Some nerve damage occurs at the dorsal roots. These are along
the spinal cord. This is where shingles lives, and causes much of its pain.

Damage to the dorsal roots, messes up signals from the periphery and eventually the peripheral nerves atrophy away, because the dorsal root area does not complete the feedback to them properly. (this has been shown in primates so far and is theorized to happen with humans)

this link has details about the dorsal roots:
http://neurotalk.psychcentral.com/thread147771.html

If your dorsal roots are damaged...I don't think applying lidocaine to the wrists would work much or at all.

Do you use solvents, cleaners alot? Apply them without gloves?
Do you exercise and put weight on your palms? Push ups and pull ups can damage the carpal tunnel.

The lidocaine Aspercreme is about $7... so get a tube and apply on the inner wrist areas of both hands and see what happens.
In fact you can try the discussed fingertip wrinkling test with the same product.

http://neurotalk.psychcentral.com/thread225598.html

Compressive neuropathy in the hands most often occurs at the inner wrist where the carpal tunnel is.
It can also occur at the facets of the vertebrae of the spine. This is basically mechanical or traumatic.

The dorsal roots are another location...and this damage is typically viral, infectious, and/or toxin/drug/chem in origin.