Chronic pain as a disease, as opposed to the symptoms of a disease, is discussed in this Elliot Krane speech. The pediatrician, who dedicates his career to managing the pain of children, explains how 10 percent of patients who experience persisting pain after a recovery, are suffering from it in the form of a disease.
He explains how the body's nervous system misinterprets different sensations, causing the body to rewrite parts of its nervous systems that transform the ways it reacts to different stimuli.
As of right now, patients are treated for chronic pain in a rather crude fashion with pain killers and different types of therapy. He sees a future in which drugs will be developed that will go one step further than simply masking the pain -- they will terminate the disease at the root of the problem.