Vestibular Neuritis and Labyrinthitis

Timothy C. Hain, MD   • Page last modified: July 23, 2022

Whats new ?

  1. There recently has been a spike in Vestibular Neuritis in Chicago (as of 7/2022). This may be due to covid-19.
  2. New technology has greatly enhanced our ability to detect vestibular neuritis. The VHIT test is both accurate and very quick, as well as unlikely to make a person dizzier than they already are. We offer this technology in our clinic in Chicago.

Introduction:

Below is a movie of Vestibular Neuritis

In vestibular neuritis, also known as vestibular neuronitis, dizziness is attributed to a viral infection of the vestibular nerve or ganglion (see figure 1). The vestibular nerve carries information from the inner ear about head movement. When one of the two vestibular nerves is infected, there is an imbalance between the two sides, and vertigo appears. Vestibular neuronitis is another term that is used for the same clinical syndrome, and reflects the idea that the damage is often to the vestibular ganglion which contains neurons rather than the vestibular nerve itself.

The various terms for the same clinical syndrome probably reflect our lack of ability to localize the site of lesion. The term "neuritis" implies damage to the nerve, and "neuronitis', damage to the sensory neurons of the vestibular ganglion. There is actually evidence for both. There is also some evidence for viral damage to the brainstem vestibular nucleus (Arbusow et al, 2000), a second potential "neuronitis". As the vestibular neurons are distinct from cochlear neurons in the brainstem, this localization (as well as the vestibular ganglion) makes more sense than the nerve in persons with no hearing symptoms. Nevertheless, if the nerve were involved after it separates from the cochlear nerve, neuritis would still be a reasonable mechanism. Prior to death and autopsy there is no way to make a clear distinction, and the present favored term is "neuritis".

Labyrinthitis, is defined as the combination of the symptoms of vestibular neuritis, with the addition of hearing symptoms. It may be due to a process that affects the inner ear as a whole or the 8th nerve as a whole. Labyrinthitis is also always attributed to an infection.

Figure 1: Cutaway of the inner ear. Movement of the head is detected by the semicircular canals, and transmitted to the brain via the vestibular nerve. Vestibular neuritis may affect the nerve itself or the vestibular ganglion (Scarpa's ganglion).

In vestibular neuritis, the virus that causes the infection is thought to be usually a member of the herpes family, the same group that causes cold sores in the mouth as well as a variety of other disorders (Arbusow et al, 2000). There is some controversy about this idea however, as there is little direct evidence for herpes infection (Matsuo, 1986). Slightly more evidence was provided by Rujescu et al (2020) who noted that vestibular neuritis is associated with a gene suggesting risk for herpes. The varacella zoster virus (the cause of Ramsey Hunt) is also thought to be a common source of vestibular neuritis. There may also be some cases associated with the covid-19 virus.

It is also thought that a similar syndrome indistinguishable from vestibular neuritis can be caused by loss of blood flow to the vestibular system (Fischer, 1967). However, present thought is that inflammation, presumably viral, is much more common than loss of blood flow. Also against this idea is that the blood supply to the inner ear largely comes from the labyrinthine artery, which supplies both hearing and vestibular. Thus, it should be very unlikely to have a purely vestibular syndrome as a vascular event. There are still some that disagree (Fattori et al. 2003) .

In labyrinthitis, it is thought that generally viruses cause the infection, but rarely labyrinthitis can be the result of a bacterial middle ear infection. While there are several different definitions of vestibular neuritis in the literature, with variable amounts of vertigo and hearing symptoms, we will use the definition of Silvoniemi (1988) who stated that the syndrome of vestibular neuritis is confined to the vestibular system. In vestibular neuritis, by definition, hearing is unaffected. In labyrinthitis, hearing may be reduced or distorted in tandem with vertigo.

These definitions are flawed -- they depend on clinical findings and imply anatomic localization that may not always be true. It has been reported that some patients with the clinical syndrome of "vestibular neuritis", anatomically may have lesions in the labyrinth (Murofushi et al, 2003). Although anatomic data is rarely available, if diagnostic technology improves in the future, we may need to change the definition of "vestibular neuritis".

Both vestibular neuritis and labyrinthitis are rarely painful -- when there is pain it is particularly important to get treatment rapidly as there may be a treatable bacterial infection or herpes infection.

The symptoms of both vestibular neuritis and labyrinthitis typically include dizziness or vertigo, disequilibrium or imbalance, and nausea. Acutely, the dizziness is constant. After a few days, symptoms are often only precipitated by sudden movements. A sudden turn of the head is the most common "problem" motion. While patients with these disorders can be sensitive to head position, it is generally not related to the side of the head which is down (as in BPPV), but rather just whether the patient is lying down or sitting up.

Pathologic study of a single patient documented findings compatible with an isolated viral infection of Scarpa's ganglion (the vestibular ganglion). There was loss of hair cells, "epithelialization" of the utricular maculae and semicircular canal cristae on the deafferented side, and reduced synaptic density in the ipsilateral vestibular nucleus (Baloh et al, 1996).

VEMP VHIT

Absent oVEMP (superior division), Courtesy of Dr. Dario Yacovino.

Absent left anterior and lateral canal response on VHIT, Courtesy of Dr. Dario Yacovino.

In spite of the limited pathology that would suggest involvement of the entire vestibular nerve, there is reasonable evidence that vestibular neuritis often spares part of the vestibular nerve, the inferior-division (e.g. Fetter and Dichgans, 1996; Goebel et al, 2001) although not all agree (Lu et al, 2003). It would be hard to see how a "neuronitis" could select just one part of the vestibular nerve. So if one gets down to the details, one might have to split the syndrome up into diffuse "neuronitis", and more focal "neuritis".

