Independent of the original cause, there are other factors contributing to chronic pain.
Constant pain changes neural pathways. With persisting pain nerve receptors, brain cells and the “messenger” neurons in the spinal cord get sensitised over time. This is called central sensitisation as is happens mostly in the central nervous system.
Research has identified various mechanisms at spinal cord level (e.g. wind-up) and in the brain (neuronal reorganisation) behind these changes. As results of sensitisation a painful stimulus elicits a stronger and longer lasting response, triggers a painful response to not normally painful sensations (such as touch or temperature) and changes neighbouring nerve cells so that pain can spread to a wider area. This is experienced as intensifying and spreading pain and hypersensitivity. This happens independently of the cause of pain, so even if the painful condition is stable the pain can intensify.
The mind is often struggling to cope with pain and it's consequences. Results can be anxiety, anger, frustration, sadness, low self-esteem, changes in daily routine, behaviour and personality. These are often first spotted by partners and friends. Typically, sufferers have to reduce physical and social activities, which in turn results in isolation and makes life rotate around the pain problem more and more. The changes of emotions and life-situation tend to further worsen the pain experience and so a self-reinforcing spiral is set in motion.
As a result of these factors the persisting pain becomes a disease of it's own; pain doesn't serve a useful purpose any more. So controlling the pain and it’s consequences becomes the focus of pain specialist treatment.