First - your vet is probably correct - it is probably a neurological problem, and more often than not, these are almost impossible to figure out. So -- if your dog is comfortable....don't even go there.
Second - if you run a search, I have posted a couple times about a "shaking dog syndrome." (Just search "shaking" and see what comes up.) You might see if this syndrome describes what your dog is doing.
I have noticed several times in the last month or two - people posting about their dogs "shaking." So, this must not be an uncommon problem with Yorkies. I think you might find it interesting to read some of the other posts.
Good luck! Carol Jean |