Vestibular Neuritis

Clinic

• VN is the second most common cause of peripheral vestibular vertigo
• The first is Benign Paroxysmal Positional Vertigo
• It is a disorder thought to represent the vestibular-nerve equivalent of sudden sensorineural hearing loss.

Synonyms

• Synonyms for vestibular neuritis include
  • Acute labyrinthitis
  • Acute unilateral vestibular paralysis
  • Epidemic vertigo

Causes

• A sudden unilateral loss of vestibular function. In the majority of cases, the functions of the organs that are innervated by the superior vestibular nerve (the superior and lateral semicircular canals and the utricle) are damaged, but the functions of the organs that are innervated by the inferior vestibular nerve (the posterior semicircular canal and the saccule) are spared
• 30% of all affected patients had common colds prior to developing the disease.

Sign / Symptoms

• Sudden, severe, and prolonged vertigo measured over several days
• Absence of auditory symptoms (deafness or tinnitus)
• Absence of other neurological symptoms (particular diplopia or dysarthria).

DD

Meniere's disease

• It can almost always be excluded on the basis of the absence of hearing loss. In rare cases, hearing loss can be absent early in the course of Meniere's disease
• The vertigo of Meniere's disease is characteristically episodic and lasts a few hours, while the vertigo of vestibular neuronitis is usually constant and lasts several days.

MS

• Multiple sclerosis rarely presents as isolated vertigo, and it may be impossible to distinguish it from VN until further evidence of CNS involvement emerges.
• The differential diagnosis is difficult, and the final diagnosis is confirmed by neuroimaging

Peripheral labyrinthine

• Peripheral labyrinthine and vestibular nerve disorders that mimic vestibular neuritis includes several rare conditions.

Ramsay-Hunt syndrome

• Initial burning pain and blisters that occur with hearing disorders and facial paresis are typical for herpes zoster oticus
• Cogan syndrome is a severe autoimmune disease accompanied by interstitial keratitis and audiovestibular symptoms
• Vogt-Koyanagi-Harada syndrome is a rare multisystemic disease that affects tissues containing melanin, including the eye, inner ear, meninges, and skin
• Pseudoneuritis secondary to an ischemic stroke in the posterior fossa

Pathogenesis

It is a well established axiom of otolaryngology that when the inner ear is involved in disease, cochlear and vestibular elements are compromised, which leads to hearing loss and vertigo. In cases of vestibular neuronitis, vertigo occurs in the absence of hearing loss, the inner ear is not involved, and the lesion lies in the vestibular neurons central to the labyrinth.

The absence of brainstem involvement suggests that the lesion is limited to the vestibular nerve. It is helpful to think of vestibular neuronitis as being a mononeuropathy, although this finding has not been confirmed. Whether the disease is caused by direct infection, localised thrombosis, or an autoimmune reaction remains unclear.

Infectious causes

Viral upper respiratory tract infections, particularly those caused by influenza virus A, influenza virus B, and adenoviruses, as well as infections caused by herpes simplex virus, cytomegalovirus, Epstein-Barr virus, rubella virus, and parainfluenza virus [30, 31]. Despite clear serological evidence of a recent viral infection, no virus has been isolated from the blood, respiratory tract, or cerebrospinal fluid of patients, despite repeat attempts [31].

The histopathology of the vestibular nerve in cases of vestibular neuritis has exhibited atrophy of the vestibular nerve and the vestibular sensory epithelium. These results are similar to the histopathological findings in known viral disorders, such as herpes zoster oticus [26]. Herpes simplex virus type 1 (HSV-1) DNA has been detected at the time of autopsy with the use of the polymerase chain reaction in human vestibular ganglia [32] (Figure 2).

Figure 2

(A) schematic drawing of vestibular and facial nerves. Different section of vestibular ganglion (a) sterm, (b) inferior portion, and (c) superior portion. (B) Longitudinal section of human vestibular ganglion (a) sterm, (b) inferior portion, and (c) superior portion. Using polymerase chain reaction, herpes simplex virus 1 (HSV-1) DNA was found in 60% of the human esamine ganglia (from Arbusow et al.).

An animal model of vestibular neuritis was developed by inoculating HSV-1 into the auricle of mice [33]. In animals, vestibular symptomatology can also be induced by the intralabyrinthine inoculation of a variety of viral strains [34, 35]. In these types of experiments, the presence of viral antigens has been identified within the vestibular membranous labyrinth and Scarpa's ganglion cells [36]. Evidence for a viral infection in vestibular neuritis in humans is less convincing.

There are many similarities between VN and Bell palsy, and the reactivation of neurotropic viruses, including herpes simplex virus type 1, has been suggested as the cause of both conditions. Herpes simplex virus type 1 DNA is detected by polymerase chain reaction in approximately two-thirds of human vestibular and facial ganglia [32–37].

If HSV-1 is the most likely cause of VN, the virus would reside in a latent state in the vestibular ganglia. The virus could be located in the ganglionic nuclei, as has been reported in other cranial nerves [38, 39]. Other biological factors allow the virus to suddenly replicate, inducing inflammation and edema. This process causes secondary cell damage of the vestibular ganglion cells and axons in the bony canals.

Although the most popular theory of the pathogenesis of vestibular neuritis is based on a viral infection, the evidence to support this hypothesis remains circumstantial [40, 41].