Actually..I remember seeing pictures of Tapeworm cysts in the thigh muscles in xrays...I need to find it again...
but :) that was how House figured out what the woman had going on in her head too...he had them do xrays, looking for cysts in the thigh.
Here's something more for you to read while I'm looking for the xrays again:
A post of Newport's for why the immune system doesn't know to hit the cysts/parasites: