Complex regional pain syndrome (or Sudek's atrophy) is a complex disorder that occurs in the absence of nerve injury, characterised by pain, abnormal blood flow, trophic changes to the skin, sensory disturbance and autonomic features.
It can be caused by many orthopaedic operations, fractures, herpes zoster or the cause may be unknown (idiopathic).
It presents weeks to months after an initial insult and in the neighbouring area. Patients may complain of allodynia, hyperalgesia or even neuromuscular features such as weakness. It is normally self-limiting but can be treated with amitriptyline, gabapentin or sympathetic nerve blocks.