Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) is persisting limb pain out of proportion to the inciting event, with sensory, vasomotor, sudomotor or oedema, and motor or trophic changes.

It usually follows a fracture (classically of the distal radius), surgery, a soft tissue injury or immobilisation, with no relationship to the severity of trauma; about 1 in 10 cases have no obvious trigger. Type I has no major nerve lesion and is much more common; type II follows a major nerve injury. The clinical picture is the same.

Women are affected more than 3 times as often as men, most often after the menopause.

Prompt diagnosis and early active rehabilitation are considered best practice (Royal College of Physicians, RCP, 2018).

The cause is unknown; peripheral and central mechanisms interact:

• •Peripheral inflammation: an exaggerated neurogenic inflammatory response (substance P, CGRP, cytokines) gives warmth, redness and oedema
• •Central sensitisation: disproportionate pain, allodynia and hyperalgesia
• •Cortical reorganisation: the limb may feel foreign or distorted
• •Autonomic dysfunction: presentations are described as warm (red, swollen) or cold (blue or mottled, sweaty) and may change over time; the older idea of fixed stages is obsolete
• •Motor and trophic change: weakness, tremor, dystonia, stiffness, hair, nail and skin changes

CRPS is not associated with pre-existing psychological problems, somatisation or malingering. Anxiety and fear of movement can amplify and maintain it.