Trans-synaptic degeneration of motoneurons distal to chronic cervical spinal cord compression in cervical spondylotic myelopathy

Neuromuscular consequences of spinal cord injury: New mechanistic insights and clinical considerations

The spinal cord facilitates communication between the brain and the body, containing intrinsic systems that work with lower motor neurons (LMNs) to manage movement. Spinal cord injuries (SCIs) can lead to partial paralysis and dysfunctions in muscles below the injury. While traditionally this paralysis has been attributed to disruptions in the corticospinal tract, a growing body of work demonstrates LMN damage is a factor. Motor units, comprising the LMN and the muscle fibers with which they connect, are essential for voluntary movement. Our understanding of their changes post-SCI is still emerging, but the health of motor units is vital, especially when considering innovative SCI treatments like nerve transfer surgery. This review seeks to collate current literature on how SCI impact motor units and explore neuromuscular clinical implications and treatment avenues. SCI reduced motor unit number estimates, and surviving motor units had impaired signal transmission at the neuromuscular junction, force-generating capacity, and excitability, which have the potential to recover chronically, yet the underlaying mechanisms are unclear. Furthermore, electrodiagnostic evaluations can aid in assessing the health lower and upper motor neurons, identify suitable targets for nerve transfer surgeries, and detect patients with time sensitive injuries. Lastly, many electrodiagnostic abnormalities occur in both chronic and acute SCI, yet factors contributing to these abnormalities are unknown. Future studies are required to determine how motor units adapt following SCI and the clinical implications of these adaptations.

Loss of cervical sagittal alignment worsens the cervical spinal lesions in patients with Hirayama disease

OBJECTIVE

To quantify the cervical sagittal alignment in patients with Hirayama disease (HD) and to investigate the effect of loss of cervical sagittal alignment upon the cervical spinal lesions in HD.

METHODS

Cervical sagittal alignments were measured in 253 HD patients and 63 healthy subjects by C2-C7 Cobb and a modified method of Toyama et al. Motor unit number estimation (MUNE) was performed in bilateral abductor pollicis brevis (APB) in all HD patients, and 31 patients further underwent cervical diffusion tensor imaging (DTI).

RESULTS

Compared with healthy subjects, HD patients showed lower C2-C7 Cobb (P < 0.05), and 83.4% patients showed loss of cervical lordosis (cervical straight or kyphosis), which was greater than healthy subjects (55.6%, P < 0.05). Compared with lordotic/straight group, patients with cervical kyphosis showed lower MUNE values and greater single motor unit potential (SMUP) in bilateral APB, and higher apparent dispersion coefficient (ADC) and lower fractional anisotropy were observed at C4/C5 level in the latter than the former (P < 0.05). C2-C7 Cobb was associated with both C4/C5 ADC and bilateral SMUP (P < 0.05).

CONCLUSIONS

Most HD patients showed loss of cervical sagittal alignments, and both MUNE and DTI detections demonstrated a positive correlation between loss of cervical sagittal alignments and cervical spinal lesions in HD. These findings supported that loss of cervical sagittal alignments may worsen motor impairments in HD. Therefore, it is necessary for clinicians to be aware of restoring cervical sagittal alignments during HD treatment.

Degeneration of the Sensorimotor Tract in Degenerative Cervical Myelopathy and Compensatory Structural Changes in the Brain

Degenerative cervical myelopathy is a progressive neurodegenerative disease, that has become increasingly prevalent in the aging population worldwide. The current study determined the factors affecting degeneration in the sensorimotor tract with degenerative cervical myelopathy and its relationship with brain structure. We divided patients into hyperintensity (HS) and non-hyperintensity (nHS) groups and measured the fractional anisotropy and apparent diffusion coefficients of the lateral corticospinal tract (CST), fasciculus gracilis and fasciculus cuneatus (FGC). Voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) techniques were used to estimate brain structure changes. Correlation of the modified Japanese Orthopaedic Association (mJOA) score, light touch, pinprick, motor score, and fractional anisotropy (FA) ratios of the CST at different levels were analyzed. Compared to healthy controls, the FA ratios of CST in the HS and nHS groups were decreased at all levels, and the apparent diffusion coefficient (ADC) ratio was increased only at C4/5 levels in the HS group. The FA ratio of FGC was decreased at the C3/4 and C4/5 levels in the HS group and only decreased at the C4/5 level in the nHS group. The ADC ratio was decreased only at the C4/5 level in the HS group. VBM analysis revealed that the volume of the precentral gyrus, postcentral gyrus, and paracentral lobule increased in patients compared to controls. TBSS analysis found no statistical significance between the sensory and motor tracts in white matter. The volume of clusters in HS and nHS groups negatively correlated with the C1/2 FA ratio of the CST. The results showed that the degeneration distance of the CST was longer than the FGC, and the degeneration distance was related to the degree of compression and spinal cord damage. Structural compensation and the neurotrophin family may lead to enlargement of the brain.

