Complex Regional Pain Syndrome (CRPS) formerly referred to as Reflex Sympathetic Dystrophy (RSD)
A chronic pain syndrome involving nerve injuries was first described in Civil War casualties. It was not formally defined until the term RSD was introduced to describe a chronic pain syndrome following injury as pain persisted without any nerve lesion.
In 1994 the International Association for Study of Pain (IASP) proposed the change from RSD to CRPS in order to reflect the varied clinical signs and symptoms involved, its regional distribution and that pain was the focus of complaints. Because the sympathetic nervous system is not always involved, the term “sympathetic” was purposefully left out of the name change. The name change also made clear that there is no true understanding of the pathophysiology of CRPS. Two types of CRPS were discussed by the IASP: CRPS-I refers to a chronic pain syndrome that does not have a definable nerve lesion and CRPS-II refers to a chronic pain syndrome that does follow a definable nerve lesion and was previously referred to as causalgia.
The IASP proposed the following diagnostic criteria for a diagnosis of CRPS-I:
- The presence of an initiating noxious event or a cause of immobilization.
- Continuing pain, allodynia or hyperalgesia with pain that is disproportionate to any inciting event
- Evidence at some time of edema, changes in skin blood flow, or abnormal sudomotor activity in the region of the pain.
- This diagnosis is excluded by the existence of any condition that would account for the degree of pain and dysfunction.
The IASP criteria were criticized as being based solely on subjective complaints and failing to require objective clinical documentation. Using the IASP criteria a person with a minor sprain (an initiating event that caused pain with evidence of edema at some point in time) could be diagnosed with CRPS-I.
The Fifth Edition of the AMA’s Guides to the Evaluation of Permanent Impairment set forth objective diagnostic criteria for the definition of CRPS-I. Diagnostic criteria were divided into eleven objective criteria in four categories:
Edema of skin
Abnormal sweat response
Decreased passive range of motion- joint stiffness
Nails brittle or pitted
Hair growth abnormal
Osteoporosis on X-rays
Bone scan is asymmetric
To meet a definition of CRPS-I under the AMA Guides, the presence of eight or more of the eleven criteria must be exhibited concurrently. No single criterion would confirm the diagnosis and the absence of any one criterion would not exclude the diagnosis.
The mechanism of pain transmission in CRPS-I has been extensively studied. An injury occurs, sometimes only a limited trauma that stimulates the peripheral pain receptors referred to as nociceptors. The nociceptors carry the pain sensations to the spinal cord, to stimulate a particular cell column that is called intermediolateral cell column. In the cell column, there are specific neurons that are referred to as Wide Dynamic Range (WDR) neurons. Stimulation of these neurons cause increased sympathetic activity.
This causes a release of norepinephrine in the periphery and has an effect on the blood vessels causing vasoconstriction and pain. It can result in muscle spasms and an increased sensitivity in the periphery to other stimuli whether painful or not.
This leads to recruitment of receptors in the periphery that are not normally functional resulting in allodynia, which is pain from light touch. The application of pain and the response to tissue damage is a reflex response involving the sympathetic nervous system.
The sympathetic nervous system stimulates and leads to vasoconstriction. This leads to more pain and more sympathetic nervous system stimulation causing prostaglandins to build up in nociceptors. It is unknown why this hyperdynamic sympathetic cascade continues even after the tissue injury that initiated this has healed.
CRPS I is divided into three stages: acute, ischemic and atrophic.
The first indication of CRPS-I is prolonged pain usually more severe than the injury. In an individual with CRPS I in Stage 1, initially, there is swelling and redness in the affected area. The acute stage has intense, burning pain or neuralgia, which continues into the dystrophic stage. As the ischemic stage approaches, the pain becomes less. The area is painful, tender, swollen and warm with sweating, and abnormal hair and nail growth.
In Stage 2, which is after weeks or months, the burning pain is exacerbated, there is coolness of the skin; there is hair loss and dystrophic changes over the nails as well as the skin itself. Bone changes, hair and nail changes, discoloration, dystrophy and changes in the skin begin to occur by the second stage. Movements of the joints may become problematic. The area may become pale and develop a decreased temperature, with increased pain and stiffness of ligaments and joints; osteoporosis or osteopenia may become evident.
In Stage 3, the muscles atrophy, contractures form, edema occurs; there is limited range of motion and x-rays show bone loss. The skin will also appear shiny with thin, brittle, sparse hair, nails that are brittle or dystrophic. There can be increased sweating, but it is not normal compared to the other side. The area may become pale and develops a decreased temperature, with increased pain and stiffness of ligaments and joints, and osteoporosis or osteopenia may become even more evident. Color changes including purple can be noted.
In all of the stages, severe chronic pain continues to be a major complaint.
Treatment of CRPS-I must be aggressive and the earlier the diagnosis is made and treatment instituted the better the potential outcome. Treatment consists primarily of occupational and physical therapy, pain control and rehabilitation. Analgesics and neuropathic medication is utilized. Sympathetic blocks have been used.
References available upon request