Your vet may have meant a condition which can not be treated as there are neurlogical issues which are un-treated.
Have you had a bile acid test performed? Those symptoms are classic for liver shunt including the fact he's getting worse as time progresses. The longer LS isn't treated the more damage that occurs to the liver. Those medicines would have no effect in treating him for this but could make the situation worse.
Link with more information....
Portosystemic Shunts FAQ