Complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a poorly understood condition where a person experiences persistent severe and debilitating pain. Although most cases of CRPS are triggered by an injury, the resulting pain is much more severe and long-lasting than normal. The pain usually only affects 1 limb, but it can sometimes spread to other parts of the body. The skin of the affected body part can become so sensitive that a slight touch, bump or even a change in temperature can cause intense pain. Affected areas can also become swollen, stiff or undergo fluctuating changes in colour or temperature. CRPS often gradually improves over time. But some people with CRPS experience pain for many years.

Source: NHS