Because the inferior division supplies the posterior semicircular canal and saccule, even a "complete" loss on vestibular testing (associated with a superior canal lesion) may be associated with some retained canal function. Furthermore, it is common to have another dizziness syndrome, BPPV, follow vestibular neuritis. Presumably this happens because the utricle is damaged (supplied by the superior vestibular nerve), and deposits loose otoconia into the preserved posterior canal (supplied by the inferior vestibular nerve). The combination of vestibular neuritis and BPPV is sometimes called Lindsay-Hemenway syndrome.

Similarly, an inferior division vestibular neuritis might be associated with a normal ENG test but an abnormal cVEMP test. (Aw et al, 2001). Practically speaking, we are not sure that this is a real entity as abnormal VEMPs are common in otherwise normal persons. While the VHIT test can theoretically measure inferior division vestibular neuritis, we are not sure right now that this is very accurate. That being said, we have no doubts about VHIT diagnosing the common superior division vestibular neuritis, or injuries to the entire nerve or ganglion as it may be..

How Common is Vestibular Neuritis ?

Estimate of prevalence from VHIT testing
Fraction of VHIT tests with unilateral deficits, between 2016 and 2022 at Chicago Dizziness and Hearing.

 

About 5% of vertigo is due to vestibular neuritis or labyrinthitis. The figure above shows data from our clinic where new dizzy patients are tested with VHIT tests, and document roughly a 5% frequency of abnormal VHIT tests over most of the years of monitoring. This is based on many thousands of VHIT tests. Vestibular neuritis occurs in all age groups, but cases are rare in children. Brodsky et al (2016) reported 11 patients out of 301 evaluated at their pediatric vestibular clinic. (Brodsky et al, 2016).

In the author's clinical practice, Chicago Dizziness and Hearing, as of 2016 there were more than 700 patients with this diagnosis out of roughly 20,000 total patients. This fraction is far less than patients with Migraine, but comparable to patients with Meniere's disease. If there is a 5% prevalence, one would expect 1000 patients -- not too far off.

How is the diagnosis of Vestibular Neuritis and Labyrinthitis made?

Acutely, in uncomplicated cases, a thorough examination including video-frenzel goggles is all that is necessary. The VHIT test is particularly good for diagnosis as it is very efficient in detecting vestibular neuritis and is generally normal in strokes. Certain types of specialists, "otologists", "neurotologist", and "otoneurologists", are especially good at making these diagnoses and seeing one of these doctors early on may make it possible to avoid unnecessary testing, as well as inappropriate treatment or medication. In large part, the process involves ascertaining that the entire situation can be explained by a lesion in one or the other vestibular nerve. It is not possible on clinical examination to be absolutely certain that the picture of "vestibular neuritis" is not actually caused by a brainstem stroke, or cerebellar stroke, or an inner ear tumor, so mistakes are possible (Lee et al, 2003). A positive VHIT test helps considerably by (usually) crossing strokes off the list of possibilities. Because of the better technology and also because strokes and tumors happen so rarely that it is not necessary to perform MRI scans or the like very often for this situation.

In severe or complex situations, we will sometimes (not always) order the following tests:

An example of an acutely positive Rotatory chair:

Acute Vestibular Neuritis

There is reduced gain at low frequencies, increased phase, a very strong asymmetry (from the spontaneous nystagmus). The gain-TC product here was 2.6, which suggests unilateral loss.

VN spontaneous

The recording here shows very powerful right-beating spontaneous nystagmus, associated with left vestibular neuritis.

After a week goes by, the spontaneous nystagmus abates but the gain/phase remain abnormal.

Stronger nystagmus with bad ear up

As first described by Fluur (1973), on positional testing, the horizontal nystagmus is usually strongest with the "bad" ear down, and weakest with the "good ear up". This is called "homolateral excitation". This is shown above using the head-prone test. This individual has strong left vestibular neuritis, with right-beating nystagmus. It is more powerful with the head-right (putting the left ear down), than head-left. This particular person's torsional nystagmus was more obvious with the right ear down. Wang et al (2021) reported similarly that "SPV in AED had a median value of 7.8°/s, which was greater than when supine (P = 0.008) and HED (4.8°/s) (P < 0.001)." They used "AED" to be "affected ear down", and "HED" to be "healthy ear down", so this works out to the same observation as Fluur.

Example of positive VENG

Caloric test in vestibular neuritis

This caloric test was done 1 month after acute onset of vestibular neuritis. The left ear is normal, the right shows no response. Ice water and prone made no difference.

oVEMP test in vestibular neuritis.

oVEMP test in vestibular neuritis

There is normal oVEMP on the (good) left ear, and no oVEMP on the right side.

Differential diagnosis (common considerations)

The VHIT test has immensely simplified the differential diagnosis of Vestibular Neuritis. VN is mainly diagnosed with security when there is a strong unilateral positive on the VHIT, and symptoms that last longer than a few days. The VHIT is not yet universally available, but its adoption seems to be rapid in the USA. The office "HIT" test is nearly as good, as long as the person doing the test is highly experienced. However, we prefer the paper trail of the VHIT to the more subjective nature of the HIT.

There are many medical conditions that can create roughly the same constellation of findings and symptoms as vestibular neuritis and labyrinthitis. Sorting these out usually is done by a physician who can combine clinical knowledge and experience with results of inner ear testing. A "classic" case of VN mainly relies on ascertaining that findings consist of a subacute onset (over hours but usually lasting days) of pure dizziness.