vets, UGA vet schoo? My 11 year old beagle, George, is sick.

This is a list of symptoms, what tests have been preformed, and what has been ruled out by several different vets.
-Wobbly, muscle weakness, loss of appetite (all developed progressively in last 6 months)
-he currently is taking 10mg prednisone which helps a little with his appetite and wobblyness
-no noticeable pain
-MRI and full body x-ray showed no tumors
-spinal tap showed no autoimmune disease
-Complete blood count came back normal
-tested negative for myasthenias gravis
-tested negative for Addison's disease

-only eats apple sauce, yogurt, babyfood and dehydrated chicken strips (and baby vitamins (iron free) i squirt down his throat)

Now I know that 11 years old is pretty old.. but this is not just old age kicking in. There is something wrong with him, and nobody can figure it out!!

Please help or make suggestions if this sounds like something you have seen or experienced!