Edited by: Alexej Verkhratsky, University of Manchester, United Kingdom
Reviewed by: Ada Maria Tata, Sapienza Università di Roma, Italy; Wenquan Zou, Case Western Reserve University, United States
This article was submitted to Neurodegeneration, a section of the journal Frontiers in Neuroscience
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Complex regional pain syndrome (CRPS) is a collection of painful conditions that are characterized by a continuing regional pain, disproportionate to the usual course of any known trauma or other lesion (Harden et al.,
The pathophysiology of CRPS remains elusive, and consequently treatment options are still inadequate. Several pathophysiological hypotheses have been suggested: Central nervous system (CNS) reorganization (Maihöfner et al.,
Treatment strategies are based on addressing individual symptoms with known existing therapies to alleviate burden of disease (Perez et al.,
We describe a rare case of CRPS leading to forearm amputation and the subsequent histopathological study of peripheral nerve tissue from the amputate. Our results demonstrate a selective large fiber degeneration which is a novel finding and in keeping with current knowledge on CRPS pathophysiology.
This study was carried out in accordance with the recommendations of the National Research Ethics Committee, UK with written informed consent from the subject, in accordance with the Declaration of Helsinki. The protocol was approved by the National Research Ethics Committee, UK (NRES 13/SC/0499).
The patient in our study was a 35-year-old female who sustained a low voltage alternating current (110–380 V) electrical injury to her left hand. Left forearm pain, paraesthesia and bluish skin discoloration were features from initial presentation. In the 3 weeks following injury, she developed progressive patchy paraesthesia and dysaesthesia predominantly in the median nerve distribution of the affected hand. An ultrasound showed a normal appearance of the median nerve and of structures within the carpal tunnel and distal forearm. Acute carpal tunnel syndrome was suspected as being responsible for at least part of the presenting symptoms. With the possibility of secondary median nerve compression related to the injury, a carpal tunnel release procedure was undertaken at 3 weeks post injury. The median nerve appearance was macroscopically normal. Postoperatively, some paraesthesia in the territory of the median nerve improved but forearm pain persisted.
From 1 month post injury, the patient's disease continued to progress; all movements and sensory stimulants to the affected hand were grossly intolerable and a diagnosis of CRPS was made. The diagnosis was made based on the patient fulfilling the Budapest criteria, as shown in Table
Diagnosis of Complex Regional Pain Syndrome in the studied patient.
The patient has continuing pain which is disproportionate to the inciting event | Pain was of early onset, progressive, unremitting despite all targeted interventions and disproportionate |
The patient has at least one sign in two or more of the following categories: sensory, vasomotor, sudomotor, motor | Allodynia and hyperalgesia, decreased range of motion in wrist, fingers and thumb despite intensive hand therapy inputs, major trophic changes including skin changes and development of raw areas |
The patient reports at least one symptom in three or more of the same categories: sensory, vasomotor, sudomotor, motor | Altered sensibility to light touch, joint movement, and experiencing magnified pain stimulus to pinprick. Reported differences in color of the two forelimbs, intractable stiffness despite full compliance with physiotherapy regimen |
No other diagnosis can better explain the signs and symptoms | No alternative diagnosis was found (and she also came under care of the regional pain clinic who concurred with diagnosis of CRPS) |
From 1 to 10 months post-injury, the patient received specialist therapy and pain management including pharmacological agents such as gabapentin, paracetamol, ibuprofen, tramadol, amitriptyline, ketamine, pamidronate infusions, lidocaine plasters, nabiximols, and capsaicin cream, which all failed to give relief. Supraclavicular catheter blocks, transcutaneous electrical nerve stimulation (TENS), and hand physiotherapy were also ineffective. At 9 months post injury, the patient was experiencing spontaneous skin breakdown with weeping, cellulitis and was hospitalized as a result of these infections. She was unable to clean her skin due to excessive pain. By the end of this period the patient had developed a functional loss of the limb. The patient requested an amputation which was ultimately supported by the multidisciplinary team consisting of plastic surgeons and pain anesthetists. The potential for control of pain was a secondary aim, as the impact of amputation on pain could not be fully predicted.
