Spinal Cord Stimulation
Spinal Cord Stimulation(SCS) or neuromodulation can be used to treat intractable pain conditions that have not responded to more conservative approaches such as medication, surgery, manual therapy, exercise or psychological interventions. Despite being considered minimally invasive, it is not without risk and is considerably expensive. The technology is evolving at a fast pace, with newer approaches targeting different anatomical structures and using differing electrostimulation. Despite this however, the overall success rate associated with the use of the technique has not improved over recent times. (1)
What does it involve?
There are several different types of SCSs but generally it involves the placement of specialised electrodes inserted into the epidural space or around the dorsal root ganglion. The electrodes generate electrical fields between them and the change in charge influences the nervous tissue in the vicinity. It is thought to work by several mechanisms, with some reference to Melzack and Wall’s gate control theory. Areas of the nervous system known to be affected in successful SCS stimulation include the dorsal columns of the spinal cord, supraspinal regions and higher order processing within regions of the cortex. Other, more recently reported effects of SCS have been identified in glial cells and descending modulatory systems. Despite a great deal of research on the topic, it is fair to say that the exact mechanisms regarding the efficacy of SCS are still fairly hazy (2)
On a more practical note, patients undergo a temporary trial of stimulation to see if it is likely to be helpful and if the trial is deemed successful, can go on to have a permanent system implanted. Once the electrodes are in place, the battery pack is implanted under the skin, usually in the region of the buttocks or waist. The unit is charged and programmed via an external unit that sits close up against the internal unit.
What are the indications?
Its main use is for intractable pain conditions. Because of the invasive and expensive nature of SCS, it is not used unless the indications for it are clear and all other approaches have been exhausted. The patients who is most often used for are often in debilitating pain and experience a great deal of associated suffering and disability. This is not an approach for your garden variety back pain! Neuropathic pain is the most common indication and some of the conditions include:
- Failed back surgery syndrome – chronic back pain following any type of invasive lumbar surgery such as laminectomy or fusion surgery.
- Chronic Regional Pain Syndrome (CRPS) of a single limb
- Chronic migraines
- Chronic pelvic pain
Does it work?
To answer this question, first we need to define “work”. When we are talking about the efficacy of treating chronic pain, the parameters generally used to define success are a reduction of pain on a VAS scale by 30-50%. Understanding expectations are really important in this field as miracle cures and complete pain relief are fairly infrequent. Whilst most people might consider a 30% reduction in pain to be insufficient, on a more functional level it may mean the difference between a person being able to tolerate being in the car for an hour compared to just 10 minutes, or a reduction or cessation of opioid or other medications which carry with them a whole lot of life interfering side effects of their own.
Because it is hard to randomize a study on SCS due to the stimulation being obviously felt in the form of tingling or paresthesia in the stimulated area, the studies are interpreted with caution. Its also important to note that as with the well cited factors that are known to predict the onset of chronic pain, the multifactorial nature of pain means that some people are likely to respond to SCS better than others. Factors that are known to reduce the chances of SCS being effective include depression, PTSD, the presence of third party compensation, misuse of alcohol or other drugs, low self efficacy and other evidence of poor coping skills (3, 4).
Without boring you to death with an extensive review of the literature, it would be fair to say that around half of the people implanted with SCS, regardless of the system used, the type of lead placement or the differing use of electrostimulation types (burst, frequencies etc.) achieve a reduction in their pain of between 30 and 50%. This reduction in VAS scores goes hand in hand with increases in function and quality of life. In practice, having a skilled operator is likely to increase the chances of success and reduce complication rates. Additionally, judicious selection of appropriate patients is going to give the best success rates for a particular clinic (1, 4, 5).
In the pain clinic setting, the suffering that often goes hand in hand with neuropathic pain can be almost unquantifiable. Ordinary people who are unlucky enough to be afflicted with this condition in its variable forms tend to say very similar things about their situation and often follow an understandable downward spiral of loss of function and increasing misery. The depression and fear avoidance with movement that frequently accompanies the suffering are the target of the allied health team working with these patients. Whilst they are frequently modifiable to a degree, they are also incredibly understandable given the situation. The desire to have an option to at least try to ease suffering is the obvious rational for the use of SCS in the pain clinic setting, despite its lack of overwhelming efficacy. When it goes well, it changes lives.
1. Sdrulla AD, Guan Y, Raja SN. Spinal Cord Stimulation: Clinical Efficacy and Potential Mechanisms. Pain Pract 2018;18:1048-67.
2. Vallejo R, Bradley K, Kapural L. Spinal Cord Stimulation in Chronic Pain: Mode of Action. Spine (Phila Pa 1976) 2017;42 Suppl 14:S53-60.
3. Blackburn DR, Romers CC, Copeland LA, Lynch W, Nguyen DD, Zeber JE, Hoffman MR. Presurgical Psychological Assessments as Correlates of Effectiveness of Spinal Cord Stimulation for Chronic Pain Reduction. Neuromodulation 2016;19:422-8.
4. Prabhala T, Kumar V, Gruenthal E, Collison C, Prusik J, Owusu S, et al. Use of a Psychological Evaluation Tool as a Predictor of Spinal Cord Stimulation Outcomes. Neuromodulation 2019;22:194-9.
5. Brinzeu A, Cuny E, Fontaine D, Mertens P, Luyet PP, Van den Abeele C, et al. Spinal cord stimulation for chronic refractory pain: Long-term effectiveness and safety data from a multicentre registry. Eur J Pain 2019;23:1031-44.