--I am suspicious of the CIDP diagnosis. Not saying that it isn't correct, but there are rather specific clinical criteria for this, including evidence of specific types of demyelination that is traceable upon biopsy or serological evidence from autoimmune attack, as well as a fairly distinctive pattern of reflex abnormalities. I can say, however, that muscle weakness/cramping/spasm is a common symptom of autoimmune demyelinating neuropathies--in fact, in the acute form of CIDP, which is Guillain-Barre syndrome, temporary paralysis of limbs is not uncommon; fortunately your husband seems to have escaped that:

http://neuromuscular.wustl.edu/antibody/gbs.htm#cgbs
http://neuromuscular.wustl.edu/antib...mdem.html#cidp

As you can see from the second link, there are many autoantibodies that can be tested for that might point to another clinical entity, though many of the treatments are similar

Considering the number of cancers he's had, he should be exhaustively tested for paraneoplastic syndromes, which are more common than most doctors think:

http://neuromuscular.wustl.edu/nother/paraneo.htm

Do you have results from all his tests? You can list them here, if you like--we tend to be collectively very good at interpretation here.

I'd also compare them with the Liza Jane spreadhseets for comprehensiveness:

www.lizajane.org