Therapeutic efficacy of microtube-embedded chondroitinase ABC in a canine clinical model of spinal cord injury

Many hundreds of thousands of people around the world are living with the long-term consequences of spinal cord injury and they need effective new therapies. Laboratory research in experimental animals has identified a large number of potentially translatable interventions but transition to the clinic is not straightforward. Further evidence of efficacy in more clinically-relevant lesions is required to gain sufficient confidence to commence human clinical trials. Of the many therapeutic candidates currently available, intraspinally applied chondroitinase ABC has particularly well documented efficacy in experimental animals. In this study we measured the effects of this intervention in a double-blinded randomized controlled trial in a cohort of dogs with naturally-occurring severe chronic spinal cord injuries that model the condition in humans. First, we collected baseline data on a series of outcomes: forelimb-hindlimb coordination (the prespecified primary outcome measure), skin sensitivity along the back, somatosensory evoked and transcranial magnetic motor evoked potentials and cystometry in 60 dogs with thoracolumbar lesions. Dogs were then randomized 1:1 to receive intraspinal injections of heat-stabilized, lipid microtube-embedded chondroitinase ABC or sham injections consisting of needle puncture of the skin. Outcome data were measured at 1, 3 and 6 months after intervention; skin sensitivity was also measured 24 h after injection (or sham). Forelimb-hindlimb coordination was affected by neither time nor chondroitinase treatment alone but there was a significant interaction between these variables such that coordination between forelimb and hindlimb stepping improved during the 6-month follow-up period in the chondroitinase-treated animals by a mean of 23%, but did not change in controls. Three dogs (10%) in the chondroitinase group also recovered the ability to ambulate without assistance. Sensitivity of the dorsal skin increased at 24 h after intervention in both groups but subsequently decreased to normal levels. Cystometry identified a non-significant improvement of bladder compliance at 1 month in the chondroitinase-injected dogs but this did not persist. There were no overall differences between groups in detection of sensory evoked potentials. Our results strongly support a beneficial effect of intraspinal injection of chondroitinase ABC on spinal cord function in this highly clinically-relevant model of chronic severe spinal cord injury. There was no evidence of long-term adverse effects associated with this intervention. We therefore conclude that this study provides strong evidence in support of initiation of clinical trials of chondroitinase ABC in humans with chronic spinal cord injury

Spinal cord stimulation in chronic pain: evidence and theory for mechanisms of action.

Well-established in the field of bioelectronic medicine, Spinal Cord Stimulation (SCS) offers an implantable, non-pharmacologic treatment for patients with intractable chronic pain conditions. Chronic pain is a widely heterogenous syndrome with regard to both pathophysiology and the resultant phenotype. Despite advances in our understanding of SCS-mediated antinociception, there still exists limited evidence clarifying the pathways recruited when patterned electric pulses are applied to the epidural space. The rapid clinical implementation of novel SCS methods including burst, high frequency and dorsal root ganglion SCS has provided the clinician with multiple options to treat refractory chronic pain. While compelling evidence for safety and efficacy exists in support of these novel paradigms, our understanding of their mechanisms of action (MOA) dramatically lags behind clinical data. In this review, we reconstruct the available basic science and clinical literature that offers support for mechanisms of both paresthesia spinal cord stimulation (P-SCS) and paresthesia-free spinal cord stimulation (PF-SCS). While P-SCS has been heavily examined since its inception, PF-SCS paradigms have recently been clinically approved with the support of limited preclinical research. Thus, wide knowledge gaps exist between their clinical efficacy and MOA. To close this gap, many rich investigative avenues for both P-SCS and PF-SCS are underway, which will further open the door for paradigm optimization, adjunctive therapies and new indications for SCS. As our understanding of these mechanisms evolves, clinicians will be empowered with the possibility of improving patient care using SCS to selectively target specific pathophysiological processes in chronic pain

Electrophysiological markers for neuropathic pain in spinal cord injured subjects

