Thankfully my neurologist HAS heard of this, and I did a lot of reading, as I too suffer from this.

It's thought (by 2 neurologists I consulted) that it's due to lesions/damage in the brain stem. - In my case.

If it's permanent or not, I'm not sure.. I've read reports that it can disappear after 7 years (approx), but I don't know, where combined with MS, if this may be a lasting, permanent thing.

BMS (If I used this term) is Burning Mouth Syndrome as was pointed out back when this thread was newer. It's horrible, and I've had it since 2007.

What works? Low dose Clonazepam (Klonopin) for me. I tried the Neurontin route, the side effects from Neurontin were dreadful and it did nothing to help the mouth. I tried low dose anti depressants (Amitriptyline mostly) and that didn't do a thing, again... terrible side effects.

What I find works:

1. Keeping stress levels/anxiety LOW (meditation, gardening, whatever you can do to calm yourself)
2. Getting 8 hours of sleep (at least) a night
3. Chewing gum (I love Stride sweet peppermint personally.. and the flavour lasts a long time)
4. Drinking lots of water
5. Eating a healthy, balanced diet
6. Being active (anything to keep your mind off the mouth!)
7. Medication (for me it's been Clonazepam, not a first 'choice' but if you've ruled out the other meds without success, I recommend asking your neuro or GP about it)

Hope this helps, and I hope you're able to find some relief. I've also read that swishing with tabasco sauce diluted in water CAN train your 'wiring' in the brain etc to recognize what a 'true hot' sensation is. I would imagine one could also do the same eating jalepenos. Never tried the hot sauces myself, after my neurologist was satisfied in seeing my scans that this is likely brain stem related (which would explain why Clonazepam works for me).

EDIT: IMPORTANT: I have geographic tongue/fissured tongue, and suffer from severe mouth ulcers (canker sores). I've had all 3 since childhood.