I believe that when the dorsal roots (ganglions) along the spine are involved, that is when the symptoms are more global and not just confined to the hands and feet.

There is a dorsal root thread in the subforum:
http://neurotalk.psychcentral.com/thread147771.html

The dorsal roots may be damaged by viruses (shingles is one example) or toxins (chemo or drugs), or autoimmune attack, and this gives the sensory symptoms. On that thread is a paper explaining that when the dorsal roots are involved, EVENTUALLY the nerves in the periphery deteriorate, but that takes time. So the biopsy if taken too early, won't show that much. Two years later, however, there may be some loss.

People vary in how they repair this damage to the dorsal roots.
Evidently some people lack genetic capability to make the nerve growth factors to do this. Hence their symptoms remain, but for others there can be improvement over time. The Herpes Zoster virus is well known for causing long term pain. Some doctors now think other viruses can also cause similar syndromes.