Physical disability following spinal cord injury (SCI) is the most striking problem noted by the general public. But for the affected subjects urogenital difficulties or depression and pain are often more burdensome. Pain after SCI can have various reasons but only neuropathic pain below the level of lesion (bNP) is thought to be caused by injury of the spinal nervous tissue. This type of pain is in the focus of this thesis. Once bNP has established it is mostly chronic and medication is generally ineffective. Currently, more and more treatments trying to restore function after SCI enter the clinical trial phase. Besides improving function, however, treatments increasing nerve growth in the spinal cord risk to induce or exacerbate bNP. Therefore, observation of bNP is a crucial factor in such interventional studies. A method to objectively supervise bNP has, however, not yet been established. The spinothalamic tract (STT) mainly transmits nociceptive and temperature information in the spinal cord. This tract was dysfunctional in SCI subjects suffering from bNP in clinical examinations. Nevertheless, STT dysfunction was not predictive for bNP and sensory differences between subjects with and without bNP could not be detected. In contrast to clinical examination which is always subjective and only offers limited resolution, electrophysiological measures allow for a more detailed and objective investigation. The novel electrophysiological method of contact heat evoked potentials (CHEP) measures STT function. Establishment of this method was the goal of the first study. The painful stimulation on locations along the spine allowed the calculation of the conduction velocity of the STT in healthy subjects. Furthermore the CHEP latency depended linearly on the heat pain threshold with 1° C higher threshold leading to approximately 10 ms longer latency. It was hypothesized that the rather low heating rate combined with the time-consuming passive heat spread from skin surface to nociceptors was responsible for this. The second study aimed at clarifying this dependence through comparison of the results of study 1 with those of a theoretical heat transfer model. According to this model, 1° C higher pain threshold leads to approximately 15 ms longer CHEP latency. The close similarity between the experimentally determined (study 1) and the computed dependence, proved the influence of the pain threshold on CHEP latency. Summary Electrophysiological markers for Neuropathic Pain in SCI Subjects 2 Subjects suffering from neuropathic pain (NP) in general and not only in SCI, have lowered EEG peak frequency. It was hypothesized in literature that the reduced EEG peak frequency emerged from thalamic deafferentiation and from the ensuing dysrhythmia in thalamocortical feedback loops. Therefore, the third study investigated EEG peak frequency in addition to STT function and compared both between SCI subjects with and without bNP and controls. The STT function (measured with CHEP) below the level of injury was distinctly impaired in SCI compared to control subjects. Furthermore, the EEG peak frequency was generally lower in the SCI subjects. While the CHEP measurements did not reveal differences between subjects with and without bNP, the EEG peak frequency was lowered in subjects with bNP. This difference, however, was only apparent after the linear dependence of EEG peak frequency from the level of SCI was taken into account. In consideration of this dependence, the EEG peak frequency could in future be helpful to supervise bNP both in studies aiming at restoring function or reducing pain after SCI. Currently, the clinical read-out parameter for STT function is pinprick sensation. In the fourth study this pinprick sensation was traced over the first year after SCI. Comparison of this STT function with the bNP state of the same subjects 2-5 years after SCI disclosed larger functional STT recovery in subjects suffering from bNP. Despite the different STT functional recovery, the initial and end measurements did not discriminate between subjects with and without bNP. This was in agreement with earlier studies. The results corroborate the above mentioned hypothesis that new therapies intending to promote sensorimotor recovery after SCI could simultaneously induce bNP by boosting recovery of spinothalamic function

Electrophysiological mapping of rat sensorimotor lumbosacral spinal networks after complete paralysis

