http://www.hnpp.org/varieties.htm

Scroll down to "Progression of HNPP". As you can see it can be slow for some and rapid for others. Not saying he has this but it might be worth having DNA testing for it. Actually, the whole site on HNPP is very interesting.

Not saying at all that he has this but it would be worth checking out. And to have a neurologist who knows about this.