Timothy C. Hain, MD Page last modified: March 6, 2021
Additional Disclaimer: This material is not written for legal use, including trial testimony.
Bilateral Vestibular neuritis is a subtype of Bilateral Vestibular Loss. Bilateral Vestibular Loss is a rare condition - -Ward reported that it affects about 28/100,000, but this number doesn't seem to us to be very reliable. This suggests that bilateral vestibular neuritis must be even rarer. At Chicago Dizziness and Hearing, we have seen many patients with bilateral vestibulopathy, over about 30 years. The figure below shows data from a 176 patient subset of our entire database compiled in 2014. This data is being actively updated and does not include all of our patients, as this is a big project. These are all patients referred for clinical diagnosis. It does not include patients referred through medicolegal review activity.
As can easily be seen, the majority of cases are "idiopathic", and the second largest group are aminoglycoside ototoxicity (i.e. gentamicin+tobramycin+streptomycin).
If a virus can affect one vestibular nerve, why not the other ? There is a fairly well recognized situation where there is vestibular neuritis on one side, and then after a fairly long gap (usually years), on the other as well, leaving the person with both ears damaged. This was first described by Schuknecht and Witt in 1985. Here the diagnosis can be reasonably well established by observing two fairly common bouts of VN, but ending up with bilateral loss rather than recovery. As vestibular neuritis tends to spare the inferior vestibular nerve, one might expect these patients to have present "cVEMP" tests, but absent calorics and rotatory chair responses. The VHIT test provides another way to document this -- absent superior vestibular nerve responses (i.e. absent anterior canal and lateral canal), with preserved inferior vestibular nerve (i.e. Posterior canal). These situations are very unusual.
Medical Hypothesis -- the main source for "idiopathic" bilateral vestibular loss is simultaneous vestibular neuritis:
Perhaps the large group of "idiopathic" patients on the figure above are actually patients with bilateral vestibular neuritis. Vestibular neuritis, the unilateral variant, is far more common than bilateral vestibular loss, and it is plausible that should about 5% of VN actually be bilateral, it might entirely account for the "idiopathic" group above.
The situation where both ears are "taken out" at the same time, is plausible in this regard, but difficult to prove. There are indeed a very substantial number of "idiopathic" bilateral vestibular loss. However, as the causal diagnosis presumably would require an autopsy, it does not seem likely that we will clear this up anytime soon. This is a "medical hypothesis". Again, VHIT testing or the combination of a lateral canal test (calorics or R-chair) with a VEMP, might be a way to make this inference. One would expect that those with preserved portions of their vestibular system would do better, long term, than those with a total "wipe out". So there is some rehab implication.