Entrapment syndrome of multiple nerves in graft-versus-host disease.

INTRODUCTION: Peripheral nerve entrapment syndromes are associated with hereditary neuropathy with liability to pressure palsies and a variety of rheumatic and endocrinological diseases. METHODS: We report a patient with entrapment syndromes of multiple nerves associated with chronic graft-versus-host-disease (GVHD) after allogeneic hematopoietic stem cell transplantation. Nerve ultrasound, histology, and ultrastructural changes were assessed. RESULTS: The 51-year-old man had developed severe deep dermal sclerosis due to chronic GVHD with a progressive polyneuropathy and entrapment syndromes of multiple nerves. Pre-stenotic enlargement was shown by nerve ultrasound. Histology demonstrated fibrosis of the epineurium with scarce infiltration of macrophages. Electron microscopy demonstrated alterations of the myelin sheaths and marked depletion of normal-sized myelinated nerve fibers. CONCLUSIONS: In addition to polyneuropathy, chronic GVHD can be associated with peripheral nerve entrapment syndromes and should be added to the differential diagnosis of compressive neuropathies.

Discrepancies in quantitative assessment of normal and regenerated peripheral nerve fibers between light and electron microscopy.

Quantitative estimation of myelinated nerve fiber number, together with fiber size parameters, is one of the most important tools for nerve regeneration research. In this study we used a design-based stereological method to evaluate the regenerative process in two experimental paradigms: crush injury and autograft repair. Samples were embedded in resin and morphometric counting and measurements were performed using both light and electron microscopes. Results show a significant difference in myelinated fiber number estimation between light and electron microscopes, especially after autograft repair; light microscope significantly underestimates the number of fibers because of the large number of very small axons that can be detected only in electron microscope. The analysis of the size parameters also shows a higher number of small fibers in electron microscopic analysis, especially in regenerated nerves. This comparative study shows that the integration of data obtained in light microscope with those obtained in electron microscope is necessary in revealing very small myelinated fibers that cannot be detected otherwise. Moreover, the difference in the estimation of total number of myelinated fibers between light and electron microscopes must be considered in data analysis to ensure accurate interpretation of the results.

An ultrastructural and biochemical analysis of collagen in rat peripheral nerves: the relationship between fibril diameter and mechanical properties.

Mechanical features are distributed heterogeneously within nerve tissue, with compliance increased at articulations. This study explored whether differences in stiffness between joint regions (JRs) and non-joint regions (NJRs) of rat median and sciatic nerves were related to localised variation in collagen content or fibril diameter. There was no significant difference in the amount of collagen detected by biochemical assay in JRs and NJRs of either nerve. Ultrastructural analysis showed collagen fibril diameter ranges of 20-80 nm in the endoneurium and perineurium and 30-130 nm in the epineurium. In the median nerve, but not the sciatic nerve, there were significantly smaller fibrils in JRs compared to NJRs. This corresponded to a greater number density of fibrils in JRs compared to NJRs in the epineurium and endoneurium of the median nerve. We report the presence therefore of a population of thinner collagen fibrils in the JR of the median nerve that corresponds to the location of increased compliance in this tissue, suggesting that localised variation in collagen fibril diameter contributes to the longitudinal heterogeneity of tensile properties in this nerve.

Properties of low-threshold motor axons in the human median nerve.

This study investigated the excitability and accommodative properties of low-threshold human motor axons to test whether these motor axons have greater expression of the persistent Na(+) conductance, I(NaP). Computer-controlled threshold tracking was used to study 22 single motor units and the data were compared with compound motor potentials of various amplitudes recorded in the same experimental session. Detailed comparisons were made between the single units and compound potentials that were 40% or 5% of maximal amplitude, the former because this is the compound potential size used in most threshold tracking studies of axonal excitability, the latter because this is the compound potential most likely to be composed entirely of motor axons with low thresholds to electrical recruitment. Measurements were made of the strength-duration relationship, threshold electrotonus, current-voltage relationship, recovery cycle and latent addition. The findings did not support a difference in I(NaP). Instead they pointed to greater activity of the hyperpolarization-activated inwardly rectifying current (I(h)) as the basis for low threshold to electrical recruitment in human motor axons. Computer modelling confirmed this finding, with a doubling of the hyperpolarization-activated conductance proving the best single parameter adjustment to fit the experimental data. We suggest that the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel(s) expressed on human motor axons may be active at rest and contribute to resting membrane potential.

