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Complex regional pain syndrome (CRPS)
Complex regional pain syndrome (CRPS) is a condition marked by severe, prolonged chronic pain (lasting more than six months) that may be constant. Symptoms vary in intensity and duration. Some people describe it as a burning sensation, a "pins and needles" sensation, or as if an arm or leg is being squeezed. The pain may spread to the entire arm or leg, even though the injury may have been only to a finger or toe. Common symptoms include dramatic changes in the color and temperature of the skin over the affected limb or body part, accompanied by intense burning pain, increased sensitivity in the affected area, skin sensitivity, abnormal sweating, and abnormal movement in the affected limb. In most instances the condition is triggered by a clear history of trauma or injury. CRPS also affects the immune system -- the disorder is more common in individuals with other inflammatory and autoimmune conditions such as asthma. Limited data also suggests that CRPS may also be influenced by genetics.
Central and peripheral sensitisation
Following tissue damage and/or neuronal injury, alterations in the central and peripheral nervous systems lead to increased inflammation, and an enhanced responsiveness to pain. These adaptations act as protective mechanisms to promote avoidance of activities that cause further injury. Within the central nervous system (CNS), persistent and intense noxious stimulation of peripheral nociceptive neurons results in central sensitisation. Accordingly, there is alteration in nociceptive processing in the CNS and increased excitability of secondary central nociceptive neurons in the spinal cord. This is mediated by the release of neuropeptides such as substance P, bradykinin and glutamate by peripheral nerves, which sensitise and increase the activity of local peripheral and secondary central nociceptive neurons resulting in increased pain from noxious stimuli (hyperalgesia) and pain in response to non-noxious stimuli (allodynia) [26, 32, 33]. Research has shown that CRPS patients have a significantly greater windup to repeated stimulation of the affected limb compared to the contralateral limb or other limbs [34, 35].
There is no cure for CRPS and no drug has been approved specifically for the disorder. Treatments are aimed at relieving painful symptoms. Doctors may prescribe topical analgesics, antidepressants, corticosteroids, and opioids to relieve pain, but no single drug or combination of drugs has produced consistent long-lasting improvement in symptoms. Other treatments may include physical therapy, nerve blocks, spinal cord stimulation and other types of neurostimulation, and surgery.
The prognosis for CRPS varies highly from person to person. Early treatment, particularly rehabilitation, may help with limiting the disorder. Younger people, children, and teenagers tend to have better outcomes. Some older adults have good outcomes while others continue to experience severe pain despite treatment.