Complex regional pain syndrome (CRPS) is a form of chronic pain that usually affects an arm or a leg. CRPS typically develops after an injury, a surgery, a stroke or a heart attack. The pain is out of proportion to the severity of the initial injury.

Complex regional pain syndrome is uncommon, and its cause isn't clearly understood. Treatment is most effective when started early. In such cases, improvement and even remission are possible.

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Signs and symptoms of complex regional pain syndrome include:

• Continuous burning or throbbing pain, usually in your arm, leg, hand or foot

• Sensitivity to touch or cold

• Swelling of the painful area

• Changes in skin temperature — alternating between sweaty and cold

• Changes in skin color, ranging from white and mottled to red or blue

• Changes in skin texture, which may become tender, thin or shiny in the affected area

• Changes in hair and nail growth

• Joint stiffness, swelling and damage

• Muscle spasms, tremors, weakness and loss (atrophy)

• Decreased ability to move the affected body part