Alternative to biopsy?

[Shivakumar S. Nair]

Is there an alternative to a nerve biopsy to distinguish between mononeuritis 
multiplex and demyelinating neuropathy? Both of these have been suggested as 
the possibilities for the neurological illness that my mother is suffering 
from, but nerve conduction studies/MRIs/EMGs have not yielded a conclusive 
answer about the true nature of illness. Her weak condition makes a biopsy a 
last resort.

If anybody has information on any other techniques / diagnostics that can be 
used, could you pl. mail it to me? Or is a biopsy absolutely vital in this 
case?

Thanks,
Shiv