A few things that have been learned:
- The ototoxic drug destroys the vestibular hair cells (the neural sensory
cells) before (at lower doses) it destroys the auditory hair cells. With
carefully controlled doses spaced over days or administered continuously
over days or weeks, damage to the hearing function can be almost totally
avoided and damage to the vestibular hair cells can be stopped as soon
as vertigo is controlled.
- As is the case with many instances in neurosurgery, the staged application
of the drug over a long period while the patient remains active appears
to allow the central nervous system to "recalibrate" fairly well
and avoid significant balance problems or visual fixation/stabilixzation
problems. The alternative--surgery--cannot provide this important advantage.
In fact, many patients who have severe Meniere's and end up having both
vestibular systems destroyed or disconnected by surgery end up fully disabled.
With current methods of bilateral ototoxic vestibular ablation the patient
is able to move around essentially normally.
- It has been documented in the past few years, that the gentamicin also
destroys or changes part of the "dark cells" in the inner ear.
These cells appear to be responsible for control of ionic balances within
the inner ear and the production of endolymph. In Meniere's disease, the
dark cells are suspect. They may be the root cause of at least some cases.
Gentamicin has been shown to reduce production of endolymph in healthy
guinea pigs. Whether gentamicin can reduce the endolymphatic hydrops that
is believed to be responsible for the symptoms and progression of Meniere's
is not yet known, but data showing hearing preservation show that it may
work that way in some cases.
- There is evidence that gentamicin in low doses can preserve
hearing. Not all studies show this result and researchers are trying to
determine how the different treatments/protocols vary in this regard. Some
large studies have shown hearing stabilization of over 90%, others have
shown no hearing stabilization at all. The assumption is that gentamicin
selectively destroys the endolymph-production capacity of the inner ear,
resulting in better ionic (salt) balance in the fluid and lowered pressure.
Let me add that the most ototoxic thing in Meniere's disease is the
endolymph that is overproduced in part of the cochlea. This fluid appears
to leak and enter the perilymph and contact both vestibular and auditory
hair cells which it then poisons. Introduction of the right amount of the
"ototoxic" gentamicin can--maybe--stop this natural ototoxic
process.
Thanks to Jim Chinnis for this explanation.
Send comments and suggestions to: [email protected]
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