Electrophysiological mapping of the segmental innervation of the saphenous and sural nerves

Utility of Sensory Nerve Conduction Study in Radiologically Positive Lumbosacral Plexopathy

MRI is the most appropriate imaging method for visual evaluation of lumbosacral plexopathy (LSP) and a reference for comparing with nerve conduction study (NCS). Eight patients with clinical, electrophysiological, and lumbosacral plexus MRI findings suggestive of LSP were prospectively recruited. Saphenous nerve abnormalities were present in seven patients (88%), compared to three for the superficial fibular (38%), and three for the sural nerve (38%). MRI showed tumor, hematoma, abscess, contrast enhancement, or hyperintense signals on the T2-weighted sequences. The SN has the highest yield in MRI positive LSP and may be a vital adjunct for electrophysiological evaluation of LSP.

Selective Dorsal Rhizotomy for the Treatment of Spastic Triplegic Cerebral Palsy

Background

Spastic triplegia is a recognized subtype of cerebral palsy (CP). In the course of treating spastic triplegic children with selective dorsal rhizotomy (SDR), we found that some children who had “minimal or mild involvement” in the stronger arm improved strikingly after undergoing SDR. Some of them became independent ambulators, which was an outcome that is not usually achieved in spastic quadriplegic children. However, the literature currently contains no data on the natural clinical course and the effects of CP interventions on spastic triplegia.

Objectives

Our aim was to elucidate the clinical characteristics of spastic triplegia and the effects of SDR on functional outcomes and the quality of life after childhood SDR.

Methods

The Institutional Review Board of the Washington University School of Medicine approved this quality of life survey (number: 201908177). The subjects of this study were children and adults (ages: 3.9-23.8 years at the time of the survey completion; mean: 12.1 ± 5.1 years) with spastic triplegic CP who had undergone SDR (ages: 2.2-15.9 years; mean: 6.1 ± 3.2 years) between 2003 and 2018 at the St. Louis Children’s Hospital. The follow-up period ranged from 1-16 years (mean: 6.0 ± 4.3 years). The study included a 76-patient cohort selected from a total of 253 spastic triplegic CP patients who had undergone SDR. All 253 patients were contacted via email or postal mail soliciting their participation in the study including the survey. The cohort included all patients who responded. The survey included questions on demographic information, quality of life, perceptions of health and the SDR procedure, motor and ambulatory functions, braces and orthotics, pain issues, side effects of SDR, and post-SDR treatment.

Results

Thirteen patients had presented with scissored gait, and these patients had undergone partial ventral rhizotomy (PVR) of L1-3 ventral roots immediately after the completion of SDR. Of note, 91% of 76 patients reported that SDR improved their quality of life, and 93% would recommend the procedure to other patients. After SDR, 21 more patients were able to run, 14 more played recreational sports, and 18 more could walk without using walking aids. Sixteen fewer patients used a wheelchair for long-distance walking and in crowds; 37 and 32 patients reported an improvement in the more affected arm and hand, respectively. Sixty-eight patients were able to regularly strengthened their muscles at least once a week, and 60 patients regularly stretched their legs. However, 53 patients required assistance with bathing or showering, 50 with getting dressed, and 56 with grooming or hygiene. Forty-eight patients had orthopedic surgery after SDR. Percutaneous hamstring-lengthening was the most common type of orthopedic surgery performed. Three of 13 patients who received PVR and SDR required adductor release. Six patients used medications for spasticity or dystonia. No late side effects of SDR were observed.

Conclusions

Our report elucidates the clinical features of spastic triplegia before and after SDR. A distinct clinical feature was the wide variation in ambulatory functions, ranging from total independent walking to wheelchair mobility. The vast majority of patients felt that SDR improved their motor functions and quality of life. PVR also resulted in favorable outcomes, with only three of 13 patients requiring additional adductor release surgery. There were no late complications related to SDR surgery.

The control of alternative splicing by SRSF1 in myelinated afferents contributes to the development of neuropathic pain