Evaluation of diffusion tensor imaging and fiber tractography of the median nerve: preliminary results on intrasubject variability and precision of measurements.

OBJECTIVE: The purposes of this study were to determine the intrasubject side-to-side variability of quantitative and qualitative measures of diffusion tensor imaging (DTI) and fiber tractography of the median nerves and to determine the precision of quantitative measurements and fiber tractography. SUBJECTS AND METHODS: Fifteen healthy volunteers (seven men, eight women; mean age, 31.2 years) underwent DTI of both wrists with a single-shot spin-echo-based echo-planar imaging sequence (TR/TE, 7,000/103; b value 1,025 s/mm2). Postprocessing included fiber tractography and quantitative analysis of fiber length, fiber density index, fractional anisotropy, apparent diffusion coefficient, and signal-to-noise ratio. Two readers in consensus graded the quality of fiber tract images of the two wrists as equal, slightly different, or very different. Fiber tractography and all analyses were repeated after 3 weeks, and the images from the two sessions were compared. RESULTS: No statistically significant side-to-side differences in quantitative data were found (p=0.054-0.999). In all subjects, the quality of fiber tract images of the right and left median nerves was either slightly or very different. Between the initial and the second quantitative analyses, no statistically significant differences (p=0.086-0.898) were found, and the quality of fiber tract images was rated equal for nine of 15 subjects (60%) and slightly different for six of 15 subjects (40%). CONCLUSION: Preliminary results indicate that quantitative evaluation of DTI of the median nerve is precise. The absence of statistically significant intrasubject side-to-side variability in quantitative data suggests that the healthy contralateral nerve can be used as an internal control. Observed side-to-side variability in the quality of fiber tract images, however, rules out side-to-side comparisons in fiber tractography.

Employment of the mouse median nerve model for the experimental assessment of peripheral nerve regeneration.

The experimental investigation of nerve regeneration after microsurgical repair is usually carried out in rats, rather than mice, because of the larger sized peripheral nerves. Today however, the availability of genetically modified mice makes the use of this laboratory animal very intriguing for investigating nerve regeneration at a molecular level. In this study we aimed to provide a standardization of the experimental model based on microsurgical direct repair, by 12/0 suture, of the left median nerve in adult male mice. Postoperative recovery was regularly assessed by the grasping test. At day-75 postoperative, regenerated median nerve fibers were analyzed by design-based quantitative morphology and electron microscopy. Yet, sections were immuno-labelled using two axonal antibodies commonly employed for rat nerve fibers. Results indicated that functional recovery begun at day-15 and progressively increased reaching values not significantly different from normal by day-50. Quantitative morphology showed that, at day-75, the number of regenerated nerve fibers was not significantly different in comparison to controls. In contrast, differences were detected in fiber density, mean axon and fiber diameter and myelin thickness which were all significantly lower than controls. Immunohistochemistry showed that axonal markers commonly used for rat nerves studies are effective also for mouse nerves. Similar to the rat, the mouse median nerve model is superior to sciatic nerve model for the minimal impact on animal well-being and the effectiveness of the grasping test for motor function evaluation. The main limitation is the small nerve size which requires advanced microsurgical skills for performing 12/0 epineurial suturing.

High-resolution sonography of the palmar cutaneous branch of the median nerve.

OBJECTIVE: The aim of this study was to describe the potential value of high-resolution sonography for evaluation of the palmar cutaneous branch of the median nerve (MN). SUBJECTS AND METHODS: The volar wrists of 12 healthy volunteers and 22 consecutive patients with sensory deficit in the palmar triangle and thenar eminence suggesting neuropathy of the palmar cutaneous branch of the MN were examined with high-frequency sonography. Nine patients underwent carpal tunnel release, five had a history of penetrating trauma, six had symptoms suggesting concurrent carpal tunnel syndrome, one received surgery for palmaris tendon transfer, and one underwent resection of a ventral carpal ganglion cyst. Correlative 1.5-T MRI was performed in six patients. RESULTS: In 83% of the healthy volunteers, 17-5-MHz sonography was able to identify the palmar cutaneous branch of the MN from its origin down to slightly distal to the wrist crease. In the patient group, sonography allowed detection of nerve abnormalities in 55% of the cases. Focal hypoechoic swelling of the nerve at the fascial crossing was observed in patients who had either concurrent carpal tunnel syndrome (four cases) or previous carpal tunnel release (three cases). Sonography performed after a penetrating trauma revealed nerve encasement by scar tissue (two cases) or complete transection of the nerve ending in a terminal neuroma (one case). Nerve transection secondary to resection of a ventral carpal ganglion cyst (one case) or to carpal tunnel release (one case) was also observed. CONCLUSION: Sonography can identify the palmar cutaneous branch of the MN and characterize its abnormalities, providing unique information about this small nerve branch.

