Complex regional pain syndrome and functional neurological disorders – time for reconciliation

Correspondence to Professor Jon Stone, Department of Clinical Neurosciences, Western General Hospital, Edinburgh EH4 2XU, UK; [email protected]

Introduction

Complex regional pain syndrome (CRPS) is a disabling chronic pain condition that may follow physical injury to a limb, either through surgery or trauma. Previously, there were no clear diagnostic criteria, and a mixture of terminologies were used, such as ‘Reflex Sympathetic Dystrophy’ and ‘Causalgia’. In response to this, the International Association for the Study of Pain introduced a new terminology in an attempt to standardise diagnosis and management: CRPS type I, where there was no defined nerve lesion and type II, where there was a definite nerve lesion. These definitions have since been superseded by the Budapest clinical and research criteria (box 1).^{1 2} CRPS occurs in around 20 out of 100 000 patients, with more women than men being affected, most commonly in the 37–53 year age range. It is characterised by local inflammatory and autonomic dysregulation combined with trophic and motor dysfunction of the affected body part.² Although its defining features (sensory, autonomic, motor and trophic) have been extensively studied, their pathophysiological nature and the role of the incipient event remain a matter of debate and research.²

Box 1

Budapest clinical diagnostic criteria for CRPS,² with features also seen in functional neurological disorder italicised

• Continuing pain, which is disproportionate to any inciting event.

• Must report at least one symptom in three of the four following categories:

  • Sensory: reports of hyperaesthesia and/or allodynia.

  • Vasomotor: reports of temperature asymmetry and/or skin colour changes and/or skin colour asymmetry.

  • Sudomotor/oedema: reports of oedema and/or sweating changes and/or sweating asymmetry.

  • Motor/trophic: reports of decreased range of motion and/or motor dysfunction (weakness, tremor, dystonia) and/or trophic changes (hair, nail, skin).

• Must display at least one sign at time of evaluation in two or more of the following categories:

  • Sensory: evidence of hyperalgesia (to pinprick) and/or allodynia (to light touch and/or deep somatic pressure and/or joint movement).

  • Vasomotor: evidence of temperature asymmetry and/or skin colour changes and/or asymmetry.

  • Sudomotor/oedema: evidence of oedema and/or sweating changes and/or sweating asymmetry.

  • Motor/trophic: evidence of decreased range of motion and/or motor dysfunction (weakness, tremor, dystonia) and/or trophic changes (hair, nail, skin).

• There is no other diagnosis that...