Can a smpathetic nerve block cause allodynia? i got a ganglion impar block, now i have allodynia in my legs/butt/upper back. started after the block.

Usually opposite: It is usually the opposite. Sympathetic blocks are done usually to treat and/or diagnose disorders of the sympathetic nervous system; reflex sympathetic dystrophy, for example (rsd). It is typically the condition itself (rsd) and not the block that is a more common cause of Allodynia. Don’t hesitate to discuss the specifics of your case with your physician.