1.1

Introduction

The prevalence of neuropathic pain in spinal cord injury (SCI) patients is estimated at 60% and has a negative impact on their quality of life. SCI neuropathic pain is hard to classify and the therapeutic care offered is sometimes inefficient. Thus, alongside general or local pharmacological treatments, other non-pharmacological strategies, were proposed to the patients.

Among these solutions spinal cord stimulation (SCS) has been used following a new theory concerning the intrinsic mechanisms of pain control , two publications reported the feasibility and efficacy of a conservative and reversible surgery for treating SCI pain.

The first step is the percutaneous implantation of a mono- or quadripolar electrode performed with the aid of fluoroscopy in the posterior epidural space in order for the pacemaker-induced electrical sensations to cover the entire painful area. If at the end of this trial period the patient reports a significant pain-relieving improvement, a permanent implantation will take place. This will be done either percutaneously or through direct skin incision requiring a laminectomy to insert a quadripolar or even octopolar electrode connected to a radio-frequency or totally implantable pacemaker.

The physiological bases for this technique are controversial. They directly come from the “gate control theory of pain” stating that nociceptive unmyelinated afferents are inhibited by stimulation of non-nociceptive myelinated afferents. We will see in the discussion that other mechanisms can be argued.

Since, these initial descriptions several issues are yet unresolved mainly the selection for this techniques’ indications. Forty years after the first publications, we still wonder what the efficacy of this technique is in regards to treating neuropathic pain in SCI patients. Our goal with this work is to find the proper elements to answer this question.

1.2

Material and method

Regarding SCS efficacy, the bibliographical search was conducted with the following keywords in English: chronic neuropathic pain in SCI/human/adult and spinal cord stimulation and in French: douleur chronique chez le blessé médullaire/humain and stimulation médullaire , to which we added neurosurgical management of pain. Eighty-three articles were selected, 36 were analyzed and used for this review.

The quality of each article was assessed using the grid from the French National Health Authority (see general article on methodology).

1.3

Results

Twenty-seven publications on SCS clinical studies were analyzed because they included at least one SCI patient.

Twenty-one of them ( Table 1 ) focused on SCS for chronic pain without the notion of SCI. After reading these publications, we essentially see that this indication is quite rarely found in these series and that the results are quite disappointing, when available at all, around 30 to 40% of success rates for the studies on SCI.

The study with the most SCI patients, Lazorthes et al. , included 101 chronic SCI patients but also very disparate etiologies such as iatrogenic or non-iatrogenic trauma, viral causes or degenerative pathologies. The results are not analyzed specifically.

Regarding the adverse events of this technique a study , not listed in Table 1 because the number of SCI patients is unknown, reports its experience on 509 electrodes implanted in 350 patients, including 227 with chronic pain, without any major complications. The adverse events listed were: infections 3.4% of patients, movement of the electrodes for 1.1% of patients or spinal irritation due to a lateralization of the electrode, material damage and loss of CSF fluid. These are the main adverse events found in the literature with the addition of epidural hematoma such as in the case reported by Franzini et al. thus proving the feasibility of this technique.

Other authors studied this technique for treating chronic pain in SCI patients whether their injury was traumatic or not. We found five publications that met these criteria.

Buchhaas et al. in his study report SCS performed on seven traumatic SCI paraplegic patients with chronic neuropathic pain. The results were excellent in six patients with a 6-year retrospective follow-up. The results are deemed even better since the vegetative components predominated.

Tasker et al. conducted a study on 127 SCI patients with chronic pain, 65% were traumatic SCI patients, 35 of them benefited from SCS (28% of the total number of patients). This work analyzes the results in terms of injury level, complete or incomplete SCI and type of pain. Out of these 35 patients, 24 had incomplete SCI. The three most common types of pain in the 127 patients were characterized as: steady, intermittent, and evoked (allodynia, hyperpathia or hyperesthesia). The type of pain is not related to the level of injury.

The results are good (with a significant pain decrease of at least 50%) over 1 year for the incomplete SCI patients that report a steady pain in 27% of cases. They are never good for complete SCI patients, or for intermittent or evoked pain. According to the authors, incomplete SCI patients at T10-L2 level with steady lesions would be the ideal candidates for SCS.

