Atlantoaxial Instability

[Judy]

I have mild atlantoaxial instability due to Rheumatoid Arthritis. I have facial numbness that comes and goes many times per day. I can make it come and go by changing my position. I have seen a neurologist and neurosurgeon. I have had numerous tests including MRI brain, cervical, x-rays, blood tests, etc. They are reported to be normal, except mild instablity and a c5/6 herniation supposedly not touching anything important.
The instability is estimated at about 4 mm.  

I have been told the nerve for the face is in the brain and therefore the atlantoaxial instability could not be the cause of the facial numbness.

However, I have found the following in reference to the trigeminal nerve:
"The sensory root terminates in the largest of the cranial nerve nuclei which extends from the pons all the way down into the second cervical level of the spinal cord."

Is it true that pain is caused by pressure on the nerve and numbness is caused by pressure on the nerve root?

If so, this seem like a possible cause to me. To me it even seems probable considering many other normal tests.

What do you think; is it possible?, if so, how would one determine that is the cause? what is the treatment?

Thank you so much for your thoughts on the matter.

[Judy - Follow-up question]

Do you have the atlantoaxial instability (C1/C2)- Feels like a LOOSE HEAD?

[CCF Neuro[P] MD, RPS]

Dear Judy:

Sorry to hear about your pain.  I would agree with your physician about the trigeminal nerve and your facial pain and numbness concerning the alantoaxial instability.  Let me explain.  You are correct in thinking that the spinal nucleus (subnucleus of the trigeminal nucleus) of the sensory nucleus of the trigeminal nerve runs from the midbrain to C2 level.  First, the atlantoaxial part of the spinal column lies outside the spinal cord and therefore not involved in the processing that occurs in this nucleus, unless it begins to impinge on the cord or compress the cord.  Yours does not seem to be that unstable as of yet.  Most of the fibers that carry pain and temperature sensation from the face to the trigeminal nucleus lie in the pons and upper medulla and not in the lower C1 and C2 area.  The fibers that enter this nucleus, enter and exit in the pons and medulla area, not in the lower areas.  So anatomically, the description of the instable atlantoaxial is likely not the cause of your pain and numbness.

My guess would be that the pain and numbness might be caused by your rheumatoid arthritis.  Not only will pressure cause nerve dysfunction, but also inflammation of the nerve.  This might be happening in your case.  As the trigeminal nerve exits the skull to innervate the face, the exit sites might be influenced by the arthritis, the nerve itself might be irritated by the inflammatory events induced by the arthritis.  It is difficult to tell, especially over the internet.  

Just for a FYI, pain and numbeness can be caused by many things.  Inflammation, demyelination, conduction block, nerve irritation, pressure, etc.  So, it is not caused just by pressure alone.

Sorry, that I wasn't able to help much.

Sincerely,

CCF Neuro MD