Intraspinal Administration of Netrin-1 Promotes Locomotor Recovery after Complete Spinal Cord Transection

Complete spinal cord lesions interrupt the connection of all axonal projections with their neuronal targets below and above the lesion site. In particular, the interruption of connections with the neurons at lumbar segments after thoracic injuries impairs voluntary body control below the injury. The failure of spontaneous regrowth of transected axons across the lesion prevents the reconnection and reinnervation of the neuronal targets. At present, the only treatment in humans that has proven to promote some degree of locomotor recovery is physical therapy. The success of these strategies, however, depends greatly on the type of lesion and the level of preservation of neural tissue in the spinal cord after injury. That is the reason it is key to design strategies to promote axonal regrowth and neuronal reconnection. Here, we test the use of a developmental axon guidance molecule as a biological agent to promote axonal regrowth, axonal reconnection, and recovery of locomotor activity after spinal cord injury (SCI). This molecule, netrin-1, guides the growth of the corticospinal tract (CST) during the development of the central nervous system. To assess the potential of this molecule, we used a model of complete spinal cord transection in rats, at thoracic level 10-11. We show that in situ delivery of netrin-1 at the epicenter of the lesion: (1) promotes regrowth of CST through the lesion and prevents CST dieback, (2) promotes synaptic reconnection of regenerated motor and sensory axons, and (3) preserves the polymerization of the neurofilaments in the sciatic nerve axons. These anatomical findings correlate with a significant recovery of locomotor function. Our work identifies netrin-1 as a biological agent with the capacity to promote the functional repair and recovery of locomotor function after SCI. These findings support the use of netrin-1 as a therapeutic intervention to be tested in humans.

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.

An Unusual Pattern of Premature Cervical Spine Degeneration in STAT3-LOF

Loss of function mutations in STAT3 (STAT3-LOF; autosomal dominant hyper-IgE (Job's) syndrome) are associated with a variety of musculoskeletal manifestations, including scoliosis, osteoporosis, and minimal trauma fractures. This retrospective magnetic resonance (MR) imaging study sought to characterize an unusual pattern of cervical spine degeneration among a cohort of STAT3-LOF patients. Cervical spine MR images of the STAT3-LOF cohort (n = 38) were assessed for a variety of degenerative changes and compared to age-matched groups of controls (n = 42) without known immune or musculoskeletal abnormalities. A unique pattern of premature cervical spine degeneration was identified among the STAT3-LOF cohort which included straightening and eventual reversal of the normal cervical lordosis, mainly due to multi-level spondylolisthesis, as well as early development of spinal canal narrowing, cord compression, and myelomalacia. Cervical spine degeneration in the STAT3-LOF cohort was significantly worse than controls in both the 30-45 and 45 + age groups. Moderate to severe degenerative changes were present after age 30, and markedly worsened over time in several cases. Bone mineral density (BMD) had a moderate negative correlation with cervical degeneration severity and a strong negative correlation with age among STAT3-LOF participants. Cervical degeneration in STAT3-LOF appears to be progressive and could result in cord compromise if left unaddressed. Focused history and physical examination for signs of neurologic compromise as well as periodic MR imaging are thus recommended for the evaluation of premature cervical spine degeneration in STAT3-LOF patients after age 30 so that timely surgical interventions may be considered to prevent spinal cord damage and permanent neurological deficits.

Ultrasonic osteotome versus high-speed burr in cervical anterior vertebral subtotal resection: A retrospective study of 81 cases

AIM

This study aimed to investigate the safety and effectiveness of ultrasonic osteotome in cervical anterior vertebral subtotal resection.

METHODS

Retrospective clinical data were collated for 81 patients with cervical spondylotic myelopathy who required cervical anterior vertebral subtotal resection.

RESULTS

Group A (n=40) was treated with an ultrasonic osteotome and group B (n=41) with a high-speed burr. Vertebrectomy time, intraoperative blood loss, surgical complications, Japanese Orthopedic Association (JOA) scores and JOA score improvement were compared. Group A showed significantly shorter vertebrectomy time and significantly less intraoperative blood loss (P<0.05). In group A, dysphagia occurred in one patient, and superior laryngeal nerve injury in one. Urinary tract infection occurred in one patient in group B. JOA score in both groups significantly increased 3 days after surgery (P<0.05), and at last follow-up compared with 3 days after surgery (P<0.05).

