(See also Overview of Pain Overview of Pain Pain is the most common reason patients seek medical care. Pain has sensory and emotional components and is often classified as acute or chronic. Acute pain is frequently associated with anxiety... read more .)
CRPS type I was previously known as reflex sympathetic dystrophy (see also Complex Regional Pain Syndrome: Treatment Guidelines), and type II was known as causalgia. Both types occur most often in young adults and are 2 or 3 times more common among women.
Etiology of Complex Regional Pain Syndrome
CRPS type I typically follows an injury (usually of a hand or foot), most commonly after crush injuries, especially in a lower limb. It may follow amputation, acute myocardial infarction, stroke, or cancer (eg, lung, breast, ovary, central nervous system); no precipitant is apparent in about 10% of patients. It commonly occurs after immobilization of the limb to treat the initial injury.
CRPS type II is similar to type I but involves overt damage to a peripheral nerve.
Pathophysiology of CRPS
Pathophysiology is unclear, but peripheral nociceptor and central sensitization and release of neuropeptides (substance P, calcitonin gene-related peptide) help maintain pain and inflammation. The sympathetic nervous system is more involved in CRPS than in other neuropathic pain syndromes. Central sympathetic activity is increased, and peripheral nociceptors are sensitized to norepinephrine (a sympathetic neurotransmitter); these changes may lead to sweating abnormalities and poor blood flow due to vasoconstriction. Nonetheless, only some patients respond to sympathetic manipulation (ie, central or peripheral sympathetic blockade).
Symptoms and Signs of CRPS
Symptoms of complex regional pain syndrome vary greatly and do not follow a pattern; they may include sensory, focal autonomic (vasomotor or sudomotor), and motor abnormalities. Symptoms are unilateral; bilateral symptoms at onset suggest a different diagnosis.
Pain—usually burning or aching—is a core diagnostic feature. It does not follow the distribution of a single peripheral nerve; it is regional, even when caused by injury to a specific nerve, as occurs in CRPS type II. It may worsen with changes in the environment or emotional stress. Allodynia and/or hyperalgesia are usually present, indicating central sensitization. Pain often causes patients to limit use of an extremity.
Cutaneous vasomotor changes (eg, red, mottled, or ashen color; increased or decreased temperature) and sudomotor abnormalities (dry or hyperhidrotic skin) may be present. Edema may be considerable and locally confined.
Other symptoms include trophic abnormalities (eg, shiny, atrophic skin; cracking or excess growth of nails; bone atrophy; hair loss) and motor abnormalities (weakness, tremors, spasm, dystonia with fingers fixed in flexion or equinovarus position of foot). Range of motion is often limited, sometimes leading to joint contractures. Symptoms may interfere with fitting a prosthesis after amputation.
Psychologic distress (eg, depression, anxiety, anger) is common, fostered by the poorly understood cause, lack of effective therapy, and prolonged course.
Diagnosis of CRPS
Complex regional pain syndrome is diagnosed when the following are present:
Patients have continuing pain beyond that explained by dysfunction of a single nerve and that is disproportionate to any original tissue damage.
Certain clinical criteria (Budapest criteria  Diagnosis reference Complex regional pain syndrome (CRPS) is chronic neuropathic pain that follows soft-tissue or bone injury (type I) or nerve injury (type II) and lasts longer and is more severe than expected... read more ) are met.
The Budapest criteria have four categories. For CRPS to be diagnosed, the patient must report at least one symptom in three of the four categories, and the clinician must detect at least one sign in two of the same four categories (symptoms and signs overlap):
Sensory: Hyperesthesia (as a sign, to pinprick) or allodynia (as a sign, to light touch, deep somatic pressure, and/or joint movement)
Vasomotor: Temperature asymmetry (> 1° C as a sign) or asymmetric skin color changes
Sudomotor or edema: Sweating changes, sweating asymmetry, or edema
Motor or trophic: Trophic changes in skin, hair, or nails, decreased range of motion, or motor dysfunction (weakness, tremor, dystonia)
Also, there must be no evidence of another disorder that could explain the symptoms. If another disorder is present, CRPS should be considered possible or probable.
Bone changes (eg, demineralization on x-ray, increased uptake on a triple-phase radionuclide bone scan) may be detected and are usually evaluated only if the diagnosis is equivocal. However, on imaging tests, bone may also look abnormal after trauma in patients without CRPS, making abnormalities detected by x-rays and bone scans nonspecific.
In one test of sympathetic involvement, a patient is given IV infusions of saline (placebo) or phentolamine 1 mg/kg over 10 minutes while pain scores are recorded; a decrease in pain after phentolamine but not placebo indicates sympathetically maintained pain.
Sympathetic nerve block (cervical stellate ganglion or lumbar) has been used for diagnosis (and is used for treatment). However, false-positive and false-negative results are common because not all CRPS pain is sympathetically maintained and nerve block may also affect nonsympathetic fibers.