Long nerve gaps limit the regenerative potential of bioartificial nerve conduits filled with Schwann cells.

PURPOSE: Recently we successfully used a conduit of epsilon-caprolactone-co-trimethylene carbonate filled with Schwann cells (SC) across a 20 mm gap in a rat median nerve. In this study we applied the tubes with SC across a 40 mm gap in order to analyse the regenerative potential of the tubes in long nerve defects. METHODS: To augment the nerve defect a cross-chest procedure was used and the tubes were implanted with injected isogeneic SCs inside (group 3). Both ulnar nerves were used for a 40 mm autograft (group 2). For control group non-operated animals were used (group 1). The grasping test, histology (S-100, PAM), electrophysiology, and the muscle weight were used to assess regeneration. RESULTS: After 12 months, grasping was seen only in three animals of group 3 (3.6 g [95% CI: 0 to 7.6 g]). However, in group 2 all rats had a partial functional regeneration (42.8 g [95% CI: 39.1 to 46.6 g]). The grasping force of the non-operated animals (group 1) was 240.9 g [95% CI: 237.2 to 244.7 g] at the time. Histology from group 3 confirmed an irregular arrangement of fibres in contrast to more organized structures in group 2. Electrophysiology in group 3 displayed potentials only in the three animals with functional regeneration. In group 2 all animals exhibited potentials. A significant decrease of muscle weight was observed in groups 2 and 3, most prominent in the latter. CONCLUSION: Regeneration was not successful across the 40 mm gap using the applied tube in combination with SC. For future experiments further consideration should be taken in optimizing the cellular and material components that are critical for a successful application to overcome very large nerve gaps.

[Impact of loss of sympathetic innervation on peripheral nerve regeneration: an experimental study with rats].

OBJECTIVE: To investigate the impact of loss of sympathetic innervation on peripheral nerve regeneration. METHODS: Thirty-two SD rats underwent resection of the right middle cervical ganglion and excision and re-anastomosis of bilateral medium nerve, and then were randomly divided into 4 equal groups to undergo the following experiments. One, 2, 3, and 4 weeks later the sensory nerve action potentials (SNAPs) of bilateral medium nerves 5 mm from the anastomotic stoma and the compound muscle action potentials (CMAPs) of bilateral superficial digital flexor muscles were measured with stimulating and recording electrodes. Specimens of the distal part of bilateral medium nerves 5 mm from the anastomotic stoma were collected to calculate the number of modulated fibers by electron microscopy. The tendons of bilateral superior digital flexor muscles were cut ant the wrist, isolated to the terminal points, ligated, and connected to a sensor so as to record the maximum contraction power. The superior digital flexor muscle was completely resected to be weighted. RESULTS: CMAP failed to be recorded 1 week later. The wave amplitude of the nerve at the affected side increased along with time, however, the CMAP wave amplitudes of the affected side were all significantly lower than those of the healthy side (all P < 0.05). The SNAP wave amplitudes of the medium nerve of both sides increased along with the time. The SNAP levels 4 and 8 weeks later of the affected side were both lower than those of the healthy side (both P < 0.05). The number of modulated fibers of the medium nerve increased along with the time, however, the number of the affected side were significantly lower than those of the healthy side (all P < 0.05). Electron microscopy showed degeneration of medulla in bilateral medium nerves 1 week later, and newborn modulated fibers began to be seen since 2 weeks later. However, there were a greater number and more complete structure in the healthy side in comparison with the affected side. The wet weights of bilateral superior digital flexor muscles decreased 2 weeks later and then began to increase gradually. However, the wet weight 4 and 8 weeks later were significantly greater in the healthy side then in the affected side (both P < 0.05). CONCLUSION: Resection of sympathetic nerve is advantageous on nerve regeneration.

