--ever been considered?

Has he had nerve conduction studies and/or electromyelography of his peripheral nerves, or any other tests for antibodies that are associated with motor neuropathies?

Sometimes, the assumption of one condition blinds medical professionals to the possibility of others--and many of us are "co-morbid".

Come on over to the peripheral neuropathy forum:

http://neurotalk.psychcentral.com/forumdisplay.php?f=20

and detail as much of the medical hisotry and tests as you are able; many very insightful people there.