Clinical characteristics: signs and symptoms
The main symptoms of acute unilateral vestibular deficit are violent rotatory vertigo, apparent movement of the visual surrounding (oscillopsia), gait and postural imbalance with a tendency to fall toward the side of the affected ear, as well as nausea and vomiting. All of these symptoms have an acute or subacute onset and last for many days or a few weeks. To make the diagnosis, you must first exclude the possibility of hearing disorders or—even more relevant—other neurological deficits, in particular those originating from the brainstem or cerebellum. Therefore, it is important to note that you have to explicitly ask the patient for symptoms that may arise from the inner ear, brainstem, or cerebellum (1). There are no typical antecedent signs or triggers, although some patients have occasional spells of vertigo a few days before (2). Since the patients’ complaints are exacerbated by any movements of the head, they intuitively seek peace and quiet.
Key signs and symptoms of vestibular neuritis are: 1) an acute/subacute onset of sustained rotational vertigo with pathological adjustments of the subjective visual vertical toward the affected ear; 2) peripheral vestibular spontaneous nystagmus with a torsional component toward the non-affected ear, which can be suppressed by visual fixation; 3) a pathological head-impulse test (3); 4) postural imbalance with falls toward the affected ear (positive Romberg test); and 5) nausea and vomiting (Figure 19.1) 4–6). Ocular motor evaluation reveals an incomplete ocular tilt reaction, apparent horizontal saccadic pursuit, and an increase of the intensity of the nystagmus when looking in the direction of the fast phase. All of these symptoms are secondary to the peripheral vestibular spontaneous nystagmus, which indicates a vestibular tone imbalance in the yaw (horizontal) and roll (torsional) planes between the two labyrinths.
Peripheral vestibular spontaneous nystagmus
The nystagmus in vestibular neuritis is horizontal due to the involvement of the horizontal semicircular canal. It has a torsional component due to involvement of the vertical superior canal (beating counterclockwise-left or clockwise-right from the patient’s point of view) (7, 8). The three-dimensional features of the spontaneous nystagmus in vestibular neuritis, i.e. the horizontal, vertical, and torsional components as well as the dynamic deficit of the vestibulo-ocular reflex (VOR) of the horizontal, anterior, and posterior semicircular canals (see later), have been measured by means of the scleral-coil technique and analysed by vector analysis (7). These measurements support the earlier view (9) that vestibular neuritis is a partial rather than a complete unilateral vestibular lesion. It affects the superior division of the vestibular nerve (innervating the horizontal and anterior semicircular canals, the maculae of the utricle, and the anterosuperior part of the saccule), which has its own path and ganglion (10, 11). The inferior vestibular nerve (innervating the posterior semicircular canal and the posteroinferior part of the saccule) is spared (7). This has twofold implications: first, with respect to clinical findings, it explains why patients with vestibular neuritis can suffer from benign paroxysmal positioning nystagmus of the posterior canal (9, 12, 13); second, it explains the pathophysiology and aetiology of the disorder (see page [link]). It rarely happens that only the inferior division of the vestibular nerve is affected which then causes inferior vestibular neuritis (14–16). In these patients the horizontal semicircular canal (with normal caloric irrigation) and anterior semicircular canal function normally, whereas the posterior canal and the saccule are impaired, as was demonstrated by the three-dimensional head-impulse test (14) and vestibular-evoked potentials (17).
Peripheral vestibular spontaneous nystagmus in vestibular neuritis is typically reduced in amplitude during fixation, because visual fixation suppresses the VOR. The error signal for the suppression is the retinal slip. This visual fixation suppression of the spontaneous nystagmus, however, is only possible if the relevant central structures in the brainstem and cerebellum are intact. On the other hand, the intensity of a peripheral vestibular spontaneous nystagmus is enhanced by eye closure (you can see the nystagmus when looking at the eyelids or even feel it when you touch the eyelids with your fingertips), Frenzel glasses (+16 dioptres), and during convergence. According to Alexander’s law, amplitude and slow-phase velocity are increased with gaze shifts in the direction of the fast phase, and decreased with gaze shifts in the direction of the slow phase of the nystagmus. This may mimic unilateral gaze-evoked nystagmus in a patient with moderate spontaneous nystagmus that is completely suppressed by visual fixation straight ahead, but it is still present when the gaze is directed toward the fast phase.
