Excerpt from Reflex Sympathetic Dystrophy

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Background

In 1994, the International Association for the Study of Pain (IASP), after development of consensus by a group of pain medicine experts, suggested that the term complex regional pain syndrome (CRPS) should replace reflex sympathetic dystrophy (RSD) and causalgia—CRPS type 1 for RSD, and CRPS type 2 for causalgia. However, the IASP diagnostic criteria were never fully validated, and several pain specialists raised concerns about their clinical and scientific value. The criteria have poor diagnostic specificity and may result in overdiagnosis of CRPS.

RSD is a descriptive term meaning a complex disorder or a group of disorders that may develop as a consequence of trauma affecting the limbs, with or without an obvious nerve lesion. RSD also may develop after visceral diseases or CNS lesions or, rarely, without an obvious antecedent event. It consists of pain and related sensory abnormalities, abnormal blood flow and sweating, abnormalities in the motor system, and changes in structure of both superficial and deep tissues ("trophic" changes). Not all components need be present.

The term "reflex sympathetic dystrophy" is intended to be used in a descriptive sense and does not imply specific underlying mechanisms. Most of the definition of RSD can be applied equally well to causalgia; however, CRPS type 1 (ie, RSD) occurs without a definable nerve lesion, while type 2 (ie, causalgia) refers to cases in which a definable nerve lesion is present.

Evans described RSD as a syndrome with the following manifestations:

• Pain and swelling at a site remote from the inciting injury
• No obvious local tissue damage
• Altered skin color
• Altered sweat production

On the basis of the description by Veldman et al, diagnosis of RSD can be made if the following clinical grounds are met:

• At least 4 of the following 5 symptoms/signs are present: unexplained diffuse pain, altered skin color, altered skin temperature, edema, reduced active range of motion
• Symptoms aggravated by activity of the extremity
• Symptoms present in an area much larger than and also distal to the primary injury

IASP diagnostic criteria for CRPS are the following:

• The presence of an initiating noxious event, or a cause for immobilization
• Continuing pain, allodynia, or hyperalgesia that is disproportionate to any inciting event in severity
• Evidence at some time of edema, changes in skin blood flow, or abnormal sudomotor activity in the region of pain
• Exclusion of conditions that would otherwise account for the degree of pain and dysfunction. The distinction between CRPS with (type 2) and without (type 1) nerve injury is based on findings on electromyography (EMG) and nerve conduction studies (NCS). The clinical validation of these criteria still is being debated.

Associated signs and symptoms of CRPS listed in IASP taxonomy but not used for diagnosis are as follows:

• Atrophy of hair, nails, and other soft tissues
• Alterations of hair growth
• Loss of joint mobility
• Impairment of motor function, including weakness, tremor, and dystonia
• Sympathetically maintained pain - May be present

Staging has no clinical value, but for historical interest the authors would like to mention that the course commonly was divided into the following 3 stages:

• Acute or hyperemic
• Dystrophic or ischemic
• Atrophic

Pathophysiology

No consensus exists regarding the pathogenic mechanisms involved in RSD. Hypotheses include (1) sympathetic nervous system (SNS) dysfunction leading to sympathetically maintained pain (SMP), (2) peripheral dysfunction, (3) central dysfunction, and (4) inflammatory process.

SNS involvement in the mechanism of RSD/CRPS type 1 is supported clinically by the presence of abnormal temperature and color of the skin as well as altered sweat excretion in the affected extremities. Surgical and chemical sympathectomy can relieve pain in some cases. The prevailing hypothesis is that posttraumatic sympathetic-afferent interaction can be established, so that sympathetic efferents can enhance primary afferent nociceptor activity. The coupling of sympathetic and afferent neurons can occur peripherally or at the level of dorsal root ganglia. Experimental studies have demonstrated that within 2 weeks of a nerve lesion that spares a significant number of axons, electrical stimulation of the sympathetic trunk and injections of catecholamines can activate or sensitize C-nociceptors.

The peripheral dysfunction is related to peripheral denervation and/or sympathetic denervation. Initially, vasodilatation is present in the denervated area. Later, the vasculature may develop increased sensitivity to circulating catecholamines due to up-regulation of adrenoreceptors.

The central dysfunction may be related to the effect of high levels of discharge originating in sensory fibers within the affected extremity. These discharges may induce changes in the autonomic CNS and subsequently an alteration in central autonomic control. Clinically, hyperhidrosis is found in many patients with RSD but cannot be explained by a peripheral mechanism, because unlike blood vessels, sweat glands do not develop denervation hypersensitivity.

Early RSD/CRPS type 1 has an inflammatory component. Substance P and other neuropeptides are considered to be the cardinal mediators of neurogenic inflammation. Analyses of joint fluid and synovial biopsies in patients with RSD have shown an increase in protein concentration, synovial hypervascularity, and neutrophil infiltration. Response of RSD/CRPS type 1 to steroids further supports the notion of an inflammatory process.

Frequency

United States

Surveys of veterans suggest that the incidence of causalgia following injury to a peripheral nerve is 1-5%. Little is known about the epidemiology of CRPS type 1 in the United States or internationally. The reported incidence of CRPS type 1/RSD is 1-2% after various fractures, 2-5% after peripheral nerve injury, and 7-35% in prospective studies of Colles fracture. The likelihood of developing CRPS/RSD is higher if the lesion is distal or if the sciatic nerve is affected.

Mortality/Morbidity

• Despite treatment, many patients are left with varying degrees of chronic pain, atrophic changes, and disability. Pain is the most important factor leading to disability.
• Some have suggested that aggressive treatment of pain in an acute setting could reduce the incidence of CRPS type 1/RSD, although further studies are needed to support this observation. Remissions followed by relapse also have been described.
• The frequency of the HLA-DQ1 antigen appears to be higher in patients with CRPS type 1 than in controls. However, no genetic marker is known for CRPS type 1/RSD.

Race

RSD affects all races; no racial predilection is observed.

Sex

A female predominance exists; female-to-male ratio is 2:1.

Age

• Mean age of patients at their initial evaluation in pain centers is approximately 40-42 years.
• The highest incidence of the disease appears to be in adults aged 40-49 years; it appears frequently in almost every age group except children. RSD/CRPS type 1 has been described in children, but the incidence is much lower than in adults.

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