Stimulation of the spinal cord has been shown to have great potential for improving function after motor deficits caused by injury or pathological conditions. Using a wide range of animal models, many studies have shown that stimulation applied to the neural networks intrinsic to the spinal cord can result in a dramatic improvement of motor ability, even allowing an animal to step and stand after a complete spinal cord transection. Clinical use of this technology, however, has been slow to develop due to the invasive nature of the implantation procedures and the difficulty of ascertaining specific sites of stimulation that would provide optimal amelioration of the motor deficits. Moreover, the development of tools available to control precise stimulation chronically via biocompatible electrodes has been limited. In this chapter, we outline the use of a multisite electrode array in the spinal rat model to identify and stimulate specific sites of the spinal cord to produce discrete motor behaviors in spinal rats. The results demonstrate that spinal rats can stand and step when the spinal cord is stimulated tonically via electrodes located at specific sites on the spinal cord. The quality of stepping and standing was dependent on the location of the electrodes on the spinal cord, the specific stimulation parameters, and the orientation of the cathode and anode. The spinal motor evoked potentials in selected muscles during standing and stepping are shown to be critical tools to study selective activation of interneuronal circuits via responses of varying latencies. The present results provide further evidence that the assessment of functional networks in the background of behaviorally relevant functional states is likely to be a physiological tool of considerable importance in developing strategies to facilitate recovery of motor function after a number of neuromotor disorders

The role of peripheral input and its contribution to phantom limb pain

Following amputation, nearly all amputees report non-painful phantom phenomena and many of them suffer from chronic phantom limb pain (PLP) and residual limb pain (RLP). The etiology of PLP remains elusive and there is an ongoing debate on the role of peripheral and central mechanisms. Few studies have examined the entire somatosensory pathway from the truncated nerves to the cortex in amputees with PLP compared to those without PLP. The relationship between afferent input, somatosensory responses and the change in PLP remains unclear. The present thesis aimed at identifying whether peripheral afferent input can induce PLP and how it interacts with somatosensory processing and postamputation pain. Transcutaneous electrical nerve stimulation was applied on the truncated median nerve, the skin of the residual limb and the contralateral homologous nerve in twenty-two traumatic upper-limb amputees (12 with and 10 without PLP). Using somatosensory event-related potentials, the ascending volley was monitored through the brachial plexus, the spinal cord, the brainstem and the thalamus to the primary somatosensory cortex. There were no significant differences in the electrical potentials generated by the stimulation from the truncated nerve or the skin of the residual limb in amputees with and without PLP. Peripheral input could evoke PLP in amputees with chronic PLP (7/12), but not in amputees without a history of PLP (0/10). In addition, peripherally induced potentials through the spinal-subcortical segment were significantly positively associated with evoked RLP, but not PLP. Peripheral input can enhance PLP but seems insufficient to cause it. These findings indicate the multifactorial complexity of PLP and also suggest different mechanisms for PLP and RLP

