Direction of Nystagmus in Vestibular Neuritis
In vestibular neuritis, the spontaneous nystagmus beats horizontally toward the unaffected ear (away from the affected ear), with a rotational component. 1
Pathophysiology and Clinical Presentation
Vestibular neuritis is characterized by:
- Acute onset of rotatory vertigo lasting several days
- Horizontal spontaneous nystagmus with a rotational component beating toward the unaffected ear
- Pathologic head-impulse test toward the affected ear
- Deviation of the subjective visual vertical toward the affected ear
- Postural imbalance with falls toward the affected ear
- Nausea and vomiting 1
This directional pattern occurs because the affected ear has reduced vestibular function, creating an imbalance where the healthy ear's tonic neural activity becomes relatively dominant, driving the slow phase of nystagmus toward the affected side. The fast phase (the visible component of nystagmus that we observe clinically) beats in the opposite direction - toward the unaffected ear.
Diagnostic Testing
To confirm vestibular neuritis and determine the affected side:
- Head impulse test: Will show impaired vestibulo-ocular reflex (VOR) toward the affected ear
- Caloric testing: Reveals ipsilateral deficit of the VOR on the affected side
- Video head impulse test (vHIT): Can identify selective damage to specific vestibular nerve branches 2
Recovery Nystagmus
An important clinical caveat is the phenomenon of recovery nystagmus:
- During recovery, the direction of nystagmus may reverse and beat toward the affected ear
- This is centrally mediated and indicates ongoing compensation
- Typically occurs days to weeks after initial presentation
- Can be confused with a new pathology if not recognized 3
Differential Diagnosis
Vestibular neuritis must be differentiated from other causes of vertigo:
- Benign paroxysmal positional vertigo (BPPV)
- Vestibular migraine
- Ménière's disease
- Central causes (vestibular pseudoneuritis due to brainstem or cerebellar lesions)
- Stroke in the posterior circulation 1, 4
Management Considerations
The diagnosis of vestibular neuritis is primarily clinical and a diagnosis of exclusion. Early treatment with corticosteroids may improve recovery of peripheral vestibular function, with studies showing a recovery rate of 62% within 12 months 1.
Remember that vestibular neuritis is the third most common cause of peripheral vestibular vertigo, with an annual incidence of 3.5 per 100,000 population 1. The most likely etiology is reactivation of latent herpes simplex virus type 1 (HSV-1) infection, though enteroviruses and other viral agents have also been implicated 5, 2.