Head impulse test
A suspected diagnosis of vestibular neuritis is supported by demonstrating a unilateral deficit of the VOR by means of the head impulse test (3, 18–20). When the head is rapidly rotated toward the side with the lesion, the eyes move with the head and the patient has to make a compensatory re-fixation saccade. This indicates a dynamic unilateral high-frequency deficiency of the VOR which persists if the peripheral vestibular function does not recover. Since the diagnosis of a unilateral dynamic deficit of the VOR by the bedside head impulse test is not always reliable, a video head impulse test can be useful (21).
Incomplete ocular tilt reaction and the bucket test
An incomplete ocular tilt reaction with ocular torsion and perceived tilts of the subjective visual vertical occurs in most patients with vestibular neuritis (22). Nowadays a simple bedside device, the so-called bucket test (23), can be used to easily measure the subjective visual vertical, which is the most sensitive parameter for an acute lesion of the vestibular system (Figure 19.2).
Although reported in the older literature (24, 25), patients with vestibular neuritis do not have a skew deviation/vertical divergence. This typically occurs in vestibular pseudoneuritis (19) and can also be found in a complete de-afferentation, which occurs in zoster oticus (26). An ocular tilt reaction indicates a vestibular tone imbalance in the roll plane induced by involvement of the anterior semicircular canal or otolith function, or both.
The principal diagnostic marker of vestibular neuritis is a peripheral vestibular deficit on the affected side. Caloric testing shows a hypo- or unresponsiveness of the tested and affected horizontal canal in vestibular neuritis. Since there is a large intersubject variability of the nystagmus induced by caloric irrigation and a small intraindividual variability of the response of the right and the left labyrinths in healthy subjects, ‘Jongkees’s formula for vestibular paresis’ (27):(((R30° + R44°) − (L30° + L44°))/ (R30° + R44° + L30° + L44°)) × 100
should be used to determine its presence. In this formula, for instance, R30° is the mean peak slow-phase velocity during caloric irrigation with 30°C water. Vestibular paresis is usually defined as greater than 25% asymmetry between the two sides (28). This formula allows a direct comparison of the function of the horizontal semicircular canals of both labyrinths, which is important due to the large interindividual variability of caloric excitability.
Cervical and ocular vestibular-evoked myogenic potentials
In response to loud clicks, cervical vestibular-evoked myogenic potentials (cVEMP) can be recorded from the sternocleidomastoid muscles (29, 30). There is good evidence that cVEMPs originate in the medial (striola) area of the saccular macula (31). Cervical VEMP allow examination of the function of the saccule and, thereby, of the inferior vestibular nerve. VEMPs are preserved in at least two-thirds of the patients with vestibular neuritis (32, 33). This is because the inferior part of the vestibular nerve is spared in most patients (see later), and it supplies the posteroinferior part of the saccule and posterior canal.
Intense air-conducted sound as well as bone-conducted vibration (nowadays preferred with the so-called mini-shaker) can elicit ocular VEMPs (oVEMPs). In ten patients with vestibular neuritis and normal saccular and inferior vestibular nerve function, the oVEMP n10 amplitude was reduced or absent in response to air-conducted sound. This indicates the involvement of utricular receptors and thereby the crossed utriculo-ocular pathway (34).
There is good evidence that vestibular neuritis is caused by a viral inflammation; however, this has not yet been proven (35–37). The following arguments are presented in support of a viral aetiology. First, the vestibular nerve histopathology in cases of vestibular neuritis (38) is similar to that seen in single cases of herpes zoster oticus, when temporal bone histopathology was available. Second, an animal model of vestibular neuritis was developed by inoculating herpes simplex virus 1 (HSV-1) into the auricle of mice (39, 40). Third, HSV-1 DNA was repeatedly detected in about two-thirds of autopsied human vestibular ganglia by polymerase chain reaction (PCR) (41, 42) (Figure 19.3); furthermore, the ‘latency associated transcript’ was found in about 70% of human vestibular ganglia (43) as well as infiltration of CD8+ T cells (44). All these findings indicate that the vestibular ganglia like other cranial nerve ganglia are latently infected by HSV-1 (45–47). A similar aetiology is also assumed for Bell’s palsy and strongly supported by the demonstration of HSV-1 DNA in the endoneural fluid of affected subjects (48).
If HSV-1 is the most likely candidate, it can be assumed to reside in a latent state in the vestibular ganglia, e.g. in the ganglionic nuclei as has been reported in other cranial nerves (19, 45, 49–53). Due to intercurrent factors, the virus suddenly replicates and induces inflammation and oedema, thereby causing secondary cell damage of the vestibular ganglion cells and axons in the bony canals. The canal of the superior vestibular nerve is longer and has more speculae (54), whereas the posterior semicircular canal is innervated by an additional anastomosis (55). This difference may explain why the posterior canal is often spared.
