In my studies, I learned that pain and itching are two sides of the same coin. Our bodies, dealing with pain that is chronic sometimes can't send the appropriate signal to our nerves. This ends up causing itching, even though what we're actually feeling is pain. Our bodies are so messed up from the constant pain signals that once in awhile or sometimes a lot, pain comes across as itching. The other possibility is that a lot of the meds we take to relieve the pain can cause our bodies to itch. When it's narcotics, it's usually not a true allergy where it's leads to anaphylaxis - it's a known side effect of these kinds of drugs.