Emerging Therapies of Traumatic Spinal Cord Injury

Research Article | DOI: https://doi.org/doi.org/10.31579/jsdr.2

Emerging Therapies of Traumatic Spinal Cord Injury

*Corresponding Author:

Citation:

Copyright: © Tengo Lika 2018 et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Received: 30 November -0001 | Accepted: 02 May 2018 | Published: 09 May 2018

Keywords: Spinal cord injury; trauma; MRI; imaging; stem cell; neuroprotection; neuroregeneration

Abstract

Traumatic spinal cord injuries (SCIs) affect 1.3 million North Americans, producing devastating physical, social, and vocational impairment. Pathophysiologically, the initial mechanical trauma is followed by a significant secondary injury which includes local ischemia, pro-apoptotic signaling, release of cytotoxic factors, and inflammatory cell infiltration. Expedient delivery of medical and surgical care during this critical period can improve long-term functional outcomes, engendering the concept of “Time is Spine”. We emphasize the importance of expeditious care while outlining the initial clinical and radiographic assessment of patients. Key evidence-based early interventions (surgical decompression, blood pressure augmentation, and methylprednisolone) are also reviewed, including findings of the landmark Surgical Timing in Acute Spinal Cord Injury Study (STASCIS). We then describe other neuroprotective approaches on the edge of translation such as the sodium-channel blocker riluzole, the anti-inflammatory minocycline, and therapeutic hypothermia. We also review promising neuroregenerative therapies that are likely to influence management practices over the next decade including chondroitinase, Rho-ROCK pathway inhibition, and bioengineered strategies. The importance of emerging neural stem cell therapies to remyelinate denuded axons and regenerate neural circuits is also discussed. Finally, we outline future directions for research and patient care.

Introduction

Traumatic spinal cord injuries (SCIs) have devastating consequences for patients and families. Direct lifetime costs can be as high as $1.1–$4.6 million per patient, with over 1.3 million patients affected in North America alone 1, 2. Expedient delivery of specialized medical and surgical care can improve long-term functional outcomes for patients 3, 4. The rapidly evolving management of patients with SCI is summarized here with emphasis on evidence-based current practices and upcoming therapies in trial.

Pathophysiology

The initial primary trauma results in mechanical injury to cells, damages the sensitive microvasculature of the cord, and causes hemorrhage. Pro-apoptotic signaling is initiated and progressive edema contributes to ongoing ischemia 5, 6. Furthermore, the blood-spinal cord barrier is disrupted, permitting an influx of vasoactive peptides, cytokines, and inflammatory cells 7, 8. Over the ensuing hours to days, by-products of cellular necrosis are released (ATP, DNA, and K +), creating a cytotoxic post-injury milieu and activating microglia to further recruit phagocytes. Macrophages and polymorphonuclear leukocytes infiltrate and generate oxygen free radicals and other cytotoxic by-products.

As the parenchymal volume is lost, cystic cavities coalesce, creating a physical barrier to cell migration 11. Furthermore, the lack of structural framework impedes regenerative attempts. Over time, astrocytes proliferate and surround the perilesional zone, creating an irregular mesh-like barrier of interwoven cell processes 12. This is accompanied by fibroblast deposition of chondroitin sulfate proteoglycans (CSPGs) including neural/glial antigen 2 (NG2) and tenascin 1316. CSPGs and myelin glycoproteins act via the Rho-ROCK (rho-associated protein kinase) pathway to inhibit neurite outgrowth by signaling growth cone collapse through effector kinases 17. Together, these mechanisms severely restrict endogenous neural circuit regeneration and oligodendrocyte remyelination at a cellular level.

Systemically, cervical and thoracic cord injuries can interrupt the sympathetic output of the intermediolateral column, causing neurogenic shock with loss of peripheral vascular tone and bradycardia 18. The result can be profound hypotension, which further exacerbates cord ischemia 19. Paralysis of the intercostal and abdominal muscles restricts the inspiratory phase of ventilation, leading to hypercarbia and/or hypoxia. Furthermore, a weakened cough, poor mobilization, and secondary immunodeficiency (immune paralysis) after SCI make patients highly susceptible to life-threatening infections 20, 21.