Epidemiology, spontaneous course, recurrences, and complications
Vestibular neuritis has an incidence of about 3.5 per 100,000 persons (56). It is the third most common cause of peripheral vestibular disorders in our neurological dizziness unit (benign paroxysmal positioning vertigo ranks first, Ménière’s disease second). It accounts for about 7% of the patients (57). The usual age of onset is between 30–60 years (58), and age distribution plateaus between 40–50 years (56). There is no significant sexual difference.
The onset of the disease is usually sudden. Patients feel severely ill and prefer to stay immobilized in bed for about 1–3 days. After 5–7 days spontaneous nystagmus is largely suppressed by fixation in the primary position, although—depending on the severity of the canal palsy—it is still present for 2–3 weeks with Frenzel glasses and during lateral gaze directed away from the lesion. After recovery of peripheral vestibular function, spontaneous nystagmus transiently reverses its direction in some patients (recovery nystagmus), i.e. when the centrally compensated lesion regains function. Recovery nystagmus then reflects a tone imbalance secondary to compensation. Bechterew’s phenomenon, a reversal of spontaneous nystagmus that occurs after contralateral labyrinthectomy in animals or humans (59, 60), is produced by a similar mechanism. After 1–6 weeks most of the patients feel symptom free, even during slow body movements, but actual recovery depends on if and how quickly functional restitution of the vestibular nerve occurs during ‘central compensation’ (61) and possibly on how much physical exercise the patient has done. Rapid head movements, however, may still cause slight oscillopsia of the visual scene and impaired balance for a second in those who do not regain normal labyrinthine function. This explains why only 34 (57%) of 60 patients with vestibular neuritis reported complete relief from subjective symptoms at long-term follow-up (62), a figure that roughly corresponds to the 50–70% complete recovery rate of labyrinthine function assessed by caloric irrigation (62–64).
Numerous, mostly retrospective rather than prospective, studies have investigated the rate of complete or incomplete recovery of vestibular function as measured by the nystagmus response to caloric irrigation (57, 65). These studies are difficult to compare because of their different study design, the number of patients included, diagnostic criteria, definition of recovery, and duration of follow-up. This explains the great divergence in the numbers of complete or incomplete vestibular recovery following acute vestibular neuritis. The average recovery, which is based on ten studies (Figure 19.4), shows a tendency to functional improvement not only in the first few months but up to 10 years afterwards (57). Tests for ocular torsion, subjective visual vertical, and vestibular-evoked myogenic potentials revealed that otolith function appears to improve more rapidly than canal-related test abnormalities at the short-term follow-up (66).
In a long-term follow-up study (5.7–20.5 years, mean 9.8 years) on a total of 103 patients with vestibular neuritis, only two patients (1.9%) had developed a second vestibular neuritis 29–39 months after the first (67). It affected the contralateral ear in both patients and caused less severe, distressing vertigo and postural imbalance. In another study on 131 patients the recurrence was 10.7% (68).
In 10–15% of patients with vestibular neuritis a typical, benign paroxysmal positioning vertigo develops in the affected ear within a few weeks (9, 13, 68, 69). It is possible that the otoconia loosen during the additional inflammation of the labyrinth (HSV-1 DNA was also found in the human labyrinth (70)), and this eventually results in canalolithiasis. Patients should be warned about this possible complication, because there are therapeutic liberatory manoeuvres that can quickly free them of their complaints. The second important complication is that vestibular neuritis can develop into a secondary phobic postural vertigo (71, 72). A recent study shows that the transition from vestibular neuritis to phobic postural vertigo can also be diagnosed by artificial neural network posturography (73). The traumatic experience of a persisting organic rotatory vertigo leads to fearful introspection, resulting in a somatoform, fluctuating, and persistent postural vertigo, which is reinforced in specific situations and culminates in a phobic behaviour of avoidance.
Differential diagnosis and other clinical problems
Topographically, dysfunctions or lesions in the brainstem and/or cerebellum (so-called vestibular pseudoneuritis) as well as other peripheral vestibular disorders may mimic vestibular neuritis. In other words: there is no pathognomonic test or sign for vestibular neuritis as a clinical entity (1, 18, 19, 74). In a strict sense, only an acute unilateral peripheral vestibular hypofunction with horizontal semicircular canal paresis can be diagnosed by the head-impulse test and caloric irrigation.
