I completely agree with Jaybay. The "best" vet would be the one who is able to diagnose what is wrong with your dog. Everyone is capable of missing a diagnosis, even the most qualified doctors mess up sometimes, after all, they're only human. I would take her to another vet to see if maybe they can spot something that the other doctor missed.
Ghilly
"Best" only applies if he's successful (in my humble opinion). Even the best and most expensive vets can get stuck once in awhile. I learned that hard lesson myself with human doctors. The "best" one is the doctor who can diagnose and treat the problem.
You might get some ideas from one of our vets here at Med Help on the Ask a Vet forum. in addition, they might be able to refer you to another facility in your area. Post all the test results you have including labs and imaging studies to help them give you the best advice possible. I'm hoping and praying your dog gets a diagnosis very soon.
Got the Blood test twice and urine test once but report is normal. i would look for other Dr. but the existing DR is the dean of Vet science. i feel he is the best in state.
Checked on net also but still no information is available on such instances.
How about getting a 2nd opinion from a different vet? Since your own vet admits defeat, he should have no trouble with that decision. Actually, I admire any doctor who admits when he's baffled; but he should send you on to someone else. You might ask him to refer you to a specialist in your area. Something is obviously very wrong, and the fast weight loss is extremely worrisome. Did your vet do any x-rays or blood & urine work only?