Peripheral nervous system involvement in chronic spinal cord injury

Magnetic resonance neurography in spinal cord injury: Imaging findings and clinical significance

BACKGROUND AND PURPOSE

It is unknown whether changes to the peripheral nervous system following spinal cord injury (SCI) are relevant for functional recovery or the development of neuropathic pain below the level of injury. Magnetic resonance neurography (MRN) at 3 T allows detection and localization of structural and functional nerve damage. This study aimed to combine MRN and clinical assessments in individuals with chronic SCI and nondisabled controls.

METHODS

Twenty participants with chronic SCI and 20 controls matched for gender, age, and body mass index underwent MRN of the L5 dorsal root ganglia (DRG) and the sciatic nerve. DRG volume, sciatic nerve mean cross-sectional area (CSA), fascicular lesion load, and fractional anisotropy (FA), a marker for functional nerve integrity, were calculated. Results were correlated with clinical assessments and nerve conduction studies.

RESULTS

Sciatic nerve CSA and lesion load were higher (21.29 ± 5.82 mm2 vs. 14.08 ± 4.62 mm2 , p < 0.001; and 8.70 ± 7.47% vs. 3.60 ± 2.45%, p < 0.001) in individuals with SCI compared to controls, whereas FA was lower (0.55 ± 0.11 vs. 0.63 ± 0.08, p = 0.022). DRG volumes were larger in individuals with SCI who suffered from neuropathic pain compared to those without neuropathic pain (223.7 ± 53.08 mm3 vs. 159.7 ± 55.66 mm3 , p = 0.043). Sciatic MRN parameters correlated with electrophysiological results but did not correlate with the extent of myelopathy or clinical severity of SCI.

CONCLUSIONS

Individuals with chronic SCI are subject to a decline of structural peripheral nerve integrity that may occur independently from the clinical severity of SCI. Larger volumes of DRG in SCI with neuropathic pain support existing evidence from animal studies on SCI-related neuropathic pain.

A comprehensive look at the psychoneuroimmunoendocrinology of spinal cord injury and its progression: mechanisms and clinical opportunities

Spinal cord injury (SCI) is a devastating and disabling medical condition generally caused by a traumatic event (primary injury). This initial trauma is accompanied by a set of biological mechanisms directed to ameliorate neural damage but also exacerbate initial damage (secondary injury). The alterations that occur in the spinal cord have not only local but also systemic consequences and virtually all organs and tissues of the body incur important changes after SCI, explaining the progression and detrimental consequences related to this condition. Psychoneuroimmunoendocrinology (PNIE) is a growing area of research aiming to integrate and explore the interactions among the different systems that compose the human organism, considering the mind and the body as a whole. The initial traumatic event and the consequent neurological disruption trigger immune, endocrine, and multisystem dysfunction, which in turn affect the patient's psyche and well-being. In the present review, we will explore the most important local and systemic consequences of SCI from a PNIE perspective, defining the changes occurring in each system and how all these mechanisms are interconnected. Finally, potential clinical approaches derived from this knowledge will also be collectively presented with the aim to develop integrative therapies to maximize the clinical management of these patients.

Early surgery improves peripheral motor axonal dysfunction in acute traumatic central cord syndrome: A prospective cohort study

OBJECTIVE

To investigate the impact of early vs. delayed surgical decompression on peripheral motor axonal dysfunction following acute traumatic central cord syndrome (ATCCS).

METHODS

Both axonal excitability testing and motor unit number estimation (MUNE) were performed in 30 ATCCS patients (early- vs. delayed-surgical treatment: 12 vs. 18) before operation and 28 healthy subjects. Axonal excitability testing was repeated 3-5 days and 1-year after operation, and MUNE was re-evaluated 1-year after operation.

RESULTS

Preoperatively, an obvious modification in membrane potentials was observed in ATCCS patients that mostly coincided with depolarization-like features, and MUNE further revealed reduced motor units in tested muscles (P < 0.05). Unlike delayed-surgical cases, early-surgical cases showed recoveries of most measurements of axonal excitabilities soon after operation (P < 0.05). Postoperative one-year follow-up demonstrated that greater motor unit numbers in tested muscles were obtained in early-surgical cases than in delayed-surgical cases (P < 0.05).

CONCLUSIONS

ATCCS has adverse downstream effects on peripheral nervous system, even in the early stage of ATCCS. Early surgical treatment can ameliorate both excitability abnormalities and motor unit loss in distal motor axons.

SIGNIFICANCE

Optimizing axonal excitability in the early phases of ATCCS may alleviate peripheral nerve injury secondary to lesions of upper motor neuron and improve clinical outcomes.

Lower Motor Neuron Abnormality in Chronic Cervical Spinal Cord Injury: Implications for Nerve Transfer Surgery

Nerve transfer surgery (NT) constitutes an exciting option to improve upper limb functions in chronic spinal cord injury (SCI), but requires intact sublesional lower motor neuron (LMN) health. The purpose of this study was to characterize patterns of LMN abnormality in nerve-muscle groups that are the potential recipients of NT, using a standardized electrodiagnostic examination, in individuals with chronic SCI (injury duration >2 years, injury levels C4-T1). The LMN abnormality was determined using a semihierarchical approach, combining the amplitude compound muscle action potential (CMAP) and abnormal spontaneous activity on needle electromyography (EMG). Ten participants (46 potential recipient muscles) were included (median age, 42.5 years; six males and four females; median duration from injury, 15.5 years). A high frequency of LMN abnormality was observed (87%), although there was substantial variation within and between individuals. No statistically significant discordance was observed between LMN abnormality on CMAP and EMG (p = 0.24), however, 50% of muscles with normal CMAP demonstrated abnormal spontaneous activity. The high frequency of LMN abnormality in recipient nerve-muscle groups has implications to candidate selection for NT surgery in chronic SCI and supports the important role of the pre-operative electrodiagnostic examination. Our results further support the inclusion of both CMAP and needle EMG parameters for characterization of LMN health. Although the number of nerve-muscle groups with normal LMN health was small (13%), this underscores the neurophysiological potential of some patients with chronic injuries to benefit from NT surgery.

