What is vestibular neuronitis?

Vestibular neuronitis is an acute peripheral vestibulopathy and the second most common cause of peripheral vestibular vertigo after benign paroxysmal positional vertigo. The signs and symptoms of vestibular neuronitis are acute onset of sustained rotatory vertigo, horizontal spontaneous nystagmus toward the unaffected ear with a torsional component, lateropulsion i.e. falls with the eyes closed toward the affected ear and nausea & vomiting. The caloric testing (usually not required for clinical diagnosis) invariably shows ipsilateral canal paresis but the latter can be interpreted with a carefully performed Halmagyi head thrust test.

The video clipping below shows a positive Halmagyi head thrust test to the right.


The video below shows a negative Halmagyi head thrust test to same patient's left.

Herpes simplex virus type 1 (HSV-1) DNA has been detected on autopsy with the use of polymerase chain reaction in human vestibular ganglia. It is speculated that after primary infection of the epithelium (apthous stomatitis), HSV-1 enters the axon terminals and is carried by axonal transport to sensory neurons of the human trigeminal ganglia and geniculate ganglia. In these ganglia it remains latent until certain stimuli reactivate HSV-1 by switching its viral state from latent to lytic. During reactivation in the trigeminal ganglion, virus particles can be transported back to the entry site, causing herpes labialis. In contrast, when reactivated in the geniculate ganglion, the virus may spread via the faciovestibular anastomosis to the vestibular ganglia (Scarpa's ganglion) causing vestibular neuronitis. Vestibular neuronitis affects only a part of the vestibular trunk, usually the superior division (horizontal saccular canal paresis), which travels separately and has its own ganglion whereas the inferior part (the posterior semicircular canal) is mostly spared. A very occasional patient may have a combined superior and inferior vestibular neuronitis. Most patients recover well from vestibular neuritis, even without treatment. Nonetheless, studies suggest that a course of oral steroids in the form of oral methylprednisolone (100 mg/day, doses tapered by 20 mg every third day) for three weeks accelerates the recovery of vestibular function but whether steroids influence long-term outcome is less certain. Thus, until more data become available, it is reasonable to treat otherwise healthy individuals who present within 3 days of onset with steroids and to withhold steroids from those who are at higher risk of complications. Antiemetics and vestibular suppressants are useful acutely but should not be given for more than three days because their prolonged use impedes the process of central vestibular compensation. In evaluating a patient with an acute vestibular syndrome, it is important not to miss a central cause, such as a brainstem or cerebellar infarct or hemorrhage, which could be life-threatening and the definitive central signs may not always be present. Thus, any patient thought to have vestibular neuritis but has significant vascular risk factors should be evaluated for a possible posterior circulation stroke by getting a magnetic resonance imaging on a 1.5 Tesla machine with instructions to get thin three millimeter axial as well coronal cuts of medulla oblongata on diffusion weighted and apparent diffusion coefficient imaging sequences. Early resumption of normal activity should be encouraged, to promote compensation. Cawthorne Cooksey exercises for vestibular rehabilitation therapy can further promote this process. A retrospective study on 148 patients by D. Huppert et al (Low recurrence rate of vestibular neuritis: A long-term follow-up. Neurology 2006; 67:1870–1871), the long-term recurrence rate of vestibular neuronitis for the entire follow-up period was 1.9% ( 2 out of 148 patients) and in both patients, the second occurrence of vestibular neuronitis affected the contralateral ear with respect to the initial manifestation. Thus, for all practical purposes, vestibular neuronitis is a monophasic illness.

What is Labyrinthitis?

Labyrinthitis, by definition, is a combination of the symptoms of vestibular neuritis, with the addition of hearing symptoms. It may be due to a disease that affects the inner ear as a whole or due to a disease that affects the 8th nerve as a whole. Labyrinthitis is also always attributed to an infection like meningitis (streptococcal, meningococcal, cryptococcal), mumps, rubeola, rubella, syphilis, herpesvirus (simplex, zoster, varicella), Lassa fever, HIV/AIDS, mononucleosis, mycoplasma, toxoplasmosis and cytomegalovirus. It is important to remember that blood to the inner ear is supplied by the internal auditory artery (IAA), which arises from the anterior inferior cerebellar artery (AICA). In the internal auditory canal, the IAA supplies the ganglion cells, nerves, dura and arachnoid membranes. It then divides into two main branches, the common cochlear artery and the anterior vestibular artery. The common cochlear artery further divides into the main cochlear artery and the vestibulocochlear artery, the latter forming the posterior vestibular artery and the cochlear ramus. The main cochlear artery supplies the apical three fourths of the cochlea, whereas the cochlear ramus irrigates the basal one fourth. The anterior vestibular artery supplies the utricle, superior part of the saccule, and ampullae of the anterior and horizontal semicircular canals. The posterior vestibular artery is the source of blood supply to the inferior part of the saccule and the ampulla of the posterior semicircular canal. The intraosseous branches (collaterals) of the vestibulocochlear artery and its vestibular branch are more abundant than those of the anterior vestibular artery (Mazzoni A. Internal auditory artery supply to the petrous bone. Ann Otol Rhinol Laryngol 1972; 81:13-21). The internal auditory artery (IAA) and its subdivisions are end arteries and are devoid of collaterals from other major arterial branches. Therefore, even brief periods of ischemia can cause inner ear damage causing an acute audiovestibular syndrome that is difficult to distinguish from acute labyrinthitis. Thromboses with vasospasm and artery-to-artery embolism are the two possible vascular mechanisms to explain isolated labyrinthine infarction.