Ten months post-injury, the patient underwent a below elbow amputation at the level of the proximal third of the forearm, with a dorsally based flap of intact skin used to resurface the residuum. Nine months post-amputation the patient has not had any recurrence of CRPS at the amputation site, which is fully healed. She has had a dramatic response in terms of relief of CRPS symptoms. She has regained her quality of life and is wearing a cosmetic artificial arm prosthesis, with plans for her to progress to use of a myoelectric prosthesis.
Nerve samples were obtained from the median, ulnar and radial nerves at the level of the distal and proximal thirds of forearm, as shown in Figure
Diagram showing the level of forearm amputation as well as the levels at which the proximal and distal nerve samples were taken. Original biopsies were 3 cm long, which were further dissected during sample processing, fixation, and embedding for electron microscopy.
Transmission electron microscopy (TEM) images were obtained using a FEI Tecnai12 BioTwin microscope and images were taken using a Gatan Orius sc1000 digital Camera available at the Faculty of Biology, Medicine and Health Core Facilities, University of Manchester. For each nerve (distal and proximal samples combined), 18–20 images at x440 magnification were taken in different areas of the nerve fascicles chosen at random. Images were analyzed with ImageJ 64 imaging software (National Institutes of Health NIH, Bethesda, MD, USA). Nerve fibers were categorized according to status (healthy vs. degenerative) based on histological appearances. Histological features of fiber degeneration included distortion of myelin sheaths, entire fiber degeneration, degenerating Remak bundles, and denervated Schwann cell bands (unmyelinated axon loss). Nerve fiber size was measured according to maximum Feret diameter including myelin. Individual nerve fibers were measured and categorized according to the nerve fiber type classification, originally described by Gasser (
Nerve fiber classification.
Aα | 12–20 | Somatomotor, proprioception |
Aβ | 5–12 | Touch, pressure |
Aγ | 3–6 | Muscle spindle |
Aδ | 2–5 | Pain and temperature |
B | <3 | Preganglionic autonomic |
C | 0.4–1.2 (unmyelinated) | Postganglionic autonomic, pain, temperature |
After collection on glass slides, light microscopy semi-thin sections were further stained with toluidine blue 0.5% w/v for 60 s on a warm hot plate before mounting and analysis. Images were acquired with an Olympus IX51 inverted microscope (Olympus, Southend-on-Sea, UK). Light microscopy images were also analyzed with ImageJ 64 software. A total of 4 nerve fascicles for each nerve (2 distal and 2 proximal) were analyzed and myelinated nerve densities calculated and compared to findings from the literature.
Statistical analysis comparing healthy and degenerative nerve fiber sizes was conducted using unpaired
Routine hospital histology of skin, muscle, fat, and forearm nerve specimens showed only mild superficial chronic inflammation in the superficial dermis and several foci of calcified material in the muscle.
A total of
Light microscopy of a nerve fascicle from the distal ulnar nerve sample (bar represents 50 μm). The perineurium and endoneurium are visualized. The circle indicates a cluster of healthy myelinated axons. Arrows indicate examples of degenerating fibers. Degenerative features included myelin breakdown and collapsed nerve fibers. Stain: toluidine blue.
Median myelinated fiber densities expressed (fibers/mm2).
Nerve | This study ( |
CRPS nerves (Geertzen et al., |
Healthy nerves (O'Sullivan and Swallow, |
Ulnar | 6,208 (5,380–7,950) | 5,400 (3,670–8,179) | – |
Median | 8,017 (5,652–9,656) | 6,920 (5,662–8,284) | – |
Radial | 6,950 (6,443–8,490) | 4,823 (4,194–7,025) | 7,120 (5,410–10,020) |
All nerve samples showed evidence of selective myelinated nerve fiber degeneration using electron microscopy (Figures
Transmission electron microscopy (TEM) images of proximal ulnar
Histogram showing the percentage of healthy and degenerative myelinated nerve fibers in our study. Forty-seven to fifty-four percent of myelinated nerve fibers showed evidence of degeneration.
A total of 796 nerve fibers for radial, ulnar, and median nerves were individually measured. Degenerating myelinated nerve fibers were significantly larger than healthy nerve fibers in all nerve samples (
Mean myelinated fiber sizes in our study (μm).