Cioni et al. report in their study their SCS experience on 25 SCI patients with chronic pain including 15 post-traumatic SCI patient. Age, sex, level of injury, neurological profile, localization and type of pain are all known data. Nineteen incomplete SCI patients. After a trial period from one to 3 weeks, nine patients (40.9%) who reported at least a 50% pain decrease were definitely implanted. Unfortunately, after a 3-year follow-up, the satisfaction rate drops to 18.2%. The authors conclude that the positive prognostic factors to this stimulation are spasm or contracture pain, incomplete SCI and thoracic level of injury.

Richardson tested 20 SCI patients with chronic pain. The characteristics in terms of injury level, complete or incomplete SCI or type of pain were not available. Seventy-five percent were implanted with a good initial result but after 1 year, only 40% still report an improvement of their chronic pain. The authors insist on the behavior and personality issues that can interfere with SCS. Finally, they bring up the problems encountered with the material and other issues that make the procedure more complicated.

Warms et al. conducted a study on 1100 SCI patients in the United States, focusing on pain-relieving treatments, pharmacological or not, by way of two surveys sent by regular mail. Between February 1997 and July 1998 they received 308 answers. Then, between August 1998 and June 2000 they received 163 answers. The patients reported using SCS respectively at 11.7% for the first survey and 5.5% for the second one, making it the most used surgical method. On a Visual Analog pain Scale (VAS) going from 1 to 5, the scores from both surveys are weak respectively 1.67 and 1.78. Regarding pharmacological treatments, the reported scores for opioids are 3.08 and 3.47. For non-pharmacological treatments physiotherapy is scored at 2.87 and 3.06. However, this results can not be statistically compared since patients could use several concomitant treatments (4 in average). Thus, to get a better idea of the efficacy of SCS on chronic SCI pain, the authors evaluated the continuous use, it is reported at 22.2% for the nine implanted patients (seven patients gave up this technique).

1.4

Discussion

During this literature review, we did not find any study that brought a sufficient level of proof regarding the use of SCS in this indication: neuropathic pain of SCI patients. A Cochrane review of 2004 listed two level three studies promoting the use of SCS for chronic pain but not for the indication listed above.

Most publications reported in our work were retrospective studies (except Shimoji et al. and Richardson ) were the etiologies are disparate, the pain characteristics badly defined and the inclusion or exclusion criteria are not often available. The cohort study of Warms et al. did not focus specifically on the impact of SCS in the chronic pain of SCI patients but rather on the pain-relieving treatments used by SCI patients. Thus, the criteria for using SCS are not available, no data is found on the specific characteristics of the stimulated patients (injury level, complete or incomplete and type of pain).

A panel of 166 experts, mainly Physical Medicine and Rehabilitation (PM&R) specialists (92%), were surveyed during the SOFMER conference in October 2007 (116 attendees and 50 voted on the SOFMER website). They were asked about their clinical experience on pain-relieving techniques (see details in Appendix 1 ). To the question: Do you propose this technique? 41.61% answered “yes”. To the question: For which indication, according to the type of pain: 26.67% for steady pain and 17.58% for intermittent pain (electric shocks). According to the level of injury: 10.09% cervical, 10.09 high thoracic, 16.38% low thoracic and 10.09% for lumbosacral. According to the degree of injury, 22.57% for complete SCI and 32.08% for incomplete SCI.

Needless to say that the use of this technique, still proposed actually to SCI patients for chronic neuropathic pain, is badly defined.

In light of the answers received, further studies should be conducted to better define the use of this technique and its potential applications. Two types of studies seem necessary.

First, studies that would focus on the role of SCS. Some authors bring up the “gate control theory” but it is certainly not enough to prove the efficacy of the technique. Hunter and Ashby studied the segmental effects of SCS but its impact might be wider even supraspinal through the activation of the inhibiting system found in the medullary subnucleous reticularis dorsalis and stemming from the adjacent cuneate nucleus . Furthermore a sympatholytic impact was brought up . Finally, the biochemical mediation still needs to be further delimited.

Secondly, more clinical studies that would define subgroups that would have a good chance of responding positively to SCS. Most authors tend to agree that complete SCI patients cannot benefit from this technique. In fact, it seems that the test has more chances to be positive if it creates parestheses into the stimulated area. It seems also essential to study the pain characteristics. Other elements could be highlighted such as the relevance of combining SCS with a pharmacological treatment as suggested by Meyerson et al. (not focusing on SCI patients but on peripheral neuropathies) or, as suggested before, associated to a psychological and behavioral treatment.