A histological analysis of human median and ulnar nerves following implantation of Utah slanted electrode arrays.

For decades, epineurial electrodes have been used in clinical therapies involving the stimulation of peripheral nerves. However, next generation peripheral nerve interfaces for applications such as neuroprosthetics would benefit from an increased ability to selectively stimulate and record from nerve tissue. This increased selectivity may require the use of more invasive devices, such as the Utah Slanted Electrode Array (USEA). Previous research with USEAs has described the histological response to the implantation of these devices in cats and rats; however, no such data has been presented in humans. Therefore, we describe here the degree of penetration and foreign body reaction to USEAs after a four-week implantation period in human median and ulnar nerves. We found that current array designs penetrate a relatively small percentage of the available endoneurial tissue in these large nerves. When electrode tips were located within the endoneurial tissue, labels for axons and myelin were found in close proximity to electrodes. Consistent with other reports, we found activated macrophages attached to explanted devices, as well as within the tissue surrounding the implantation site. Despite this inflammatory response, devices were able to successfully record single- or multi-unit action potentials and elicit sensory percepts. However, modifying device design to allow for greater nerve penetration, as well as mitigating the inflammatory response to such devices, would likely increase device performance and should be investigated in future research.

Localization and changes of intraneural inflammatory cytokines and inducible-nitric oxide induced by mechanical compression.

STUDY DESIGN: Investigation of intraneural inflammation induced by mechanical compression. OBJECTIVES: In order to investigate the mechanism of neuropathy, this study used a median nerve compression model in dogs. Immunohistochemistry was used to examine the localization and changes of inflammatory cytokines and nitric oxide (NO). SUMMARY OF BACKGROUND DATA: The manifestation of pain at sites of inflammation has a close relationship with the release of mediators from macrophages such as interleulin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha), as well as with NO. However, the mediators involved in inflammation of nerve due to mechanical compression remain almost unknown. METHODS: In this study, the median nerve of dogs was compressed with a clip for three weeks to observe the changes caused by compression. Immunohistochemistry was done by the avidin-biotin-peroxidase complex method to observe the changes of T cells (CD45) and macrophages (Mac-1) after compression. Antibodies against IL-1beta, TNF-alpha, and inducible nitric oxide synthesis (i-NOS) were used to examine the localization and changes of these mediators caused by nerve compression. RESULTS: In control animals, resident T cells were detected, but there were no macrophages. IL-1beta was positive in the Schwann cells and vascular endothelial cells. However, no cells showed TNF-alpha or i-NOS positively. After nerve compression, numerous T cells and macrophages appeared among the demyelinized nerve fibers. The macrophages were positive for IL-1beta, TNF-alpha and i-NOS. CONCLUSION: Inflammatory cytokines and NO may be involved in intraneural inflammatory changes arising from mechanical compression. Such mediators may be of importance in the manifestation of neuropathy.

Renaut bodies contain elastic fiber components.

Renaut bodies (RB) are fusiform endoneurial structures preferentially found at sites of nerve entrapment, often occupying more than 30% of the cross-sectional area of a nerve fascicle. Their composition and significance, however, are still incompletely understood. In this study, further evidence for the link between the appearance of RB and nerve entrapment is presented. Reanaut bodies were already found at the age of 1 year in the median nerve at the level of the wrist, i.e. in the carpal tunnel, a possible site of entrapment. Here, their number increased with age. Renaut bodies were absent, however, in fetal nerves at this site. Many of the cells in RB resembled perineurial cells or pericytes. They were stained with antibodies against vimentin and epithelial membrane antigen and were partially covered by a basal lamina reactive with antibodies against collagen IV, laminin, and s-laminin. Focally accumulated filaments and bundles of 30-40 nm collagen fibrils were major extracellular components of RB. The diameter of the filaments (8-12 nm) corresponded to the size of the microfibril, i.e. the oxytalan component of elastic fibers. Renaut bodies were intensely stained with antibodies against these microfibrils and several types of collagen glycoproteins. On the basis of these results, we conclude that RB are composed of cells that show perineurial differentiation. These cells produce an extracellular matrix highly enriched in elastic fiber components.

