Ahh...poor little guy! These are not symptoms caused by ITP. It sure does sound like some possible reaction to the IVIG, or very possibly, one of the pre-treatments that he's likely being given through the IV, such as Benadryl or Tylenol. I would find out exactly what he's being given and then look up the side effects of each. All drugs have side effects, that is a given. Not every person will have every side effect, of course, but your son might be one of the one's who has this kind of mental reaction.
Do you know if they are giving him Tylenol 3? Feeling like there are bugs crawling on the body is a common symptom of cocaine addicts, so could possibly be a symptom from a codeine-containing medicine, which Tylenol 3 is one (That's why it's prescription only). It may be that he is actually being drugged out of his little mind, and that's why he sits so quietly. There are also some people that are known as ultra-rapid metabolizers, due to a specific gene. They convert codeine into morphine more rapidly and completely than other people. , and so can have more intense or serious side effects than others. And, since we know that Acetaminophen (aka Tylenol), is the LEADING cause of acute liver failure today, I would seriously take a look at this for your little boy; the effects can be cumulative.
And, though they probably haven't told you this (I know they didn't tell me, and my daughter had probably 24 or 25 IVIGs), IVIG is not expected to, nor intended to put him in remission. They know that it will be a way to bring the platelets up quickly, but only temporarily. That's why it's often the go-to treatment for those needing surgery, when they need the count to be higher. The time before counts crash again is variable. For my daughter, the IVIG would bring her counts up only very slightly (btw 10-42) after 2 days. But, they would always fall back to 3-10k by the next week. My daughter had horrible, horrible reactions to the IVIG, and if I'd have been better informed, today, I would never put her through that again.
Like Ann, I would suggest reading more on this site, and exploring the possibility of "watch and wait", or some of the natural treatments. Many children on this board do just that, and while their counts may remain low, at least they needn't endure the awful side effects of the drugs. Btw, my daughter nearly died from two anaphylactic shock reactions--one from Winho, the other from IVIG. And, while they nearly killed her, they did zero for her count.
Instead, she was eventually healed using homeopathic medicine. After 2 small doses, her count went from 11k to 411k in just a few days. There are a few different homeopathic remedies that have this feeling of bugs crawling on them as a symptom. I have used these a few times to help cocaine addicts withdraw more easily, especially when they're having that symptom.
Best wishes,
April