This has been happening to me again, the endo says my levels are fine but this just started 2 weeks ago and before that hadn’t hapened since right after my RAI (before diagnosis it had been going on for years). You summed up exactly what happens to me. I get a tickle that i lightly scratch, even if i just brush over it, and then it spreads like a brush fire. Usually only on my legs but it has occurred elsewhere. I can’t scratch fast or hard enough and it travels. My legs are red and have welts by the time i am done. Usually i grab ice cubes and rub them on my legs until they stop burning, it usually makes the itching stop. I don’t know what this is or why but it is maddening that is for sure.