How to Identify Responders and Nonresponders to Dorsal Root Ganglion-Stimulation Aimed at Eliciting Motor Responses in Chronic Spinal Cord Injury: Post Hoc Clinical and Neurophysiological Tests in a Case Series of Five Patients

Objective

While integrity of spinal pathways below injury is generally thought to be an important factor in the success‐rate of neuromodulation strategies for spinal cord injury (SCI), it is still unclear how the integrity of these pathways conveying the effects of stimulation should be assessed. In one of our institutional case series of five patients receiving dorsal root ganglion (DRG)‐stimulation for elicitation of immediate motor response in motor complete SCI, only two out of five patients presented as responders, showing immediate muscle activation upon DRG‐stimulation. The current study focuses on post hoc clinical‐neurophysiological tests performed within this patient series to illustrate their use for prediction of spinal pathway integrity, and presumably, responder‐status.

Materials and Methods

In a series of three nonresponders and two responders (all male, American Spinal Injury Association [ASIA] impairment scale [AIS] A/B), a test‐battery consisting of questionnaires, clinical measurements, as well as a series of neurophysiological measurements was performed less than eight months after participation in the initial study.

Results

Nonresponders presented with a complete absence of spasticity and absence of leg reflexes. Additionally, nonresponders presented with close to no compound muscle action potentials (CMAPs) or Hofmann(H)‐reflexes. In contrast, both responders presented with clear spasticity, elicitable leg reflexes, CMAPs, H‐reflexes, and sensory nerve action potentials, although not always consistent for all tested muscles.

Conclusions

Post hoc neurophysiological measurements were limited in clearly separating responders from nonresponders. Clinically, complete absence of spasticity‐related complaints in the nonresponders was a distinguishing factor between responders and nonresponders in this case series, which mimics prior reports of epidural electrical stimulation, potentially illustrating similarities in mechanisms of action between the two techniques. However, the problem remains that explicit use and report of preinclusion clinical‐neurophysiological measurements is missing in SCI literature. Identifying proper ways to assess these criteria might therefore be unnecessarily difficult, especially for nonestablished neuromodulation techniques.

Morphology of Donor and Recipient Nerves Utilised in Nerve Transfers to Restore Upper Limb Function in Cervical Spinal Cord Injury

Loss of hand function after cervical spinal cord injury (SCI) impacts heavily on independence. Multiple nerve transfer surgery has been applied successfully after cervical SCI to restore critical arm and hand functions, and the outcome depends on nerve integrity. Nerve integrity is assessed indirectly using muscle strength testing and intramuscular electromyography, but these measures cannot show the manifestation that SCI has on the peripheral nerves. We directly assessed the morphology of nerves biopsied at the time of surgery, from three patients within 18 months post injury. Our objective was to document their morphologic features. Donor nerves included teres minor, posterior axillary, brachialis, extensor carpi radialis brevis and supinator. Recipient nerves included triceps, posterior interosseus (PIN) and anterior interosseus nerves (AIN). They were fixed in glutaraldehyde, processed and embedded in Araldite Epon for light microscopy. Eighty percent of nerves showed abnormalities. Most common were myelin thickening and folding, demyelination, inflammation and a reduction of large myelinated axon density. Others were a thickened perineurium, oedematous endoneurium and Renaut bodies. Significantly, very thinly myelinated axons and groups of unmyelinated axons were observed indicating regenerative efforts. Abnormalities exist in both donor and recipient nerves and they differ in appearance and aetiology. The abnormalities observed may be preventable or reversible.

Pelvic floor electrophysiology in spinal cord injury

OBJECTIVE

The study aimed to investigate sacral peripheral nerve function and continuity of pudendal nerve in patients with chronic spinal cord injury (SCI) using pelvic floor electrophysiological tests.

METHODS

Twelve patients with low cervical or thoracic SCI were prospectively included. Quantitative external anal sphincter (EAS) muscle electromyography (EMG), pudendal nerve terminal motor latency (PNTML) testing, bulbocavernosus reflex (BCR) testing and pudendal short-latency somatosensory-evoked potential (SEP) measurement were performed.

RESULTS

In EAS muscle EMG, two patients had abnormal increased spontaneous activity and seven prolonged motor unit potential duration. PNTML was normal in 10 patients. BCR was present with normal latency in 11 patients and with prolonged latency in one. The second component of BCR could be recorded in four patients. SEPs showed absent cortical responses in 11 patients and normal latency in one.

CONCLUSIONS

Pudendal nerve and sacral lower motor neuron involvement are significantly associated with chronic SCI, most prominently in EAS muscle EMG. The frequent finding of normal PNTML latencies supports earlier concerns on the utility of this test; however, BCR and pudendal SEPs may have clinical relevance.

SIGNIFICANCE

As intact peripheral nerves including pudendal nerve are essential for efficient supportive therapies, pelvic floor electrophysiological testing prior to these interventions is highly recommended.