Children with ADHD are often very tolerant of pain, and don't focus on injuries.
JD - I've heard of what you're talking about, but it seems like that's a different syndrome. Those kids can't learn things like don't burn yourself, don't fall off high places, etc., because they literally don't feel anything as painful. I think what the OP is talking about is a high level of pain tolerance.
My son also picks and chews his finger tips to point of bleeding. -- your words
The "picking" of skin is a behaviour common to OCD. Sensory issues are usually co-morbid with anxiety issues so your statement about "sensory" was more or less expected.
I read on the internet that the gene SCN9A is the one which, if it has a default, the person cannot feel pain. I also read that Resperidone (an anti-psychotic medication) is used for ADHD and pediatric schizophrenia. Co-incidentally, children who suffer from "no pain" often suffer from schizophrenia. Not to scare you - but I think I would address these questions to your family doctor/psychologist/psychiatrist. ODD is a very serious diagnosis and often is used by the mental health field to "cover" areas where the suspected diagnosis cannot be given until the person is an adult. I also noticed that there is a Schizophrenia Forum on this site - maybe someone on that board will be able to offer more concrete information or be able to refute the information I found. I wish you the best ...