CONCLUSION

Ultrasonic osteotome was a safe and effective tool for subtotal anterior cervical vertebral resection.

Motor unit number index detects the effectiveness of surgical treatment in improving distal motor neuron loss in patients with incomplete cervical spinal cord injury

BACKGROUND

Recovery of motor dysfunction is important for patients with incomplete cervical spinal cord injury (SCI). To enhance the recovery of muscle strength, both research and treatments mainly focus on injury of upper motor neurons at the direct injury site. However, accumulating evidences have suggested that SCI has a downstream effect on the peripheral nervous system, which may contribute to the poor improvement of the muscle strength after operation. The aim of this study is to investigate the impact of early vs. delayed surgical intervention on the lower motor neurons (LMNs) distal to the injury site in patients with incomplete cervical SCI.

METHODS

Motor unit number index (MUNIX) was performed on the tibialis anterior (TA), extensor digitorum brevis (EDB) and abductor hallucis (AH) in 47 patients with incomplete cervical SCI (early vs. delayed surgical-treatment: 17 vs. 30) and 34 healthy subjects approximately 12 months after operation. All patients were further assessed by American spinal injury association (ASIA) motor scales and Medical Research Council (MRC) scales.

RESULTS

There are no difference of both ASIA motor scores and MRC scales between the patients who accepted early and delayed surgical treatment (P > 0.05). In contrast, the patients undergoing early surgical treatment showed lower MUSIX values in both bilateral EDB and bilateral TA, along with greater MUNIX values in both right-side EDB and right-side TA, compared to the patients who accepted delayed surgical treatment (P < 0.05).

CONCLUSIONS

Cervical SCI has a negative effect on the LMNs distal to the injury site. Early surgical intervention in Cervical SCI patients may improve the dysfunction of LMNs distal to the injury site, reducing secondary motor neuron loss, and eventually improving clinical prognosis.

Early Surgical Decompression Ameliorates Dysfunction of Spinal Motor Neuron in Patients With Acute Traumatic Central Cord Syndrome: An Ambispective Cohort Analysis

STUDY DESIGN

An ambispective cohort analysis.

OBJECTIVE

The aim of this study was to investigate the impact of early (≤2 weeks) versus delayed (>2 weeks) surgical intervention on the spinal motor neurons at and distal to injury site in acute traumatic central cord syndrome (ATCCS).

SUMMARY OF BACKGROUND DATA

Accumulating evidence demonstrated degeneration in distal lower motor neurons (LMNs) following spinal cord injury, and this secondary degeneration may exacerbate motor impairments and limit spontaneous motor recovery. However, few studies involved this pathological process in ATCCS.

METHODS

Motor unit number estimation (MUNE) was performed on both abductor pollicis brevis (APB) and extensor digitorum brevis (EDB) in 69 ATCCS patients (early vs. delayed surgical-treatment: 29 vs. 35) and 42 healthy subjects. All patients were assessed by American spinal injury association and Medical Research Council scales. These examinations and disabilities of arm, shoulder, and hand (c) questionnaire were administered approximately 21 months after operation in 65 of these patients.

RESULTS

Preoperatively, MUNE values were lower in cervical-innervated muscles of ATCCS patients than in those of controls, and reduced motor units were observed in lumbosacral-innervated muscles in ATCCS patients with preoperative duration over 6 months (P < 0.05). Increased motor unit size without modification of MUNE values was found in delayed-surgical patients, whereas early-surgical patients mainly showed increased MUNE values in tested muscles between two assessments (P < 0.05). The postoperative follow-up analysis identified larger motor unit size and relatively fewer motor units in tested muscles, as well as higher DASH scores, in delayed-surgical patients than in early-surgical patients (P < 0.05).

CONCLUSION

ATCCS has adverse downstream effects on the LMNs distal to injury site. Surgical intervention within 2 weeks after injury in ATCCS patients may be beneficial in ameliorating dysfunction of spinal motor neurons at and distal to injury site, reducing secondary motor neuron loss, and eventually improving neurologic outcomes.

LEVEL OF EVIDENCE

3.

Exploring the receptor origin of vibration-induced reflexes

STUDY DESIGN

An experimental design.

OBJECTIVES

The aim of this study was to determine the latencies of vibration-induced reflexes in individuals with and without spinal cord injury (SCI), and to compare these latencies to identify differences in reflex circuitries.

