How would you approach the workup of unilateral chorea with a normal MRI?  

I would first rule out Sydenham chorea by checking ASO titers, DNase B titers, ESR, and CRP, and performing an echocardiogram and EKG. I would also recommend an MR angiogram if not already done for Moya-Moya. Following that, I would check copper levels, ceruloplasmin, serum amino acids, serum lactat...

Clinical context is required and the clinical course is highly relevant in determining the underlying pathology. Vascular etiologies and DKA are very high on the differential. I would review the MRI in great detail to ensure a basal ganglia or STN lesion was not missed. If I found nothing, I'd send ...