Healthy | 7.0 (SD 3.2) | 6.3 (SD 3.0) | 7.1 (SD 2.8) |
Degenerating | 12.3 (SD 3.9) | 13.6 (SD 4.9) | 12.6 (SD 4.4) |
p-value | <0.05 | <0.05 | <0.05 |
Nerve fiber distribution according to size (μm).
All nerve samples showed evidence of unmyelinated nerve fiber degeneration. Histological features of unmyelinated nerve fiber degeneration included degenerating Remak Bundles, and denervated Schwann cell bands (unmyelinated axon loss; Figures
Absolute counts of healthy and degenerating Remak bundles (groups of small unmyelinated C fibers) in all nerves in our study.
Median | 127 | 25 |
Ulnar | 129 | 26 |
Radial | 72 | 55 |
We describe ultrastructural changes in nerve fibers in the context of a rare case of CRPS requiring amputation of the distal forelimb. Results indicate that degeneration occurred selectively in large myelinated and small unmyelinated nerve fibers as compared to the medium and small myelinated nerve fibers, which were conserved. This has potential implications for the understanding of the pathogenesis of CRPS.
This study is believed to be the first showing ultrastructural images of large fiber (Aα) degeneration in CRPS using TEM. This was further corroborated by our light microscopy images showing large nerve fiber degeneration in all nerve fascicles. Our results are in line with a recent study of 15 severe CRPS patients who underwent amputation and where histological evidence of peripheral nerve pathology was found on light microscopy in radial, median, ulnar, tibial, and sural nerves (Geertzen et al.,
We propose that degeneration of Aα fibers may lead to an imbalance in nerve signaling if the majority of axonal messaging goes through the smaller healthy Aδ fibers, which may inappropriately trigger pain. As previously stated Aδ fibers are myelinated fibers that transmit pain and temperature and their hypersensitivity will cause symptoms of allodynia to light touch or temperature, or hyperalgesia. The concept of surviving fibers inappropriately firing when neighboring fibers are degenerating has long been established in neuropathic pain (Oaklander and Fields,
Furthermore, we postulate that large Aα fiber degeneration contributes to motor symptoms in CRPS. As previously stated Aα fibers have a somatomotor function in the peripheral nervous system. Our patient suffered from motor weakness as CRPS progressed, and our histological findings are in keeping with this clinical picture. Movement disorders such as bradykinesia and dystonia affect around 25% of patients with CRPS (van Hilten,
Of interest, Geertzen et al. (
Importantly this study has also demonstrated small unmyelinated C fiber pathology in upper limb CRPS nerves. This had previously been shown in 4 out of 8 patients in lower limb sural nerves (van der Laan et al.,
Radial nerve myelinated fiber densities in our study and healthy radial nerve densities in O'Sullivan et al. were similar, particularly when comparing the medians. Our results (Table
Limitations of this study are the sample size (
Low voltage electrical injuries (<1,000 V) tend to not produce any neurological sequelae and rarely require clinical follow up or hospital admission. For this reason we know little about peripheral nerve changes following low voltage electrical nerve injury. It is unlikely our patient's condition was caused by low voltage electrical injury alone, without an additional pathological process such as that of CRPS. Electrical injury has been known to be a trigger for CRPS (Cohen,
It is possible that our histological findings were due to chronic disuse of the upper limb alone, as our patient's nerves were examined at 10 months post injury. Immobilization and disuse are known factors contributing to CRPS, with one study reporting up to 47% of all CRPS sufferers as having a history of medically imposed immobilization (Allen et al.,
In summary, we demonstrate selective large myelinated fiber degeneration in the upper limb peripheral nerves of a patient with CRPS. We recognize the limitations of a single patient study and lack of control nerve examination; however, our findings have been placed into the context of all previously published literature and present an important hypothesis on the peripheral nerve pathophysiology of CRPS.
All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The handling Editor declared a shared affiliation, though no other collaboration, with several of the authors AY, AF, and AR.
The authors would like to acknowledge Professor Giorgio Terenghi for his invaluable contribution and expertise in histology interpretation. The authors also acknowledge the assistance of Samantha Forbes (Faculty of Biology, Medicine and Health, University of Manchester) for the embedding of nerve samples and acquisition of electron microscopy images.
Complex regional pain syndrome
transcutaneous electrical nerve stimulation
transmission electron microscopy.