Reflex sympathetic dystrophy syndrome (RSDS) has been recognized since the Civil War when it was called causalgia, a name chosen to describe intense, burning extremity pain after an injury. Since then, RSDS has had a number of name changes. Bonica coined the term reflex sympathetic dystrophy in 1953. The American Association of Hand Surgery proposed changing the name to sympathetic maintained pain syndrome. A consensus expert panel recommended a change to complex regional pain syndrome (CRPS). However, although many clinicians still use the term RSDS, the terms currently in favor are complex regional pain syndrome I (the equivalent of RSD) and complex regional pain syndrome II, also known as causalgia.
CRPS/RSDS has readily identifiable signs and symptoms and is treatable if recognized early; however, the syndrome may become disabling if unrecognized.  Emergency physicians are frequently in a position to identify the problem and may play a significant role in minimizing impact of this common entity.
No single hypothesis explains all features of reflex sympathetic dystrophy syndrome (RSDS). Schwartzman stated that a common mechanism may be injury to central or peripheral neural tissue.  Roberts proposed that sympathetic pain results from tonic activity in myelinated mechanoreceptor afferents. Input causes tonic firing in neurons that are part of a nociceptive pathway. Campbell et al propose a hypothesis that places the primary abnormality in the peripheral nervous system.  More recent articles agree that the cause is still unknown.  Recent interest has focused on an immune-mediated mechanism. 
Most authors now agree that complex regional pain syndrome (CRPS) is a neurologic disorder affecting central and peripheral nervous systems. [6, 7] Mechanisms include peripheral and central sensitization, inflammation, altered sympathetic and catecholaminergic function, altered somatosensory representation in the brain, genetic factors, and psychophysiologic interactions. [7, 8]
Other etiologic possibilities have been suggested. German research has noted the association between elevated levels of soluble tumor necrosis factor receptor 1 (sTNF-R1) and enhanced tumor necrosis factor-alpha activity in patients with polyneuropathy with allodynia.  Other German researchers have described autoantibodies in patients with CRPS, especially CRPS type 2. 
Harvard researchers Oaklander and Fields have proposed that distal degeneration of small-diameter peripheral axons may be responsible for the pain, vasomotor instability, edema, osteopenia, and skin hypersensitivity of CRPS-1. 
The recent association between the use of ACE inhibitors and CRPS has caused some to consider a neuroinflammatory pathogenesis. 
Recent research has demonstrated cortical changes, suggesting a possible role in pathophysiology. 
All agree that, regardless of the mechanism, the patient experiences intense, burning pain in one or more extremities.
CRPS occurs in approximately 1-15% of peripheral nerve injury cases. Schwartzman states that CRPS usually occurs secondary to fractures, sprains, and trivial soft tissue injury.  The incidence after fractures and contusions ranges from 10-30%. While some cases are associated with an identifiable nerve injury, many are not. Even "microtrauma" as might occur with an immunization may be responsible. The upper extremities are more likely to be involved than the lower. Entities that have led to RSDS include the following:
Operative procedures (eg, carpal tunnel release)
Minor extremity injury
In and of itself, the disease is not fatal. Morbidity of RSDS is associated with disease progress through a series of stages (see Physical).
Schwartzman et al recently reviewed questionnaires from 656 patients with CRPS. Once patients had experienced symptoms for more than one year, the majority of signs and symptoms were developed. No one reported spontaneous remission of symptoms. 
The 2009 questionnaire review by Schwartzman et al showed that, in the population he studied, the overwhelming majority (96%) were white and 80% were female. 
Stanton-Hicks and others note that women predominate in a range of 60-80% of cases. 
Persons of all ages are affected. Stanton-Hicks reports that in contrast to adults, 90% of pediatric cases occur in female children aged 8-16 years, with the youngest being 3 years. That author and others report that CRPS is treated most effectively in pediatric patients, with a remission rate of 97%. [16, 17]
An Israeli group suggested that CRPS in children and adolescents is underdiagnosed. They emphasize the importance of early recognition and multidisciplinary treatment. 
Several have looked into the possibility that there may be an increased risk of CRPS development in siblings. de Rooij et al showed that, although the overall risk is not increased, the risk in siblings younger than 50 years is significantly increased. [19, 20]
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