"Complex regional pain syndrome (CRPS) is chronic neuropathic pain that follows soft tissue or bone injury (type I) or nerve injury (type II) and persists out of proportion in intensity and duration to the original tissue damage." (Complex Regional Pain Syndrome in The Merck Manual, 18th Edition. 2006:1780-81)
Older terms that are still used to describe complex regional pain syndrome are reflex sympathetic dystrophy and causalgia.
CRPS usually follows an injury (typically to an extremity, such as a hand, foot, or ankle) or a painful syndrome (heart attack, cancer, etc.). About 10% of CRPS sufferers do not experience any precipitating event.
The underlying cause of CRPS is not known, but the signs and symptoms of the syndrome appear to be related to a disordered release of neurotransmitters—particularly in the sympathetic nervous system—that are responsible for pain perception.
Gating of Neurotransmitters and Chronic Pain
Whenever tissue injury occurs, specialized receptors within the tissues initiate the flow of messages along neurons that carry pain messages to the brain. This is a vital survival mechanism that prompts an organism to move away from a painful stimulus.
However, nerves don’t follow a continuous conduit from peripheral organs and tissues all the way to the brain. Rather, they are interrupted at various points along their courses by narrow spaces called synapses (sin-APP-sees).
In essence, a synapse acts like a gateway, monitoring the messages that pass through it.
When a message (called an impulse) reaches a synapse, the message must be propagated across the gap by chemical packets that are produced by the sending neuron. These packets then adhere to receptors in the membrane of the receiving neuron, which triggers an impulse in the receiving neuron that is carried onward toward the brain.
If a pain receptor repeatedly sends messages along a neuron, eventually there is an “upgrading” of the neuron’s ability to transmit an impulse…the pathway for the message becomes well-worn and more easily traveled, and the gate swings open more readily.
Sometimes, even when the tissue damage that resulted from the original injury has long healed, the neurons connected to the tissues (as well as pain centers within the brain) “think” the injury is still there. The gates continue to swing open freely to any impulse that travels along the neuron, and the brain continues to interpret the messages as painful stimuli.
Signs and Symptoms of Complex Regional Pain Syndrome
Symptoms in the affected area are variable and do not adhere to a predictable pattern:
- Aching or burning pain; usually does not follow the distribution of a single peripheral nerve; may worsen with environmental stimuli (e.g., cold, warmth) or emotional stress
- A sense that the affected extremity is weak, unable to bear weight, or heavy
- Changes in skin color (red, mottled, or ashen)
- Changes in skin temperature
- Changes in skin hydration (excessively dry or sweaty)
- Edema (swelling)
- Decreased range of motion
- Hair loss, shiny skin, cracked or thickened nails, and contractures may occur in chronically-affected extremities
- Depression often results from lack of effective treatments, poor understanding among medical providers, and chronic course of symptoms
Diagnosis of Complex Regional Pain Syndrome
The diagnosis of CRPS is based on clinical findings and a history of injury (although one in ten individuals has no such history).
If the diagnosis cannot be made on clinical impressions alone, other modalities may provide confirmatory information:
- Thermography may document temperature changes
- *X-ray may show demineralization of bones in an affected extremity
- *Radionuclide bone scanning might reveal abnormalities consistent with CRPS
- Sympathetic nerve blockade can be used for both diagnosis and treatment, although some cases of CRPS are not maintained by the sympathetic nervous system
*Imaging tests can also be abnormal following injury in patients who do not have CRPS (Koman L, et al. Complex regional pain syndrome. Instr Course Lect 2005;54:11-20)
Prevention and Treatment of Complex Regional Pain Syndrome
Early, appropriate mobilization and physical therapy are helpful for preventing CRPS following an injury. Once CRPS is established, rehabilitative physical therapy is essential.
Medications that have shown some utility in treating CRPS include:
- Tricyclic antidepressants (e.g., amitriptyline, nortriptyline) help to restore normal “gating” of nerve impulses
- Anticonvulsants (gabapentin [Neurontin] has shown particular promise for treating chronic pain)
- Corticosteroids
- Muscle relaxants
- Anti-spasmodics
- Nonsteroidal anti-inflammatories (ibuprofen, naproxen, etc.)
- Opioid analgesics (i.e., narcotics) should be avoided if possible, but may prove useful for certain patients
Other modalities:
- Transcutaneous electrical nerve stimulation (TENS) deserves a long trial in all CRPS patients
- Acupuncture
- Neuraxial infusions of narcotics, anesthetics, or sympathetic nerve blockers
- Intrathecal infusion (i.e., directly into the spinal canal) of anti-spasmodic or analgesic medications
Complex regional pain syndrome is a frustrating and disabling condition that often resists treatment. Early mobilization and physical therapy are key ingredients in a therapeutic regimen.
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