trying to post a pic..

perhaps cold damage?

I can't say that I have ever seen bark discoloration quite that pronounced :-) Typically one sees the reverse or the top portion of the branch - the part exposed to sunlight - scorching or discoloring. Having said that, there are a number of diseases that affect Japanese maples that can result in both branch/stem dieback as well as discoloration of the wood. Just unlikely to be so precise with that discoloration:-)

The various maple pathogens can look remarkably alike, so an accurate diagnosis is best left to a plant pathologist. Some can be debilitating and damaging; others can be fatal and there is seldom an easy cure. Pruning out obviously dead wood is aways appropriate - just sterilize pruners after each cut.

I think verticillium wilt is a strong possibility. You can read up on it at the link below & see if that fits your symptom profile.

Al

Here is a link that might be useful: More on wilt