I DID ask my Neurologist and pain mgmt specialist about this. He too was stumped. Said it sounds like it has to be coming from the arachnoid cyst on my thoracic spinal cord area, but he's never heard of this either. I told him the itching migrated from 100% of the time on my left nipple, to now about 60% of the time on my nipple, and the other 40% of the time on my upper arm, underside......

He said he'd ask around, see if he can find any info on it. I'm still itching, it's maddening! Scratch, scratch, scritch, scratch!