I would definitely get x-rays of his hip and spine to make sure you really are dealing with arthritis and exactly where the problem lies.
I like Metacam, but if it is causing diarrhea then there are other NSAIDS that could be tried. Rimadyl is good, too. Tramadol is a pain reliever, but not anti-inflammatory and can be given along with the Rimadyl (or by itself) and is less likely to cause diarrhea.
Another thing to consider is acupuncture. I practice next door to a veterinary acupuncturist and have actually taken my older dog there for one treatment so far. They have a lot of old dogs that go there and they all seem to be doing well. So definitely something to consider.
My concern is the vet just wants to put him a drug for the rest of his life, I was the one who suggested the x-rays. She thinks it is a disc issue which won't show on x-rays.
To some degree your vet is correct--a protrusion of a disk on the spinal canal wouldn't show up. With that kind of problem, however, the dog is usually in a lot of pain, not just shaking legs. Is there any neurologic problems? If you flip one for his back paws over (so the toes are pointing back and the top of the paw is on the ground), does he flip the paw over quickly or just leave it there?
So for disk disease and spinal compression, a CT or MRI is the way to go and you would likely need to go to a specialty hospital or vet school for that.
My original concern was a mild acidosis because he had a heat related issue where he woke from sleep shaking all over, panting and pacing, I cooled him off and put him in the car with AC and took to an emergency vet. Got there and shaking stopped, so they said monitor him. That incident is what took me to my vet, to see if that incident might be rtelated to shaking after running and if he had a mild E.R. issue.
But x-rays would certainly tell you if there is arthritis in the hip and/or knee joints, if there was any instability in the lower back, if there was a calcified disk in the spine, etc. That is certainly the place to start. For good hip x-rays, your dog will need some sedation so they can get the appropriate views.
Did your vet do any bloodwork when you took him in the first time?
No neurologic problems, did the flip paw test awhile back. He doesn't even seem to be in pain.
So any bloodwork done?
Is he showing any weakness with exercise or any collapse or limping? Or just the shaking of the rear legs?
Bloodwork was done about 10 days after the heat issue, all normal ranges. Yes, as soon as he gets the shaking legs he lies down. He also doesn't like to stand still on walks, sometimes tries to lie down then. No limping. Newset issue is waking from sleep with a wail of pain, runs holding his rear left leg in the air, I massaged it and he seemed okay, but then the same thing happened about 5 minutes later. His rear legs are very stilted (straight up and down).
I would definitely start with x-rays of hips, knees, and back. And then I would seriously consider trying acupuncture for 3-4 times and see if that helps. There is also a disease called myasthenia gravis, where there aren't enough neurotransmitters in the nerve junctions. The dog basically runs out of energy and has to lie down. After a rest, then the dog can move again, at least for a little while. It isn't painful, however, so doesn't fit with his newest signs.
I do have the name of a vet who does acupuncture and x-rays will be done in September and yes they mentioned sedation to get good shots. The vet is calling me tonight, with a second urinalysis test result, I did another urine sample RIGHT after he ran, since previous urine and bloodwork were 14 days after he last ran and 10 days after the heat incident. I will see what she says about Medicam and the diarrhea.....but if I'm not seeing a change in behaviour (he's been on the Medicam 2 weeks) and I don't even know if he is in pain, should I be looking for another anti-inflammatory? (the two incidents with what seems like leg cramps happened while one week into the Medicam). Okay, thanks for your input. I guess we're on the right track to narrowing things down.
I agree, if he doesn't seem painful (although the holding up the rear leg sounds like pain to me) and he has some diarrhea, I think I would stop the Metacam and see if there is any difference--in how long he goes before he starts shaking, perhaps, or how quickly he gets up from lying down.