Fast axonal transport in amyotrophic lateral sclerosis: an intra-axonal organelle traffic analysis.

Fast transport of intra-axonal organelles was studied in motor nerve from amyotrophic lateral sclerosis (ALS) patients. Organelle traffic in ALS nerves demonstrated a significant increase in anterograde mean speed, while retrograde mean speed was decreased compared with that of controls. Retrograde traffic density (organelles per unit time) was also significantly decreased in the ALS specimens. Anterograde transport machinery is therefore intact and may be responding to the increased physiologic demand of larger motor units. Diminished retrograde speed and organelle traffic density are consistent with a defect in retrograde transport and could impair communication between axon terminals and perikarya.

Maximal regeneration distance. How far can a peripheral axon regenerate?

Peripheral nerves of the fore- and hindlimbs of 20 rats were induced to regenerate over double and triple of their original lengths through consecutive orthograde and retrograde (zigzag) anastomoses along parallel nerves of the same limb. Morphological changes were followed on longitudinal sections of the whole-mount composite nerves by several histological techniques. Regeneration regularly took place along this pathway. The regenerated axonal segments were intensively remyelinated, demonstrating the capacity of the spinal neurons to produce and maintain disproportionately long axonal processes. These observations may be relevant for reconstructive neurosurgery when very long peripheral nerve gaps have to be bridged.

Mycobacteria in nerve trunks of long-term treated leprosy patients.

Mycobacteria were present in 4 out of 8 mixed peripheral nerve trunks from patients (3 BT and 1 BL) treated with DDS and/or MDT for periods ranging from 21 months to 8 years. Most of the bacilli appeared to be 'whole'. Nerve destruction with areas of granulomatous infiltration appeared more active than expected. Possible reasons for a continued presence of bacilli in treated nerves and its implications in 'relapse' are discussed.

Hypertrophic mononeuropathy. A report of two cases and review of the literature.

Two cases of hypertrophic mononeuropathy were studied. This entity is characterized grossly by focal enlargement of a single peripheral nerve, and microscopically by loss of nerve fibers, fibrosis, and formation of numerous onion bulbs. Our cases were diagnosed by exploratory surgery, biopsy, and light microscopy. Electron microscopic evaluation was performed in one case. Recognition of this entity by the surgical pathologist is important, so that it can be distinguished from generalized forms of onion bulb neuropathies, most of which give a much less favorable long-term prognosis. Hypertrophic mononeuropathy has usually resulted in irreversible local neurologic deficit but, unlike the polyneuropathies, in all the previously reported cases (as well as in our two cases to date) it has remained a localized process.

Cement burn of the sciatic nerve.

We present the case of a 63-year-old woman who sustained an acrylic cement burn of the sciatic nerve at hip replacement. She was treated by resection of the damaged segment and grafting. Electron microscopy showed that the nerve was nearly normal 1 cm from the cement margin indicating that this is a safe level for resection.

Polarization of nerve regeneration (electrotaxis).

Regeneration of both median nerves was studied in the rat in three different experimental models of centrocentral anastomosis through an interposed segment of pre-degenerated tibial nerve after denervation by spinal root transection. Different patterns of regeneration were observed in the anastomoses. These patterns suggest a bio-electrical polarity related to neuronal function. The present experimental model appears to offer a new opportunity to study neuronal regeneration under the influence of defined bioelectrical conditions.

Effects of cyclosporin A and predegeneration on survival and regeneration of peripheral nerve allografts in rabbits.

Axonal regeneration across 64 median nerve grafts in 34 rabbits was studied histologically to determine the optimal conditions for nerve allografting. Axonal regeneration across allografts in cyclosporin A-treated animals was satisfactory, but it occurred more slowly and with more inflammation and fibrosis than in autografts. Without immunosuppression, fresh allografts were rejected. However, in immunocompetent hosts, allografts rendered less immunogenic by predegeneration were not rejected, and axonal regeneration occurred. The combination of cyclosporin A and nerve graft predegeneration produced the most substantial axonal regeneration, comparable to autografts. The observations suggest that nerve allograft survival may be optimally effected by cyclosporin A treatment coupled with reduction in the immunogenicity of the grafts, such as by predegeneration.