Central lesions mimicking vestibular neuritis
A lesion that occurs in a small area in the lateral medulla including the root entry zone of the vestibular nerve and the medial and superior vestibular nuclei may be confused with lesions of the peripheral vestibular nerve or labyrinths. We have seen several patients with multiple sclerosis who have pontomedullary plaques or small lacunar ischemia or infarctions in the territory of the anterior inferior cerebellar artery (AICA) (Figure 19.5) (75) at the root entry zone of the VIIIth nerve. This leads to ‘fascicular nerve lesion’, which mimics vestibular neuritis: ‘vestibular pseudoneuritis’. A small lacunar infarction of the vestibular nuclei (76) or the dorsolateral pons (77) may also mimic vestibular neuritis.
The differential diagnosis between central and peripheral causes of unilateral vestibular loss is simple, if the patient has obvious additional brainstem signs. If this is not the case, differential diagnosis is indeed difficult. Therefore, in several studies the clinical signs to differentiate vestibular neuritis from central ‘vestibular pseudoneuritis’ in the acute situation were correlated, and the final diagnosis was assessed by neuroimaging (18, 19, 78, 79). None of the isolated signs (head impulse test, saccadic pursuit, gaze-evoked nystagmus, subjective visual vertical) is reliable. There are two exceptions: in most studies skew deviation or a normal head impulse test in a patient with acute onset of vertigo and nystagmus was a specific, but non-sensitive sign for vestibular pseudoneuritis (18, 19, 78). A combination of the different clinical signs (skew deviation, head impulse test, gaze-holding function, fixation versus peripheral vestibular spontaneous nystagmus, and smooth pursuit eye movements), however, increased the sensitivity and specificity to more than 90% (18, 19, 78, 79).
Cerebellar infarction may also mimic vestibular neuritis, if it occurs in the territory of the posterior inferior cerebellar artery (PICA; 80–83), especially if it is an isolated nodular infarction (84). It may also cause an incomplete ocular tilt reaction (85), in particular, if the dentate nucleus is involved (86). This could make the differential diagnosis even more difficult. Infarction in the territory of the anterior inferior cerebellar artery (AICA) may also mimic vestibular neuritis, but it is most often associated with AICA unilateral hearing loss (due to cochlear ischemia) and additional brainstem signs (88, 89). All in all, brainstem or cerebellar infarctions may cause isolated vertigo and a pathological Romberg sign, but clinical examination of eye movements and hearing will allow its differentiation from vestibular neuritis and vestibular pseudoneuritis.
Acute attacks of vestibular migraine (89, 90) may also mimic vestibular neuritis, because they may be associated with a rotatory vertigo and horizontal-torsional nystagmus. Accompanying symptoms and the course of the disease help to differentiate between the two entities.
Peripheral vestibular lesions
The differential diagnosis of peripheral labyrinthine and vestibular nerve disorders mimicking vestibular neuritis includes numerous rare conditions. Nevertheless, extensive laboratory examinations, lumbar puncture, and computed tomography/magnetic resonance imaging (MRI) are not part of the routine diagnostics of vestibular neuritis for two reasons: 1) the rareness of these disorders and 2) typical additional signs and symptoms indicative of other disorders. An initial monosymptomatic vertigo attack in Menière’s disease or a short attack in vestibular paroxysmia (91, 92) can be confused with vestibular neuritis in a patient admitted to the hospital in an acute stage. The shortness of the attack and the patient’s rapid recovery, however, allow differentiation. During the course of the disease almost all patients with Ménière’s disease develop hypoacusis, tinnitus, or aural fullness in the affected ear, which also allows differentiation. An initially burning pain and blisters as well as hearing disorders and facial paresis are typical for herpes zoster oticus (Ramsay–Hunt syndrome) (in such cases acyclovir or valacyclovir is indicated). It has to be pointed out that there may be a skew deviation in herpes zoster oticus due to the complete unilateral peripheral vestibular deficit, i.e. of the superior and inferior parts of the vestibular nerve (26) and—contrary to vestibular neuritis—a contrast enhancement of the VIIIth cranial nerve. Cogan syndrome (often overlooked) is a severe autoimmune disease accompanied by interstitial keratitis and audiovestibular symptoms (hearing disorders are very prominent). It occurs most often in young adults and responds, in part only temporarily, to the very early administration of high doses of corticoids (1000 mg per day for 3–5 days, then slowly tapered off) or—like other autoimmune diseases of the inner ear—to a subsequent combination of steroids and cyclophosphamide.