Methods

Data sources

The NSCID began in 1973 and is believed to capture data from approximately 13% to 15% of new SCIs every year in the United States. Since its inception, 28 federally funded SCI Model System centers have contributed data to NSCID, including demographics, injury and medical characteristics, and functional independence during the initial hospitalization and at postinjury years 1 and 5 and every 5 years thereafter.20 Psychosocial outcomes and assistive technology information have also been obtained at each follow-up. The NSCID defines SCI as the occurrence of an acute traumatic lesion of neural elements in the spinal canal, resulting in temporary or permanent sensory and/or motor deficit. The clinical definition of SCI excludes intervertebral disc disease, vertebral injuries in the absence of SCI, nerve root avulsions and injuries to nerve roots and peripheral nerves outside the spinal canal, cancer, spinal cord vascular disease, and other nontraumatic spinal cord diseases. Details about this database have been described elsewhere.21

Study participantsThe present analyses are limited to persons enrolled in the NSCID and NSSCID who sustained a traumatic SCI between 2005 and 2011 (N=7,882). After excluding those with unknown etiology of injury (n=48), a total of 7,429 persons from 19 SCI Model System Centers and 405 persons from the 3 Shriners SCI units were included in this study. The participating SCI Model System centers and corresponding sample size are as follows: Alabama (n=432), California (n=76, from 2 centers), Colorado (n=946), District of Columbia (n=197), Florida (n=41), Georgia (n=1,907), Illinois (n=350), Massachusetts (n=232), Michigan (n=243), Missouri (n=34), New York (n=286), New Jersey (n=485), Ohio (n=265), Pennsylvania (n=968, from 2 centers), Texas (n=482), Virginia (n=29), and Washington (n=456).

Demographic and injury profile of study participants (N=7

Age group, years

  

  0-15

(21.5)

  61 and above

Sex

  

  Male

Race

  

  White, Non-Hispanic

(66.8)

  Black, Non-Hispanic

Level of injury

  

  C1-C4

Completeness of injury (AIS)

  

  A

Day of injury

  

  Monday

(11.7)

  Wednesday

Month of injury

  

  January

(9.1)

  September

 

Table 1 shows the participants’ characteristics.

Note: AIS = American Spinal Injury Association Impairment Scale.

Discussion

Demographic and injury profiles of the 7,834 persons with SCI enrolled in the NSCID and NSSCID in the past 7 years are generally consistent with previous findings from the population-based studies in the United States during the 1970s to 1990s that reported a higher SCI incidence in males, among those 16 to 30 years of age, among blacks (particularly violence-related SCIs), and during weekends and warmer months.6,7, 9, 10, 16, 25-27 The present study findings of substantial variations of specific etiologies of injury by age, sex, race/ethnicity, day, and month further highlight the need for prevention strategies to be tailored to the targeted population and major causes of SCI to increase their impact on reducing the incidence of SCI. The strongest efforts at preventing SCI should focus on young males and automobile crashes. Prevention targeting blacks must address violence issues. Prevention programs designed for adolescents and young adults should address risk-taking behaviors, whereas prevention programs for the elderly should be aimed at falls.

The observation of a strong relationship between etiologies and level/completeness of injury also provides insight regarding the mechanisms of injury, which will aid in the design of equipment and other safety measures to reduce the incidence of SCI. In addition to personal characteristics and mechanical causes, there are behavioral and environmental factors that need to be considered in the development and coordination of prevention efforts, for instance, alcohol use, seatbelt use, distracted driving, road conditions, laws and law enforcement, which are beyond the scope of this study.

Conclusion

Prevention of SCI must be multifaceted and consider personal characteristics and mechanical causes as well as the social and political context of the injury. As prevention programs likely compete for recognition of benefits and costs against other regional and national agendas and resource priorities, strategies should be aimed at the targeted population and major causes to have the greatest impact on reducing the incidence of SCI. The present study sheds light on recent statistics of the etiology of SCIs in the United States with the hope of developing and implementing cost-effective prevention programs in the years to come.

References

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