Sedating the Auditory Nerve

[Sjoerd]

Hallo Dr Nagler,

There seems to be an ongoing debate of tinnitus could be originating from the inner ear. In the past (in some cases) the Auditory nerve was severed and the tinnitus would resolve, or it would not. In the sort mailing I had with a dutch tinnitus researcher he said: the success rate of this type of intervention is highly exaggerated. If it would be successful, section of the nerve will cause new tinnitus to arrive. It seems difficult to completely rule out tinnitus with an inner ear "source/driver".

My question is: Why is it not possible to sedate the auditory nerve and find out that way. Is it dangerous? Is it difficult? etc etc.

Kind Regards,
Sjoerd

 

[Dr. Nagler]

My question is: Why is it not possible to sedate the auditory nerve and find out that way. Is it dangerous? Is it difficult? etc etc.

It's an interesting question, Sjoerd. I guess in theory you could temporarily block impulses from propagating along the auditory nerve with some sort of local anesthetic. But the problem is (1) how to get to it technically and (2) once there how to block it safely. I'll ask a few otologists and neurosurgeons over the next couple of weeks. If I come up with something, I'll revise my response and add some details.

Dr. Stephen Nagler

 

[Dr. Nagler]

Hi @Sjoerd -

Back again after a few months ...

I have now posed your interesting question to a number of ENTs and otologists.

So here's the deal.

Years and years ago a handful of ENT surgeons did indeed offer auditory nerve section to very highly selected patients with severe intractable tinnitus, but the results were unpredictable and generally abysmal, largely because the resultant deafness (even if unilateral) prevented masking of any sort if the operation failed to relieve the tinnitus, which was unfortunately usually the case.

The idea of blocking the auditory nerve with a local anesthetic to determine which few patients might actually benefit from subsequently sectioning the nerve is intriguing. The problems with doing so are as follows:

The only way to get to the nerve would be via a craniotomy (i.e., through a hole in the skull such as done in acoustic neuroma surgery). You cannot approach it through the ear.

The patient would have to be awake during the procedure - because you would not want to use a long-acting anesthetic and risk permanent vestibular damage. (The vestibular nerve accompanies the auditory nerve and is more sensitive to anesthetics, ototoxic antibiotics, etc.)

And every ENT/otologist I talked to said that even if the test were positive, he would refuse to do the procedure because while permanent intractable tinnitus can be managed with TRT and the like, once you are deaf there is no going back.

So it sounds like the idea was elegant in conception, but is a non-starter in the laboratory of life.

Hope this helps. Sorry it took me so long to track down an answer.

Dr. Stephen Nagler