palatal/oculopalatal tremor develops in patients without history of a structural brainstem or cerebellar lesion Box 6.[119–121]

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