Vestibular Neuritis

Acute unilateral peripheral vestibular failure without auditory symptoms, presenting as acute vestibular syndrome. When hearing is involved the condition is termed labyrinthitis.

Aetiology and pathology

Reactivation of latent herpes simplex virus type 1 within the vestibular ganglion is the leading hypothesis, supported by the presence of viral DNA in vestibular ganglia at autopsy and by inflammatory infiltrate and axonal degeneration in histopathological specimens.

The superior vestibular nerve is affected in the majority, which is anatomically explained: it travels in a longer, narrower bony channel with more bony spicules than the inferior division, making it more vulnerable to compression from inflammatory swelling. The superior division supplies the horizontal and anterior semicircular canals and the utricle, and the inferior division supplies the posterior canal and the saccule.

This distribution explains why the head impulse test is abnormal in the horizontal plane, why cervical vestibular evoked myogenic potentials, which test the saccule and inferior nerve, are often preserved, and why patients frequently develop posterior canal benign paroxysmal positional vertigo afterwards, since utricular otoconia are shed into an intact posterior canal.

Course

Acute severe vertigo lasting 24 to 72 hours, gradually improving over 1 to 2 weeks, with central compensation over weeks to months. Around 30 to 50 percent have persistent measurable vestibular hypofunction, and a substantial minority develop chronic dizziness, most often persistent postural perceptual dizziness. Recurrence of true vestibular neuritis is uncommon at around 2 to 5 percent, so recurrent episodes should prompt reconsideration of the diagnosis.

• Sudden onset severe continuous rotational vertigo, maximal within hours and persisting for days.
• Severe nausea and vomiting, often requiring admission for rehydration.
• Oscillopsia and inability to focus.
• Gait instability with a tendency to fall toward the affected side.
• Symptoms worsened by any head movement, but present at rest, which distinguishes this from positional vertigo.
• No hearing loss, tinnitus or aural fullness. Their presence indicates labyrinthitis or another diagnosis.
• No headache, no focal neurological symptoms.
• A preceding upper respiratory illness in a proportion.

Examination findings

• Spontaneous horizontal torsional nystagmus with the fast phase beating away from the affected ear, obeying Alexander law by increasing on gaze in the direction of the fast phase. It is suppressed by visual fixation and enhanced with Frenzel goggles.
• Positive head impulse test toward the affected side with a corrective catch up saccade.
• Absent skew deviation on cover uncover testing.
• Unsteady Romberg with falling toward the affected side, but the patient can still stand and walk with assistance.
• Normal otoscopy and normal hearing.

The essential task is to separate this benign condition from posterior circulation stroke, which presents identically in around 25 percent of acute vestibular syndrome presentations in patients with vascular risk factors.

The HINTS examination, performed only in patients with continuous vertigo and nystagmus at the time of examination:

• Head Impulse: a normal head impulse test in a patient with acute vestibular syndrome is a central sign, since the peripheral system is intact.
• Nystagmus: direction changing nystagmus on eccentric gaze, or purely vertical or torsional nystagmus, is central.
• Test of Skew: vertical ocular misalignment on cover uncover testing is central.

A peripheral pattern requires all three of an abnormal head impulse, unidirectional horizontal nystagmus, and absent skew. Any one central finding mandates urgent imaging. This examination outperforms early magnetic resonance imaging with diffusion weighted sequences, which has a false negative rate of 10 to 20 percent in the first 24 to 48 hours for small posterior fossa infarcts.

Additional central red flags: severe headache or neck pain suggesting dissection, inability to sit or walk unaided, other cranial nerve deficits, limb ataxia, dysarthria, dysphagia, and new deafness which may indicate anterior inferior cerebellar artery infarction.

Investigations

• Pure tone audiometry in all patients, to confirm normal hearing and distinguish from labyrinthitis.
• Video head impulse testing quantifying vestibulo ocular reflex gain, with gain below 0.8 and refixation saccades indicating hypofunction.
• Caloric testing showing unilateral weakness, usually performed after the acute phase.
• Vestibular evoked myogenic potentials to determine superior versus inferior nerve involvement.
• Magnetic resonance imaging with diffusion weighted sequences for any central sign, any patient with vascular risk factors and an inconclusive bedside examination, and for atypical or non improving cases. Repeat imaging at 48 to 72 hours if initially negative but clinical suspicion of stroke remains.
• Blood glucose, blood pressure, electrocardiogram and vascular risk assessment in the older patient.