SETTING

A tertiary rehabilitation center in Istanbul.

METHODS

Seventeen individuals with chronic SCI (SCI group) and 23 participants without SCI (Control group) were included in this study. Latency of tonic vibration reflex (TVR) and whole-body vibration-induced muscular reflex (WBV-IMR) of the left soleus muscle was tested for estimating the reflex origins. The local tendon vibration was applied at six different vibration frequencies (50, 85, 140, 185, 235, and 265 Hz), each lasting for 15 s with 3-s rest intervals. The WBV was applied at six different vibration frequencies (35, 37, 39, 41, 43, and 45 Hz), each lasting for 15 s with 3-s rest intervals.

RESULTS

Mean (SD) TVR latency was 39.7 (5.3) ms in the SCI group and 35.9 (2.7) ms in the Control group with a mean (95% CI) difference of -3.8 (-6.7 to -0.9) ms. Mean (SD) WBV-IMR latency was 45.8 (7.4) ms in the SCI group and 43.3 (3.0) ms in the Control group with a mean (95% CI) difference of -2.5 (-6.5 to 1.4) ms. There were significant differences between TVR latency and WBV-IMR latency in both the groups (mean (95% CI) difference; -6.2 (-9.3 to -3.0) ms, p = 0.0001 for the SCI group and -7.4 (-9.3 to -5.6) ms, p = 0.011 for Control group).

CONCLUSIONS

The results suggest that the receptor of origin of TVR and WBV-IMR may be different.

Changes in Central Motor Conduction Time and Its Implication on Dysfunction of Distal Upper Limb in Distal-Type Cervical Spondylotic Amyotrophy

PURPOSE

Distal-type cervical spondylotic amyotrophy (CSA) is an uncommon syndrome associated with cervical spondylosis. The pathogenic mechanism of distal-type CSA is still unclear. The aim of the current study was to analyze central motor conduction time (CMCT) in the cases with distal-type CSA and to investigate the role of cervical cord compressive injury in the distal-type CSA.

METHODS

Both 28 cases with distal-type CSA and 21 healthy subjects accepted CMCT measures, motor unit number estimation, handgrip strength examination, and magnetic resonance imaging evaluation.

RESULTS

In this study, nine (9/28, 32.1%) cases with CSA presented with prolonged CMCT, and both reduced number of motor units and decreased handgrip strength were found in these 9 cases (P < 0.05). Magnetic resonance imaging evaluation showed that 7 of these 9 patients presented with proximal cervical cord compression with or even without distal selective compression consistent with segmental atrophy. A negative relationship between CMCT and both number of motor units and handgrip strength was found on the symptomatic side (P < 0.05), and there was a positive correlation between CMCT and amplitude of single motor unit potentials on the less symptomatic side (P < 0.05).

CONCLUSIONS

Corticospinal tract damage caused by proximal spinal cord compression may induce distal motor unit loss to worsen in some cases with distal-type CSA, which may contribute to the dysfunction of the distal upper limb in some cases with distal-type CSA. Therefore, treatment and rehabilitation efforts should account for both distal selective compression and proximal cord compression in distal-type CSA.

Changes in the soleus H-reflex test and correlations between its results and dynamic magnetic resonance imaging abnormalities in patients with Hirayama disease

OBJECTIVE

To investigate changes in soleus H-reflex tests in patients with Hirayama disease (HD) and to analyse correlations between these changes and forward-shifting of the cervical cord during neck flexion.

METHODS

The amplitude of the soleus H-reflex with and without vibration on the Achilles tendon was recorded bilaterally in 81 HD patients and 34 controls to measure both the vibratory inhibition index (VII) and the H_max/M_max ratio. The maximum forward-shifting degree of cervical cord during neck flexion was measured using dynamic magnetic resonance imaging in all HD patients.

RESULTS

Significantly higher VII was recorded in 6/81 (7.4%) HD patients, along with abnormal H_max/M_max ratios in 5 of 6 cases. Compared to illness duration (r = 0.29-0.36, p < 0.05), the maximum forward-shifting degree of the cervical cord was more strongly correlated with both VII and the H_max/M_max ratio (r = 0.51-0.81, p < 0.05).

CONCLUSIONS

HD patients may develop cervical spinal cord injury with disease progression, and these lesions may be more likely to occur in cases with relatively severe cervical-flexion structural abnormalities even during early stages.

SIGNIFICANCE

More caution should be taken when managing HD patients with severe cervical-flexion abnormalities because of the possible early occurrence of upper motor neuron lesions.