Long-Term Paired Associative Stimulation for Restoration of Motor Function after Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition and consequent loss of motor control remains one of the main causes of disability. Motor recovery after SCI depends on the amount of spared and restored neural connections in the spinal cord. Most SCIs are incomplete and even neurologically complete injuries possess some spared neural connections. Damaged motor pathways can be reactivated by external stimulation. However, current treatment approaches are mainly palliative, such as assisting adaptation to impairments. Thus, there is a need for novel therapies to induce neuroplasticity in the spinal cord and strengthen weak and disrupted neural connections. In this thesis, paired associative stimulation (PAS) was applied as a long-term treatment for chronic incomplete SCI of traumatic origin. PAS is a non-invasive neuromodulation paradigm where descending volleys induced by transcranial magnetic stimulation (TMS) of the motor cortex are timed to coincide with antidromic volleys elicited by peripheral nerve electrical stimulation (PNS). The stimulation protocol was designed to coincide TMS- and PNS-induced volleys at the cortico-motoneuronal synapses in the spinal cord. Continuous pairing of TMS and PNS stimuli can change synaptic efficacy and produce long-term potentiation (LTP)-like plasticity in the corticospinal tract. Augmentation of synaptic strength at the spinal level has clear therapeutic value for SCI, as it can enhance motor control over paralyzed muscles. The aim of the thesis was to investigate the possible therapeutic effects of long-term PAS on hand and leg motor function in individuals with chronic incomplete SCI of traumatic origin. Study I explored long-term PAS therapeutic potential by providing long-term PAS until full recovery of hand muscle strength or until improvements ceased. The PAS protocol was designed to coincide TMS- and PNS-induced volleys in the cervical spinal cord, which is both the location of the stimulated lower motor neuron cell bodies and the site of the injury. Improvements up to normal values of hand muscle strength (Manual Muscle Test [MMT]) and increased amplitude of motor evoked potentials (MEPs) were obtained after more than 1-year stimulation in a participant with SCI. The participant regained almost complete self-care of the upper body. This was the first demonstration of restoring normal strength and range of movement of individual hand muscles by means of long-term PAS. The effect persisted over 6 months of follow up. Study II probed the effects of long-term PAS on leg muscle strength and walking in a group of five people with SCI. The PAS protocol was designed to coincide TMS- and PNS-induced volleys in the lumbar spinal cord but the site of the injury was in the cervical spinal cord. Long-term PAS delivered for 2 months significantly increased the total lower limb MMT score. This effect was stable over a 1-month follow up. Walking speed increased after 2 months of PAS in all participants. This study was the first demonstration that long-term PAS may significantly increase leg muscle strength and affect walking. The MMT score prior to the intervention was a good predictor of changes in walking speed. Study III developed a novel technique that enables probing neural excitability at the cervical spinal level by utilizing focal magnetic coil and anatomy-specific models for re-positioning of the coil. The technique enabled recording of highly reproducible MEPs and was suitable for accurate maintenance and retrieval of the focal coil position at the cervical level. In summary, this thesis contributes to the understanding of therapeutic efficacy of long-term PAS for restoration of motor control over hand and leg muscles after chronic SCI. This work challenges the view that chronic SCI is an irreversible pathologic condition and demonstrates the possibility of restoring neurological function many years postinjury when spontaneous recovery is extremely rare. The increased amplitude of MEPs, sustainable motor improvements, and the effects observed regardless of injury location indicate that PAS induces stable changes in the corticospinal pathways.Selkäydinvamma on ihmiseen