Rare variants of vestibular neuritis have been described, e.g. inferior vestibular neuritis (here there is a selective deficit of the posterior canal combined with sparing of the lateral and anterior canals) (14, 15) and a form in which a dysfunction of the posterior canal is combined with one of the cochlea. The latter probably does not have a viral but rather a vascular aetiology, since both structures have a common area of vascular supply.
Vestibular schwannomas, which arise in the myelin sheaths of the vestibular part of the VIIIth nerve, often cause only vertigo, a tendency to fall, and nystagmus if the pontomedullary brainstem and the flocculus are compressed, and the increasing peripheral tone difference can no longer be neutralized by central compensation. The main symptom is a slowly progressive unilateral reduction of hearing without any identifiable otological cause. This is combined with a caloric hypoexcitability or non-excitability. There is rarely also a loss of hearing as well as recurrent attacks of vertigo in cases of a purely intracanalicular dilatation, which can be confirmed by MRI and treated early by microsurgery or with the ‘gamma knife’.
The management of vestibular neuritis involves: 1) symptomatic treatment with antivertiginous drugs (e.g. dimenhydrinate, scopolamine, or in severe cases benzodiazepines) to attenuate vertigo, dizziness, and nausea/vomiting; 2) ‘causal’ treatment with corticosteroids to improve recovery of peripheral vestibular function; and 3) physical therapy (vestibular exercises and balance training) to improve central vestibular compensation (93).
During the first 1–3 days, when nausea is pronounced, vestibular sedatives such as antihistamine dimenhydrinate (50–100 mg every 6 h) or the anticholinergic scopolamine can be administered. Their major side effect is general sedation. Transdermal application of scopolamine hydrobromide avoids some of the side effects of the conventional means of administration. The most probable sites of primary action are the synapses of the vestibular nuclei, which exhibit a reduced discharge and diminished neural reaction to body rotation. These drugs should not be given for more than 3 days, because they evidently prolong the time required to achieve central compensation (94, 95).
Based on the assumption that vestibular neuritis is caused by the reactivation of a latent HSV-1 infection, a prospective, randomized, double-blind trial was conducted to determine whether steroids, antiviral agents, or a combination of the two might improve outcome in vestibular neuritis (96). This study with a placebo, methylprednisolone, valacyclovir, and methylprednisolone plus valacyclovir groups out of a total 114 patients showed that monotherapy with steroids suffices to significantly improve the peripheral vestibular function of patients with vestibular neuritis; there was no evidence for synergy between methylprednisolone and valacyclovir (Figure 19.6 ) (96). Glucocorticoids (6-methylprednisolone) should be given within 3 days after symptom onset and for 3 weeks (initially 100 mg/day and then tapered off by 20 mg every 3 days). These findings are supported by a more recent study (97). It must, however, be mentioned that due to the few appropriate studies, treatment with steroids is so far not generally recommended (98). As in Bell’s palsy, the benefit of steroids might be due to their anti-inflammatory effects, which reduce the swelling and cause a mechanical compression of the vestibular nerve within the temporal bone.
A gradual programme of physical exercise under the supervision of a physiotherapist improves the central vestibular compensation of a peripheral deficit. First, static stabilization is concentrated on, and then dynamic exercises are done for balance control and gaze stabilization during eye–head–body movements. It is important that the degree of difficulty of exercises for equilibrium and balance be successively increased above normal levels, both with and without visual stabilization. The efficacy of physiotherapy in improving central vestibulospinal compensation in patients with vestibular neuritis has been proven in a prospective, randomized, and controlled clinical study (99) and confirmed in a meta-analysis (100).
Vestibular neuritis is the third most frequently occurring peripheral vestibular disorder. Its diagnosis is based on the patient history (acute onset of rotatory vertigo) and clinical bedside examination (to exclude any central vestibular, ocular motor, or cerebellar dysfunction) as well as caloric irrigation, which shows a hypo- or unresponsiveness of the affected horizontal canal. The use of three-dimensional recordings of eye movements with a vector analysis of the peripheral vestibular spontaneous nystagmus and head-impulse test in combination with cVEMPs and oVEMPs is helpful for identifying the different parts of the vestibular nerve affected (it is most often the superior vestibular nerve which then affects the horizontal and anterior semicircular canals and utricles). There is good evidence that vestibular neuritis is caused by the reactivation of a latent HSV-1 infection, although further work still has to be done. This is also true for its treatment, because there is only limited evidence so far that the outcome can be improved by the early administration of corticosteroids.
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