1.5

Conclusion and recommendations

At the term of our work, if SCS seems to be a technique with a real feasibility, its pain-relieving efficacy on SCI patients is far from being established and this after nearly 40 years of use. However, the debilitating nature of neuropathic pain, the lack of efficient treatments available and the good feasibility of this technique could justify further studies. To this day no recommendation can be made in regards to the level of proof found in the literature.

Appendix 1

Answers to the question asked to the 116 physicians attending the SOFMER conference and the 50 others that answered on the SOFMER website

Do you propose spinal cord stimulation to your spinal cord injury patients suffering from chronic neuropathic pain?

• •
  

  dnk: 4,82%;

  
  
• •
  

  yes: 41,61%;

  
  
• •
  

  no: 53,57%.

• •
  

  dnk: 18,48%;

  
  
• •
  

  steady: 26,67%;

  
  
• •
  

  intermittent: 17,58%.

• •
  

  dnk: 18,48%;

  
  
• •
  

  cervical: 10,09%;

  
  
• •
  

  high thoracic (> Th6): 10,09%;

  
  
• •
  

  low thoracic: 16,38%;

  
  
• •
  

  lumbosacral: 10,09%.

• •
  

  dnk: 18,48%;

  
  
• •
  

  complete SCI: 22,57%;

  
  
• •
  

  incomplete SCI: 32,06%.

2.1

Introduction

La douleur du blessé médullaire, toujours source d’altération de la qualité de vie, aurait une prévalence estimée à 60 %. Elle pose de nombreux problèmes de nosologie et de prise en charge thérapeutique. Aussi à côté de solutions pharmacologiques générales ou locorégionales, d’autres stratégies, non pharmacologiques ont pu être proposées.

Parmi ces solutions les stimulations médullaires sont utilisées depuis que, dans les suites d’une nouvelle théorie concernant les mécanismes intrinsèques de contrôle de la douleur , deux publications aient rapporté la faisabilité et l’efficacité d’une technique chirurgicale conservatrice et réversible dans le traitement de cette douleur.

Il s’agit dans un premier temps d’implanter de façon percutanée sous guidage à l’amplificateur de brillance une électrode mono- ou quadripolaire dans l’espace épidural postérieur de telle sorte que les sensations électriques induites par un pacemaker recouvrent la topographie de la zone douloureuse. Si au terme d’une période test le patient signale une atténuation significative, une implantation définitive en percutanée ou par technique ouverte nécessitant une laminectomie a minima insère une électrode quadri, voire octopolaire reliée à un pacemaker à radiofréquence ou totalement implantable.

Les bases physiologiques qui sous-tendent cette technique sont controversées. Si elle dérive directement de la théorie du gate control du fait d’une possible stimulation des fibres sensitives de gros calibre regroupées au sein des cordons postérieurs et donc une inhibition des fibres C, nous verrons dans la discussion que d’autres mécanismes sont discutables.

Depuis ces descriptions initiales, plusieurs problèmes demeurent et notamment celui de la sélection de ses indications. Quarante années après ces premières publications, la question demeure en ce qui concerne la douleur du blessé médullaire : quelle est l’efficacité de cette technique ? C’est l’objectif de ce travail que de chercher des éléments de réponse à cette question.

2.2

Matériel et méthode

En ce qui concerne l’efficacité des stimulations médullaire, la recherche bibliographique a été initiée avec pour mots clés : chronic neuropathic pain in SCI/human/adult and spinal cord stimulation et en français douleur chronique chez le blessé médullaire/humain et stimulation médullaire, auxquels nous avons ajouté neurosurgical management of pain . Quatre-vingt-trois articles ont été retenus, 36 sont analysés et utilisés dans cette revue.

La qualité de chaque article est évaluée à l’aide de la grille de la Haute Autorité (voir article général sur la méthodologie).

2.3

Résultats

Vingt-sept publications rapportant des essais de stimulations médullaires sont étudiées parce qu’elles comportent au moins une atteinte médullaire.

Vingt et un d’entre-elles ( Tableau 1 ) s’intéressent à la stimulation médullaire dans le cadre de la douleur chronique sans centrer la problématique sur le blessé médullaire. À la lecture de ces travaux, on retient essentiellement que cette indication n’est pas fréquente dans ces séries, que les résultats sont plutôt décevants, quand on peut les extraire, aux alentours de 30 à 40 % de succès dans ces études pour les atteintes médullaires.

Tableau 1

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