kokonaisvaltaisesti vaikuttava tila, ja motorinen heikkous on yksi tärkeimmistä tekijöistä, jotka aiheuttavat rajoituksia päivittäiseen elämään. - Nykyiset hoitomenetelmät pääasiassa lievittävät oireita. Ne helpottavat kivun ja spastisuuden hallintaa ja sopeutumista vammaan sekä estävät sekundaarisia komplikaatioita. Keskushermosto voi kuitenkin järjestyä uudelleen sopeutuakseen heikentyneeseen toimintaan, ja tätä muovautuvuutta voidaan käyttää terapeuttisena mahdollisuutena. Vaurioituneet hermoradat voidaan aktivoida uudelleen ulkoisella stimulaatiolla. Toipuminen selkäydinvamman jälkeen riippuu niistä selkäytimen hermoyhteyksistä, jotka ovat säästyneet ja jotka on onnistuttu palauttamaan. Usein selkäydinvammat ovat osittaisia, ja neurologisesti täydellisissäkin vammoissa on joitakin säästyneitä hermoyhteyksiä. Uusilla hoitomenetelmillä voidaan aktivoida selkäytimen neuroplastisuutta ja vahvistaa heikkoja ja katkenneita hermoyhteyksiä. Tässä väitöskirjassa kaksoisstimulaatiota (PAS) käytettiin pitkäaikaisena hoitona potilailla, joilla oli krooninen, traumaattinen osittainen selkäydinvamma. PAS on neuromodulaatiomenetelmä, jossa aivokuoren transkraniaalinen magneettistimulaatio (TMS) synkronoidaan perifeeristen hermojen sähköstimulaatioon (PNS). Stimulaatioprotokolla suunniteltiin niin että TMS: n ja PNS: n synnyttämät aktivaatiot kohtaavat selkäytimen synapseissa. Jatkuva TMS:n ja PNS:n aikaansaamien ärsykkeiden kohtaaminen selkäydintasolla voi voimistaa synapsien tehokkuutta ja tuottaa pitkäaikaisen synaptisen potentiaation (long-term potentiation, LTP) selkäytimessä. Synaptisen tehokkuuden kasvu selkäytimessä todennäköisesti parantaa lihasten tahdonalaista hallintaa. Väitöskirjan päätavoitteena on ollut tutkia pitkäaikaisen kaksoisstimulaation (PAS) mahdollisia terapeuttisia vaikutuksia käden ja jalkojen tahdonalaiseen lihasaktiivisuuteen henkilöillä, joilla on traumaattinen krooninen osittainen selkäydinvamma. Tutkimuksessa I selvitin pitkäaikaista PASin terapeuttista potentiaalia antamalla PAS-hoitoa niin kauan kunnes käden lihasten voima palautui kokonaan, tai voimassa ei tapahtunut enää kasvua. Yli vuoden kestäneen stimulaation jälkeen käsien lihasvoimat kohenivat normaaliarvoihin (Manuaalinen lihastesti, MMT) osallistujalla, jolla oli krooninen osittainen neliraajahalvaus. Sen lisäksi herätevastet (motor-evoked potentials) kasvoivat. Koehenkilön ylävartalon lihashallinta palautui lähes täydellisesti. Tämä on ensimmäinen osoitus yksittäisten käsilihasten normaalin voiman ja liikeratojen palautumisesta pitkäaikaisen PAS:n avulla selkäydinvammapotilaalla. Vaikutus säilyi 6 kuukauden seurannassa. Tutkimuksessa II tutkittiin pitkäaikaisen PAS: n vaikutuksia alaraajalihasten voimaan ja kävelyyn viidellä henkilöllä, joilla on krooninen tetraplegia. Kahden kuukauden ajan annettu pitkäaikainen PAS lisäsi merkittävästi alaraajojen MMT-pistemäärää keskimäärin yhdellä pisteellä lihasta kohden. Tämä tulos säilyi kuukauden seurannassa. Kaikkien osallistujien kävelynopeus kasvoi PAS-hoitojakson jälkeen. Tutkimus on ensimmäinen osoitus siitä, että pitkäaikainen PAS voi lisätä merkittävästi alaraajojen lihasvoimaa. MMT-pistemäärä ennen interventiota ennusti hyvin kävelynopeuden muutoksia. Tutkimuksessa III kehitettiin uusi tekniikka, joka mahdollistaa magneettistimulaation selkäydinalueella käyttäen fokaalista magneettikelaa ja pään anatomisia malleja magneettikelan toistettuun kohdentamiseen. Menetelmä mahdollisti toistettavien MEP-signaalien mittaamisen sekä kelan sijainnin tarkan, toistettavan paikannuksen ja kohdentamisen niskan alueella. Yhteenvetona voidaan todeta, että väitöskirja lisää ymmärrystä pitkäaikaisen PAS: n terapeuttisesta tehosta ylä- ja alaraajalihasten hallinnan palauttamisessa ja omatoimisuuden lisäämisessä kroonisen selkäydinvamman jälkeen. Väitöskirja haastaa käsityksen kroonisen selkäydinvamman aiheuttamien toimintahäiriöiden pysyvästä luonteesta. Sen lisäksi väitöskirja osoittaa mahdollisuuden palauttaa lihasaktiivisuutta nimenomaan kroonisessa selkäydinvammassa, jossa spontaani koheneminen on erittäin harvinaista. Voimistuneet lihasvasteet ja pysyvä lihashallinnan parannus vamman sijainnista riippumatta osoittavat, että PAS oikein käytettynä muokkaa liikejärjestelmää hyödyllisellä tavalla