Neuropathic pain results from neuroplasticity in nociceptive neuronal networks. Here we demonstrate that control of alternative pre-mRNA splicing, through the splice factor serine-arginine splice factor 1 (SRSF1), is integral to the processing of nociceptive information in the spinal cord. Neuropathic pain develops following a partial saphenous nerve ligation injury, at which time SRSF1 is activated in damaged myelinated primary afferent neurons, with minimal found in small diameter (IB₄ positive) dorsal root ganglia neurons. Serine arginine protein kinase 1 (SRPK1) is the principal route of SRSF1 activation. Spinal SRPK1 inhibition attenuated SRSF1 activity, abolished neuropathic pain behaviors and suppressed central sensitization. SRSF1 was principally expressed in large diameter myelinated (NF200-rich) dorsal root ganglia sensory neurons and their excitatory central terminals (vGLUT1+ve) within the dorsal horn of the lumbar spinal cord. Expression of pro-nociceptive VEGF-A_xxxa within the spinal cord was increased after nerve injury, and this was prevented by SRPK1 inhibition. Additionally, expression of anti-nociceptive VEGF-A_xxxb isoforms was elevated, and this was associated with reduced neuropathic pain behaviors. Inhibition of VEGF receptor-2 signaling in the spinal cord attenuated behavioral nociceptive responses to mechanical, heat and formalin stimuli, indicating that spinal VEGF receptor-2 activation has potent pro-nociceptive actions. Furthermore, intrathecal VEGF-A₁₆₅a resulted in mechanical and heat hyperalgesia, whereas the sister inhibitory isoform VEGF-A₁₆₅b resulted in anti-nociception. These results support a role for myelinated fiber pathways, and alternative pre-mRNA splicing of factors such as VEGF-A in the spinal processing of neuropathic pain. They also indicate that targeting pre-mRNA splicing at the spinal level could lead to a novel target for analgesic development.

The effects from lumbar nerve root transection in rats on spinal somatosensory and motor-evoked potentials

STUDY DESIGN

Spinal somatosensory-evoked potentials (SSEPs), elicited by mixed nerve and dermatomal stimulation, and compound evoked muscle potentials (CMAPs), elicited by lower thoracic interspinous space stimulation, were recorded in rats that underwent single nerve root transection.

OBJECTIVES

To investigate and compare the effects of single nerve root transection using various electrophysiological models and to define a monitoring strategy that can easily and accurately predict compromise caused by a single lumbosacral nerve root injury.

SUMMARY OF BACKGROUND DATA

Neuromonitoring is an important and effective preventive measure against neurologic complications during spinal surgery, but monitoring the lumbosacral nerve roots is not well established.

METHODS

Rats received (Group I) a sham operation or had the (Group II) left L4, (Group III) L5, or (Group IV) L6 nerve root transected. SSEP were recorded at the thoracolumbar junction following stimulation of the sciatic nerve (M-SSEP) and the L5 dermatome (D-SSEP). CMAP was recorded at the intrinsic muscles of the foot by electrical stimulation in the lower thoracic spinal cord. Potentials recorded before and after a single nerve root transection were compared and correlated with clinical status by walking-track analysis 1 week later.

RESULTS

Relative amplitudes in Group II were 54.1% (M-SSEP), 84.6% (D-SSEP), and 85.5% (CMAP); 25.2% (M-SSEP), 66.5% (D-SSEP), and 85.8% (CMAP) in Group III; and 66.5% (M-SSEP), 95.5% (D-SSEP), and 23.2% (CMAP) in Group IV. M-SSEP is sensitive but not specific to single nerve root injury. D-SSEP and CMAP are less sensitive but more specific.

CONCLUSIONS

Injury to a single lumbosacral nerve root is diagnosed more easily with M-SSEP. With D-SSEP and CMAP, it was possible to differentiate the lesioned nerve root by stimulating the primary dermatome or recording from the innervated muscle. M-SSEP is an easy-sampling and appropriate tool for screening nerve root injury; its poor specificity may be overcome by using D-SSEP and CMAP in addition. Optimal monitoring of the lumbosacral nerve roots during lumbar spinal surgery requires the administration of M-SSEP, D-SSEP, and CMAP to provide independent verification of lumbosacral nerve root integrity and to allow detection of the occasional injuries that selectively affect either the sensory or motor system.

Electrophysiological evidence for afferent nerve fibers in human ventral roots

This study was designed to test the hypothesis that ventral roots in humans contain afferent nerve fibers. We made direct electrophysiological recordings of compound nerve action potentials in dorsal and ventral roots in children undergoing selective dorsal rhizotomy for spastic cerebral palsy. We stimulated the saphenous or sural nerves, which are pure sensory nerves, with electrical stimuli while systematically recording from ventral and dorsal roots from L3 to S2. In addition to the dorsal root nerve action potentials which we expected, we found smaller compound nerve action potentials, which were clearly afferent, in the ventral roots. This confirms the limited amount of experimental evidence that ventral roots do contain some afferent nerve fibers. The functional significance of these observations is not yet clear.

Selective lumbosacral dorsal rhizotomy immediately caudal to the conus medullaris for cerebral palsy spasticity

We describe a variation of selective dorsal rhizotomy for spastic cerebral palsy that involves sectioning of the dorsal spinal roots immediately caudal to the conus medullaris. The operation entails an L1-L2 laminectomy, ultrasonographic localization of the conus medullaris, and partial deafferentation of the L1-S2 roots with electromyographic testing under an operating microscope. In 66 children with cerebral palsy, the operation reduced spasticity in the lower extremity without complications, e.g., motor weakness, neurogenic bladder, and sensory loss. It offers several important advantages over alternative techniques.