Timothy C. Hain, MD Page last modified: July 17, 2011
This page mainly describes a clinical syndrome caused by irritibility of the vestibular nerve. The main clinical feature is repeated brief spells of vertigo, variably accompanied by other signs of damage to the 8th nerve. The best name for this syndrome is probably "vestibular paroxysmia".
There are several processes that have been suggested by ourselves and others to cause "vestibular paroxysmia"
|Microvacular compression due to left intra-IAC loop with vestibular paroxysmia (image due to Dr. Dario Yacovino).|
The most well known of these is microvascular compression.In microvascular compression syndrome (MVC), vertigo and motion intolerance is attributed to irritation of the vestibular portion of the 8th cranial nerve by a blood vessel. It is a controversial syndrome at present, but in the author's opinion, there is some validity to it. The characteristic symptom of nerve irritation is quite common in clinical practice, and it does usually respond to medication. The controversial part is the origin. If one accepts that these symptoms are always due to blood vessels, than a surgical approach is worth considering. On the other hand, if these symptoms are generally due to other processes, then medical management should be preferred. It is the opinion of the author of this page, that the latter is the case.
The existence of MVC was inferred by analogy to the syndrome of hemifacial spasm, in which it is well accepted that the usual cause is a aberrant blood vessel. Dr. Peter Jannetta, a neurosurgeon in Pittsburgh Pennsylvania, together with Drs Aage Moller and Margarita Moller, pioneered the diagnosis and treatment of this condition. Although hemifacial spasm is now presently well accepted to be related to vascular compression, the numerous other syndromes proposed by Janetta and associates to be related to vascular compression (e.g. trigeminal neuralgia, glossopharyngeal neuralgia, and even essential hypertension) are not as well accepted as being a consequence of vascular compression.
In 1984, Janetta, MB Moller and AR Moller described "Disabling positional vertigo", characterized by a history of vertigo, a small midfrequency notch on audiometry, acoustic reflex abnormalities, and an increased I-III latency with brainstem audio-evoked responses using a "tone burst" stimulus. The "positional vertigo" designation appears to be a misnomer as subsequent authors have not emphasized this finding. Some have indicated that motion intolerance may include repositioning. Jannetta and associates proposed treatment by placing an absorbable sponge between the nerve and the blood vessel. While this treatment is intended to buffer the nerve from the blood vessel, later writers have questioned whether this procedure actually simply damages the 8th nerve, or that it is actually a sham procedure (Schalber and Hall, 1992). Others have suggested that the appropriate treatment is vestibular nerve section (McCabe and Harker, 1983).
|Authors||Subjects||Vertigo or disequilibrium||Hearing loss||Motion Intolerance||Other Symptoms|
|Brookler and Hoffman, 1979||5||5||5||Caloric weakness in 4/5|
|Applebaum and Valvasori,1984 and 1985||10||No caloric weakness, spontaneous nystagmus|
|McCabe and Harker, 1983||8||Brief spells of vertigo 2-3 min||Main symptom||Spontaneous nystagmus|
|Wiet, 1989||6||Yes||Yes||Yes||Air contrast CT|
|McCabe and Gantz, 1989||34||Brief spells||Yes||
Failure of medical management
Air contrast CT
|Ter Bruggen, et al, 1987||10||spells||ABR abnormalities|
|Meyerhoff and Mickey, 1998||2||Yes||Tinnitus, normal MRI|
|Moller, 1990||41||Yes||ABR, I-III latency|
|Ryu et al, 1988||27||Seconds to minutes||20/27||
Tinnitus, decreased calorics
Air contrast CT, ABR not helpful
|Kanzaki and Koyama, 1986||2||Yes||Yes||
Air contrast CT helpful
|Brackmann et al, 2001||20||Triggered by supine->sitting||5%||Yes||Positive air-contrast CT or MRI, ABR not helpful|
|Huffner et al, 2008||32||Brief attacks||50%||At rest||ENG, HV induced nystagmus, CISS MRI 95%|
In spite of numerous papers being published on this condition, the very existence of MVC continues to be questioned. The symptoms of MVC are all nonspecific ones, that could easily be found in other conditions such as Meniere's disease, Migraine or simply a constitutional motion intolerance. No specific convincing test abnormality has yet been demonstrated. The ABR findings reported by Moller to be characteristic of MVC would not be considered abnormal by most clinicians (Schwaber and Hall, 1992). No findings related to blood vessels (e.g. air CT, MRA, etc.) will ever be diagnostic as blood vessels cross the 8th nerve of at least a third of normal individuals (Parnes, 1990).
A specific type of tinnitus called "typewriter tinnitus" has been suggested to be due to microvascular compression of the cochlear nerve (Levine, 2006). See here for more detail.
