You should have a MRI done of your son he may have a Chiari Malformation. Duke University has confirmed there is a co-occurence of these conditions. In persons with Autism sometimes they don't feel pain or relate it the same way as typical persons may. If you would like more info please email me. I have a community on line that talks about this. Don't ignore this. Most doctors think of a Chiari as insignificant. It is not. If your son had an MRI a long time ago, it may not have showed up on that one, or been ignored.