Prognosis for CRPS
Prognosis varies and is difficult to predict. CRPS may remit or remain stable for years; in a few patients, it progresses, spreading to other areas of the body.
Treatment of CRPS
Multimodal therapy (eg, drugs, physical therapy, sympathetic blockade, psychologic treatments, neuromodulation, mirror therapy)
The primary goal of all treatments for complex regional pain syndrome is to increase the mobility and use of the affected limb.
Treatment of CRPS is complex and often does not result in complete relief of symptoms, particularly if begun late. It includes drugs, physical therapy, sympathetic blockade, psychologic treatments, and neuromodulation. Few controlled trials have been done.
Many of the drugs used for neuropathic pain Drugs for Neuropathic Pain , including tricyclic antidepressants, antiseizure drugs, and corticosteroids, may be tried; none is known to be superior. Long-term treatment with opioid analgesics Opioid Analgesics Nonopioid and opioid analgesics are the main drugs used to treat pain. Antidepressants, antiseizure drugs, and other central nervous system (CNS)–active drugs may also be used for chronic or... read more may be useful for selected patients. Neuraxial infusion with opioids, anesthetics, ziconotide, and/or clonidine may help, and intrathecal baclofen may reduce dystonia.
The goals of physical therapy Physical Therapy (PT) Physical therapy aims to improve joint and muscle function (eg, range of motion, strength) and thus improve the patient’s ability to stand, balance, walk, and climb stairs. For example, physical... read more include desensitization, strengthening, increased range of motion, and vocational rehabilitation. In some patients with sympathetically maintained pain, regional sympathetic blockade relieves pain, making physical therapy possible. Oral analgesics (nonsteroidal anti-inflammatory drugs [NSAIDs], opioids, various adjuvant analgesics) may also relieve pain sufficiently to allow rehabilitation.
Desensitization of an allodynic limb involves first applying stimuli that are relatively nonirritating (eg, silk) and, then over time, increasing to more irritating stimuli (eg, denim). Desensitization can also involve thermal contrast baths, in which the affected limb is placed in a cool water bath, then placed in a warm water bath.
Mirror therapy has been reported to benefit patients with CRPS type 1 due to phantom limb pain Complications or stroke Overview of Stroke Strokes are a heterogeneous group of disorders involving sudden, focal interruption of cerebral blood flow that causes neurologic deficit. Strokes can be Ischemic (80%), typically resulting... read more . Patients straddle a large mirror between their legs. The mirror reflects the image of the unaffected limb and hides the affected (painful or missing) limb, giving patients the impression that they have two normal limbs. Patients are instructed to move the normal limb while viewing its reflected image in the mirror. This exercise tricks the brain into thinking that the affected or absent limb is moving without pain. Most patients who do this exercise for 30 minutes a day for 4 weeks report a substantial reduction in pain.
For neuromodulation, implanted spinal cord stimulators are commonly used; in severe cases with significant functional impairment, they should be considered early. Dorsal root ganglion stimulation may target localized symptoms.
Transcutaneous electrical nerve stimulation Electrical stimulation Treatment of pain and inflammation aims to facilitate movement and improve coordination of muscles and joints. Nondrug treatments include therapeutic exercise, heat, cold, electrical stimulation... read more (TENS), applied at multiple locations with different stimulation parameters, may be effective but requires a long trial.
Acupuncture Acupuncture Acupuncture, a therapy within traditional Chinese medicine, is one of the most widely accepted components of integrative therapies in the western world. Specific points on the body are stimulated... read more may help relieve the pain.
In patients with complex regional pain syndrome, psychotherapy may be used to treat depression and anxiety; it may also help patients successfully improve function and their control over their life despite the chronic pain disorder.
Complex regional pain syndrome may follow injury (to soft tissue, bone, or nerve), amputation, acute myocardial infarction, stroke, or cancer or have no apparent precipitant.
Diagnose CRPS if patients have neuropathic pain, allodynia or hyperalgesia, and focal autonomic dysregulation when no other cause is identified.
Prognosis is unpredictable, and treatment is often unsatisfactory.
Treat as early as possible using multiple modalities (eg, drugs used for neuropathic pain, physical therapy, sympathetic blockade, psychologic treatments, neuromodulation, mirror therapy).
Complex Regional Pain Syndrome: Treatment Guidelines: This web site provides links to two guidelines: Harden RN, Oaklander AN, Burton AW, et al, Complex Regional Pain Syndrome: Practical Diagnostic and Treatment Guidelines, 4th edition (2013) and The Royal College of Physicians, Complex Regional Pain Syndrome in Adults, 2nd edition (2018). These guidelines aim to help health care practitioners effectively treat patients with complex regional pain syndrome and improve their ability to function.