my daughter's problems with pandas were almost all movement based too, several bouts with severe chorea, although cunningham test showed pandas.
she had a brain MRI during the most severe bout when she was hospitalized, under general anasthesia (she was moving/shaking/twitching too severely to go into the machine without sedation), and it was negative.
it seemed like each episode got worse. she had a total of about 4 episodes over the course of about a year, although the first one was probably the most involved (head/neck/eyes, legs/severe dysphagia) . it was just awful and almost no one had ever seen anything like it.
at first, she responded well to abx and steroid bursts, with some valium to keep her still enough to sleep. but, after a while, even that wouldn't work. we had pharesis done in march, and that was the only thing that totally remediated the tics/chorea.
also, she had quite an extensive history of strep and would always test positive. younger daughter would too, but would generally be symptom free. unusual variants of strep.....headaches, stomach aches, rash on rear end, and sometimes throat cultures, generally with no fever. it got to the point where the doctor would just do a rapid strep/culture on both kids before even considering anything else.