CRPS (Complex Regional Pain Syndrome) is a chronic pain condition that typically starts after an injury or surgery to a limb, but the exact cause is not fully understood. Most current explanations point to a multifactorial origin involving the nervous system, immune/inflammatory processes, and changes in the brain and spinal cord that amplify and mislocalize pain signals. Common themes include peripheral nerve injury or dysfunction, central nervous system sensitization, autonomic (sympathetic) nervous system involvement, and inflammatory or autoimmune-like responses. Genetics may play a role in susceptibility, though no single cause has been identified. Key factors often discussed as contributors or triggers

• Nerve injury or trauma: CRPS frequently follows fractures, sprains, surgery, or other injuries, suggesting a link between nerve damage and symptom development.
• Autonomic dysfunction: Abnormal regulation of blood flow, sweating, and temperature in the affected limb is a hallmark of the condition, indicating sympathetic nervous system involvement.
• Neuroinflammation and immune responses: Inflammatory mediators and immune system activity may sustain or worsen pain and swelling.
• Central sensitization: The central nervous system may become hyper-responsive to stimuli, leading to amplified pain signals even after the initial injury has healed.
• Multisystem interactions: Vascular changes, bone turnover alterations, and changes in cortical representation of the affected limb can occur over time.

Clinical implications

• Onset is often in a limb, with symptoms such as ongoing burning or sharp pain, sensitivity to touch, swelling, color or temperature changes, and reduced range of motion.
• The condition is sometimes labeled CRPS type I (no confirmed nerve injury) or CRPS type II (with identified nerve injury).
• Diagnosis is clinical, supported by history and physical examination; there is no single definitive test.
• Early recognition and multidisciplinary treatment improve outcomes and may include physical/occupational therapy, pain management strategies, medications targeting nerve signals or inflammation, psychological support, and, in some cases, interventional procedures.

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