Differential diagnosis

• Posterior circulation stroke.
• Labyrinthitis: identical but with hearing loss.
• Ménière disease: episodic and recurrent with fluctuating hearing.
• Vestibular migraine: recurrent, with migraine features, and often shorter.
• Benign paroxysmal positional vertigo: brief positional episodes, no vertigo at rest.
• Multiple sclerosis: young patient, other neurological features, characteristic imaging.
• Ramsay Hunt syndrome: pain, vesicles, facial palsy.
• Drug intoxication, particularly anticonvulsants and alcohol, which produce gaze evoked nystagmus.

Three components: symptomatic relief for a strictly limited period, consideration of corticosteroids, and early vestibular rehabilitation. The commonest management error is prolonged prescription of vestibular sedatives, which prevents central compensation and converts an acute self limiting illness into chronic dizziness.

Acute symptomatic treatment, 48 to 72 hours maximum

• Prochlorperazine 12.5 mg intramuscularly for the acute presentation, then 5 to 10 mg orally three times daily or 3 mg buccally twice daily. Watch for acute dystonic reactions in the young and extrapyramidal effects in the elderly.
• Cyclizine 50 mg orally, intramuscularly or intravenously three times daily.
• Promethazine 25 mg orally or intramuscularly, which is more sedating.
• Ondansetron 4 to 8 mg orally or intravenously for vomiting, noting QT prolongation and constipation.
• Diazepam 2 to 5 mg for severe distress, used very sparingly.
• Intravenous rehydration with 0.9 percent sodium chloride where vomiting prevents oral intake.
• Stop all vestibular sedatives by day 3 without exception, and explain to the patient that stopping them is part of the treatment.

Corticosteroids

• Prednisolone 1 mg/kg orally daily, maximum 60 to 80 mg, for 5 days followed by a taper over 15 days, or methylprednisolone using an equivalent tapering regimen.
• Corticosteroids improve the recovery of caloric responses at 12 months, but the evidence that they improve symptomatic or functional outcomes is weak, and analyses have not demonstrated a clear clinical benefit over vestibular rehabilitation alone.
• Reasonable to offer within the first 3 days in patients with severe disease and no contraindication, with a clear explanation of the uncertain benefit.
• Monitor glucose in diabetics, add gastroprotection where indicated, and avoid in active infection, uncontrolled hypertension and psychosis.

Antivirals

Aciclovir and valaciclovir, alone or combined with corticosteroid, have not shown benefit and are not recommended.

Vestibular rehabilitation, which is the treatment that determines long term outcome

• Begin as soon as vomiting settles, typically within 48 to 72 hours.
• Encourage early mobilisation rather than bed rest. Bed rest delays compensation.
• Gaze stabilisation exercises: fixating a target while moving the head horizontally then vertically, starting at 30 seconds and building to 1 to 2 minutes, performed three times daily.
• Habituation exercises repeating the movements that provoke symptoms.
• Balance and gait training progressing from a wide to a narrow base, from eyes open to eyes closed, and from firm to compliant surfaces.
• Formal supervised programmes for the elderly, for those with visual or proprioceptive impairment, and for anyone still symptomatic at 4 weeks.
• Explain clearly that exercises will provoke symptoms initially and that this is the mechanism by which they work. Patients who stop because of symptom provocation do not compensate.

Follow up and complications

• Review at 4 to 6 weeks. Most patients are substantially better.
• Around 10 to 20 percent develop posterior canal benign paroxysmal positional vertigo in the weeks after the acute illness, from otoconia shed by the damaged utricle. New brief positional vertigo in a recovering patient should be tested for with the Dix Hallpike and treated with an Epley manoeuvre, not attributed to incomplete recovery.
• Persistent dizziness beyond 3 months, particularly with visual motion sensitivity and worsening in busy environments, indicates persistent postural perceptual dizziness. Treat with vestibular rehabilitation, selective serotonin reuptake inhibitors and cognitive behavioural therapy rather than further vestibular suppressants.
• Screen for and treat anxiety, which is common after an acute vertigo episode and is a strong predictor of chronic dizziness.
• Advise on driving. Patients should not drive while symptomatic, and should inform the licensing authority where local rules require.