In essence then, MVC is a syndrome of vestibular (quick spins, possibly combined with motion intolerance) or positional auditory symptoms that respond to treatment with medications for neuralgia (e.g. carbamazepine or oxcarbamazine), and in which other reasonable causes (i.e. Meniere's disease, Migraine, labyrinthitis, fistula) have been excluded.
Logically, there is nothing about this constellation of symptoms that requires a vascular origin. The key features of the syndrome boil down to what should describe an electrical problem - -very brief and strong symptoms, that respond to neuralgia medications. Anything that irritates the vestibular nerve or central vestibular pathways, should cause similar symptoms, and the literature says that it does (e.g. Moon and Hain, 2005).
Thus a more reasonable name for this syndrome is vestibular paroxysmia. See the above table for a list of possible causes.
"Quick spins" and acquired motion intolerance may be characteristic clinical symptoms, although at the present writing, studies looking for subpopulations with those particular index symptoms for response to decompression surgery have not been made (and probably they will never be done). In our opinion, air contrast CT or MRI/MRA are not diagnostic if a blood vessel is seen, it need not be viewed with concern, but MRI/MRA may help in excluding alternative causes. Newer types of MRI including FT-FISS may be more helpful .
McDermott and associates, in a large study, recently reported that loops that extend into the IAC (internal acoustic canal) are more significant sources of unilateral auditory symptoms (such as tinnitus) than loops simply within the CPA (cerebellopontine angle). (McDermott et al, 2003). A simple severity classification system from McDermott et al (2003) is as follows: type I -- in the CPA but not entering the IAC, type II, entering the IAC but extending less than 50% of the length of the IAC, and type III, extending more than 50% of the length of the IAC. Gultekin and associates reported no correlation (2008).
CISS MRI was reported "positive" in 95% of the patients reported by Huffner et al (2008). As there are blood vessels in everyone's IAC , and there are certainly many other potential causes of vestibular nerve irritibility, in our opinion, this finding is difficult to interpret.
ABR, if abnormal on the side of auditory symptoms supports the diagnosis, but a normal ABR does not exclude it. Quality control on ABR testing is terrible, and norms are often unavailable even in textbooks as they are device specific. Furthermore, ABR peak assignment is generally very haphazard and without any consideration of noise. For this reason we do not generally recommend using ABR for diagnosis of MVC.
In essence, this syndrome cannot be definitively diagnosed until a surgical exploration has been done and the patient is cured on follow-up. Our feeling, however, is that this is an unreasonably agressive approach to diagnosis, and that the combination of the studies below and hyperventilation induced nystagmus that reverses the spontaneous nystagmus is sufficient to diagnose.
A recent uncontrolled study of Hufner et al (2008) is heavily quoted below. Because this study was uncontrolled, one should be cautious in interpreting these numbers as we don't know how many people "on the street" might have exactly the same findings.
At any rate, the present author suggests the following set of tests for an individual in whom the diagnosis of microvascular compression is contemplated:
On physical examination, the combination of finding a spontaneous nystagmus that reverses on hyperventilation is (in our opinion anyway), highly suggestive of vestibular paroxysmia and response to treatment (see below). This observation has recently been corroberated by Huffner et al (2008).
|The way that I test for hyperventilation induced nystagmus in my dizzy clinic. There is also a MOVIE: hvt small.avi (15 meg) Hyperventilation induced nystagmus in person with an irritible vestibular nerve due to a left sided acoustic neuroma. This is a rather long (1.5 minute) clip.|
It is the author's view that a trial of treatment with oxcarbamazine (an anticonvulsant that is a sodium channel blocker) is usually indicated for the index symptom of "quick spins". This was also the suggestion of Hufner et al (2008). Addition of baclofen may be reasonable if there is a partial response. Other treatments of neuralgia, such as other anticonvulsants (carbamazepine) may also be considered. We have had some success with Keppra. (levetiracetam)
We advise extreme caution. Logically, only treatments that affect the nerve proximal to the site of irritation seem likely to work. In other words, transtympanic gentamicin treatment and a simple labyrinthectomy seem unlikely to be effective. Vestibular nerve section seems overly aggressive in as much as the diagnosis is so difficult and the disability of nerve section is relatively high.
The decompression surgery (e.g. Brackmann et al, 2001 as well as multiple authors in the table above) is risky as it involves a neurosurgical approach to the brainstem area. Because the diagnostic criteria at the moment require response to medication, surgery seems reasonable only as a last resort in individuals who develop medication intolerance, and in whom all other reasonable alternatives have been excluded.
|© Copyright April 6, 2012 , Timothy C. Hain, M.D. All rights reserved. Last saved on April 6, 2012|