Complex Regional Pain Syndrome

A chronic pain condition typically affecting a limb, characterised by disproportionate pain accompanied by sensory, autonomic, motor and trophic changes, usually following an initiating injury or surgery, though the resulting pain and dysfunction are markedly out of proportion to the inciting event.

Classification

Type one occurs without evidence of a definable nerve lesion, historically termed reflex sympathetic dystrophy, and is the commoner presentation, typically following fracture, surgery or immobilisation.

Type two occurs in association with a clearly identifiable peripheral nerve injury, historically termed causalgia.

Pathophysiology

An incompletely understood combination of exaggerated neurogenic inflammation, central and peripheral sensitisation, autonomic nervous system dysregulation, and in some cases evidence of an autoimmune component, converges to produce the characteristic clinical picture. The disproportion between the severity of the presentation and the often trivial nature of the inciting injury is a defining and often clinically challenging feature.

Pain that is continuous, disproportionate to the inciting event, and typically burning, throbbing or aching in character, is the central feature, frequently accompanied by allodynia (pain from a normally non painful stimulus) and hyperalgesia.

Sensory changes include altered temperature and touch sensitivity, and asymmetry compared with the contralateral unaffected limb.

Autonomic changes include altered skin colour (mottled, red or cyanotic), temperature asymmetry (the affected limb may be warmer or cooler than the contralateral side, and this can vary over the disease course), and abnormal sweating.

Motor changes include weakness, tremor, dystonia and reduced range of motion, with a tendency toward disuse and guarding that compounds the functional impairment.

Trophic changes, developing with longer disease duration, include altered hair and nail growth, skin texture changes, and in advanced disease, osteopenia of the affected limb.

Symptoms typically follow a specific limb distribution rather than a classical dermatomal or peripheral nerve pattern in type one disease, an important distinguishing feature from other neuropathic pain conditions.

Diagnosis is clinical, based on established criteria (the Budapest criteria) requiring continuing pain disproportionate to any inciting event, together with at least one reported symptom and one demonstrated sign in three of four categories (sensory, vasomotor, sudomotor or oedema, and motor or trophic), with no other diagnosis better explaining the presentation.

There is no single confirmatory diagnostic test, and the diagnosis rests on careful clinical assessment and exclusion of alternative explanations.

Plain radiography may show patchy osteopenia in established disease, and triple phase bone scintigraphy can show characteristic increased periarticular uptake, though neither is required for diagnosis and both have limited sensitivity, particularly early in the disease course.

Thermography and quantitative sensory testing are used in specialist settings to objectively document autonomic and sensory abnormalities where available.

Exclude alternative explanations for the presenting symptoms, including infection, deep vein thrombosis, peripheral nerve entrapment, and an underlying undiagnosed fracture or other structural injury, since complex regional pain syndrome remains a diagnosis of exclusion in the context of a compatible clinical picture.

Early recognition is important given evidence that prompt diagnosis and treatment improve outcomes, so a high index of suspicion is warranted in any patient with pain disproportionate to an inciting injury, particularly with accompanying autonomic or trophic features.

Early, active, function focused physiotherapy and occupational therapy is the cornerstone of management, using graded exposure and desensitisation techniques including graded motor imagery and mirror therapy, with the aim of restoring function and interrupting the cycle of guarding and disuse that perpetuates the condition.

Pain management is multimodal, drawing on neuropathic pain agents (gabapentinoids, tricyclic antidepressants, serotonin noradrenaline reuptake inhibitors) and, for more severe or refractory pain, referral to specialist pain management services.

Corticosteroids may benefit patients with a significant inflammatory component, particularly early in the disease course, though evidence is limited and use is generally individualised.

Bisphosphonates have evidence for benefit, particularly where bone scan or radiographic changes suggest significant bone involvement.

Sympathetic nerve blocks are used by some specialist services for diagnostic and therapeutic purposes, though evidence for sustained benefit is mixed and use has declined in favour of the multimodal functional restoration approach.

Psychological support, including cognitive behavioural therapy, addresses the substantial psychological burden of chronic disabling pain and supports engagement with the functional rehabilitation programme, recognising the bidirectional relationship between pain, mood and function in this condition.

Spinal cord stimulation and other interventional pain procedures are reserved for severe, refractory disease that has not responded to full conservative management, delivered through specialist pain services.

Early referral to a multidisciplinary pain service is appropriate given evidence that early, intensive, coordinated management improves the likelihood of functional recovery and reduces the risk of the condition becoming chronic and treatment resistant.