dog has trembling right leg.

Question
Hi Labman,
My family adopted an 8 week old black lab from the shelter. He is now 17 weeks old. Beginning at 8 weeks we had all vaccinations done in a timely manner. Besides a FEW (4 or 5) bouts of diarrhea, he has been perfectly healthy.
Suddenly 4 days ago he began having tremors in his right shoulder. He tremors consistently but is able to run and play with tons of energy, but when he tries to rest he cries. After taking him to the vet they felt he has post-distemper. No tests were run, it was concluded from the tremors. He hasn't been sick at all. None of the symptoms I found on-line sound familiar at all. Can you think of any other source of tremors in Lab puppies that this may be?  

Answer
Even the best shot programs leave windows where a puppy can pick up things.  I would think if he had distemper, you would have seen problems.  I have no other ideas.  I would keep an eye on it.  Remind the vet of it as you should have him back for rabies and neutering.