Introduction to complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a chronic pain syndrome in which the severity of pain is disproportionate in time or degree to the inciting event. The inciting event may be trauma (eg distal radius fractures are the most common cause in adults), surgery, or a medical condition (eg stroke). The inciting event is often trivial (eg a wasp sting) and difficult to identify, particularly in children. There are two types of CRPS, separated by the absence (Type I) or presence of nerve injury (Type II).

CRPS affects the limbs—upper limbs more frequently in adults and lower limbs more frequently in children. Pain is worst in the most distal part of the extremity. It is often described as a spontaneous burning sensation distally, which increases when the limb is hanging. The pain is not limited to the distribution of a peripheral nerve or root, and its severity is out of proportion to that expected—consider CRPS if limb pain is disproportional to the injury, then assess for other diagnostic criteria, see Diagnostic criteria for complex regional pain syndrome.

It is not clear why only some individuals develop CRPS following injury or surgery. The pathophysiological basis for CRPS is uncertain, with the condition exhibiting inflammatory, neuropathic and nociplastic features. It is difficult to direct management; see Managing complex regional pain syndrome