Andrea Trescot
Complex Regional Pain Syndrome (CRPS) has been a very difficult pain syndrome to diagnose and treat, primarily because the criteria are clinical, and the treatments primarily symptomatic. Most of the research on CRPS has focused on the central sensitization, but there has been a recent recognition of the peripheral disease mechanisms that may trigger and maintain CRPS. The onset of CRPS is usually triggered by an injury (which may have been “trivial”) with resultant pain, sensory dysfunction, edema, and trophic changes that can spread to other areas of the body. Classically, CRPS has been divided into Type I (without a nerve lesion) and Type II (with a documented nerve injury), and has been regarded as primarily a disorder of the central nervous system mediated by sympathetic dysfunction. Type I is much more common, and may reflect an unrecognized small peripheral nerve entrapment. The lack of diagnosis and therefore treatment of an underlying pathology (peripheral nerve entrapment) may have contributed to the lack of consistent response to a wide variety of treatments. This lecture will focus on the potential mechanism of injury (peripheral nerve entrapment), leading to the initiation and perpetuation of CRPS. Several clinical scenarios will be presented, illustrating these mechanisms, describing the diagnostic injections as well as the cryoanalgesia techniques for treatment.
Introduction-
During the American Civil War, Mitchell noted that some soldiers developed a particularly painful state after bullet injuries. In his reports, he described soldiers who experienced burning pain that never affected the trunk, rarely affected the thighs and arms, but often involved the legs and forearms, and mainly involved the hands and feet. The patients described burning pain, which became intensely hyperalgesic. At some point, they avoided even contact with the air, which now we know as allodynia. As time went by, the patient’s face showed evidence of suffering, they developed sleep disturbances, and finally, they became hysterical. A few years later, Mitchell coined the term “causalgia” (from Greek kausos fever + algia pain) to describe this condition.
Since these early reports, many terms such as Sudeck’s atrophy, sympathalgia and reflex sympathetic dystrophy have been used to describe this clinical scenario. In 1994, the Committee of Classification of Chronic Pain of the International Association for the Study of Pain (IASP) coined the term “Complex Regional Pain Syndrome” (CRPS) as a definitive nomenclature, with its typical subtypes: CRPS type I (where there is no obvious nerve damage) and CRPS type II (where there is identifiable nerve damage.
Symptoms of CRPS-
Symptoms of CRPS-I (which used to be called reflex sympathetic dystrophy) include “burning” pain (a term that usually used to describe superficial structures) and “aching” pain (describing pain in the deep tissues) as well as a variety of stimulus-evoked pain sensations, including hyperalgesia and allodynia (with mechanical, cold, and sometimes heat sensitivity) . Other symptoms include vasomotor and sudomotor dysregulation; trophic changes in the skin, hair, nails, and bone; and dystonia or other motor abnormalities . The clinical presentation of CRPS-II (which used to be called causalgia) is the same in all respects, except that a verifiable nerve injury is present.
Coderre and Bennett have developed an animal model of chronic post-ischemia pain that creates CRPS-I-like symptoms. These finding, coupled with recent histological and animal data, suggest that some form of initial nerve trauma is “an important trigger for the cascade of events leading to CRPS” Therefore, the distinction between the pathogenesis of CRPS-I (“non-nerve”) and that of CRPS-II (“defined nerve”) may be a matter of degree and not of mechanism.
Risk Factors-
There are several studies that tried to identify patients at risk for developing CRPS. Geertzen et al. in a case-control study, found that 79.2% of patients with CRPS were able to relate a major stressful event at least 3 months prior to the disease versus 21.4% of the control group. Dilek et al. also showed that high anxiety was correlated with a higher incidence of CRPS after distal radial fracture. However, others have failed to link anxiety and stress to CRPS .
It is well accepted that high levels of pain in the early phases of trauma is strongly related to higher incidence of CRPS, suggesting a central sensitization as a background for the disease ,Female gender can be considered a risk factor for CRPS and, since there is a higher incidence in older patients, the postmenopausal status is also related higher incidence of CRPS, although this association could be an epiphenomena linked to higher incidence of fractures and others traumas in this population. However, the common factor in many of these risks may be nerve entrapment.
Treatment-
Treatment of nerve entrapments requires first the right diagnosis, which usually involves a diagnostic injection, using landmarks, ultrasound (US), or fluoroscopy . The injection of local anesthetic provides the anesthesia, as well as local disruption of the sympathetic stimulation; depot steroids are usually also injected to address the inflammation. If there is only temporary relief, the use of hydrodissection (fluid is injected around the nerve under US guidance to lyse the adhesions around the nerve) may be of use. Cryoneuroablation, which freezes the nerve but leaves the myelin sheath intact, is a technique of nerve destruction that can be safely used on large, myelinated nerves . Peripheral nerve stimulation and surgical release might also offer relief.
-The radial nerve arises from the posterior cord of the brachial plexus, spirals around the humerus, and then descends down the humerus to the elbow. At the elbow, the radial nerve divides into a superficial and deep branch. The superficial branch (SRN) travels under the brachioradialis muscle (BR) and then travels superficially along the distal radial forearm to the thumb and dorsum of the hand
- Splinting, changing work ergonomics, and diagnostic/therapeutic injections are first line treatments. In one series, 71% of 29 patients had excellent or good pain relief after non-operative interventions . If SRN injections give only temporary relief, cryoneuroablation could be indicated. Davies et al. described 6 patients treated with cryoneuroablation via open visualization of the nerve or neuroma . Patients were followed for a mean of 11 months; all reported good to excellent relief, and every one returned to figure
Conclusion-
Peripheral nerve entrapments can mimic CRPS; more importantly, these unrecognized (and under-recognized) nerve entrapments might actually be the explanation for CRPS. the excellence between CRPS type I and II won't be “no nerve injury” versus “nerve injury”, but one among “unrecognized nerve injury” versus “recognized nerve injury”. the main target of treatment should then shift to resolving the nerve compression instead of just addressing the sympathetic system.
References-
1.Gross CG (1998) Claude Bernard and the consistancy of the internal environment. The Neuroscientist 4: 380-385.
2.Mitchell SW, Morehouse GR, Keen WW (1864) Gunshot Wounds and Other Injuries of Nerves. Philadelphia: J. B. Lippincott & Co.
3.Mitchell SW (1872) Injuries of the Nerves and Their Consequences. Philadelphia: J. B. Lippincott & Co.
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