вторник, 22 януари 2008 г.

Vestibular Neuritis and Labyrinthitis.

In vestibular neuritis, dizziness is attributed to a viral infection of the vestibular nerve (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. 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 due to a process that affects 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). 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. 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. Recently evidence has been put forth 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). 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) as well as spare the superior division (Aw et al, 2001) although not all agree (Lu et al, 2003). 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. Similarly, an inferior division vestibular neuritis might be associated with a normal ENG test but an abnormal VEMP test. 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).
How Common is Vestibular Neuritis ?
About 5% of all dizziness (and perhaps 15% of all vertigo) is due to vestibular neuritis or labyrinthitis. It occurs in all age groups, but cases are rare in children.
How is the diagnosis of Vestibular Neuritis made?
Acutely, in uncomplicated cases, while a thorough examination is necessary, no additional testing is usually required. 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 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 or cerebellar stroke, so mistakes are possible (Lee et al, 2003). Nevertheless, this happens so rarely that it is not necessary to perform MRI scans or the like very often.
Movie of nystagmus of vestibular neuritis.
Signs of vestibular neuritis include spontaneous nystagmus, and unsteadiness. One may notice that vision is disturbed or jumpy on looking to a particular side. This usually means that the opposite ear is affected -- it is called "Alexander's Law" and is due to asymmetric gaze evoked nystagmus. Occasionally other ocular disturbances will occur such as vertical double vision -- skew deviation (Safran et al, 1994).
However if symptoms persist beyond one month, reoccur periodically, or evolve with time (see following), testing may be proposed. In this situation, nearly all patients will be asked to undergo an audiogram and an ENG. An audiogram is a hearing test needed to distinguish between vestibular neuritis and other possible diagnoses such as Meniere's disease and Migraine. The ENG test is essential to document the characteristic reduced responses to motion of one ear. An example of this is shown on the caloric test page.
An emerging test called a VEMP may be helpful in determing the extent of damage (Lu et al, 2003). Also, VEMP can be helpful in confirming the diagnosis of vestibular neuritis as opposed to another process that has damaged the nerve as most persons with vestibular neuritis will have reduced ENG function but a present (abeit perhaps reduced) VEMP.
An MRI scan will be performed if there is any reasonable possibility of a stroke or brain tumor. As illustrated in the cases here, sometimes these can be very difficult to detect at the bedside. Occasionally with an MRI one can visualize the inflammation of the vestibular nerve. In most instances, it is most cost effective to see a neurologist prior to obtaining an MRI. Blood tests for diabetes, thyroid disorders, Lyme disease, collagen vascular disease and syphilis are sometimes performed, looking for these treatable illnesses. However, it is rare that these are ever positive.
See this page for all of the tests done on an example patient with vestibular neuritis.
See this page for all of the tests done on an example patient with labyrinthitis.
How is Vestibular Neuritis and Labyrinthitis Treated?
Acutely, vestibular neuritis is usually treated symptomatically, meaning that medications are given for nausea (anti-emetics) and to reduce dizziness (vestibular suppressants). Typical medications used are "Antivert (meclizine)", "Ativan (lorazepam) ", "Phenergan", "Compazine", and "Valium (diazepam) ". When a herpes virus infection is strongly suspected, a medication called "Acyclovir" or a relative may be used.
Steroids (prednisone, methylprednisolone or decadron) are also used for some cases. Strupp and others (2004) recently reported that steroids (methylprednisolone for 3 weeks) significantly improved the recovery of peripheral vestibular function in patients with vestibular neuritis, while valacyclovir did not. All patients were also given an anticholinergic medication (pirenzepine). Side effects were encountered including a gastric ulcer in one patient and induction of diabetes in two others. Strupp and coauthors did not indicate a mechanism for the positive effect of steroids. If real, the effect may be via reduction of nerve swelling.
Acute labyrinthitis is treated with the same medications as as vestibular neuritis, plus an antibiotic such as amoxicillin if there is evidence for a middle ear infection (otitis media), such as ear pain and an abnormal ear examination suggesting fluid, redness or pus behind the ear drum. Occasionally, especially for persons whose nausea and vomiting cannot be controlled, an admission to the hospital is made to treat dehydration with intravenous fluids. Generally admission is brief, just long enough to rehydrate the patient and start them on an effective medication to prevent vomiting.
It usually takes 3 weeks to recover from vestibular neuritis or labyrinthitis. Recovery happens due to a combination of the body fighting off the infection, and the brain getting used to the vestibular imbalance (compensation). Some persons experience persistent vertigo or discomfort on head motion even after 3 weeks have gone by. After three months, testing (i.e. an ENG, audiogram, VEMP, and others) is indicated to be certain that this is indeed the correct diagnosis and a referral to a vestibular rehabilitation program, may help speed full recovery via compensation.
How might vestibular neuritis affect my life ?
You will probably be unable to work for one or two weeks. You may be left with some minor sensitivity to head motion which will persist for several years, and may reduce your ability to perform athletic activities such as racquetball, volleyball and similar activities. After the acute phase is over, for a moderate deficit, falls are no more likely than in persons of your age without vestibular deficit (Herdman et al, 2000). Persons in certain occupations, such as pilots, may have a greater long term impact (Shupak et al, 2003).
You may also have mild problems with your thinking. Even in persons who are well compensated, sensory integration seems to require more attention in persons with vestibular lesions than normal subjects (Redfern et al, 2003).
Recurrent vestibular neuritis -- Benign recurrent vertigo
Fortunately, in the great majority of cases (at least 95%) vestibular neuritis it is a one-time experience. Rarely the syndrome is recurrent, coming back year after year. When it is recurrent, the symptom complex often goes under other names. These include benign paroxysmal vertigo in children (Basser, 1964), benign recurrent vertigo (Slater 1979, Moretti et al, 1980), or vestibular Meniere's syndrome (Rassekh and Harker, 1992). Many authors attribute this syndrome to migraine associated vertigo. There is often a familial pattern (Oh et al, 2001)
When labyrinthitis recurs, the diagnosis is often changed from labyrinthitis to "Meniere's disease". The reason for this is that the diagnostic criteria for Meniere's are essentially those of recurrent labyrinthitis. It is the author's impression that this "conversion" process occurs far more commonly than there is recurrent vestibular neuritis.
Quick spins
Another recurrence pattern in vestibular neuritis is the "quick spin" pattern - -people complain of brief spells lasting seconds to minutes in which the entire world rotates at high speed, then stops, without any hearing symptoms. This may occur as often as 50 times/day. This pattern of dizziness often responds to anticonvulsants such as carbamazepine or oxcarbamazine. In this disorder, one can often recognize the patient the video-frenzel goggles. There is a paretic type spontaneous nystagmus and vibration induced nystagmus, which reverses with hyperventilation for 30 seconds.
Case example of quick spins: A middle aged administrator complained of multiple spells of spinning vertigo with nausea unaccompanied by hearing symptoms. The spells lasted 10-20 minutes, were accompanied by sweating and nausea. He has had times in which he has had three or four episodes per day. There appear to be no consistent triggers. On examination, a right-beating spontaneous nystagmus was observed. This reversed direction with hyperventilation. Hearing testing was normal as was ENG testing and MRI scan. After being started on oxcarbamazine, gradually increasing to 600 mg twice/day, his spells decreased to less than once/two weeks, and were minimal in intensity.
Acknowledgment: The graphic of figure 1 is courtesy of Northwestern University and was originally funded by NIH.
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