What are the similarities and differences of TENS, FES, and spinal cord stimulation?
Neurostimulation is changing the face of neurological rehabilitation as we know it. It has a wide variety of uses including pain relief, treatment for psychiatric diseases and more recently to treat movement disorders such a multiple sclerosis and spinal cord injury (SCI), writes Tom Elphick, SpinalCure community ambassador.
When used over the skin, this treatment can be very safe.
Here we take a look at two common forms of stimulation and the developing area of spinal cord stimulation.
What is neurostimulation?
Neurostimulation changes the activity of the nerves in your body using small electrical currents to produce a response in the body.
These currents are delivered either directly to the nerves, via implanted electrodes, or indirectly by placing the electrodes over the skin. The electrical current excites the nerves and causes them to activate.
A nerve is an excitable cell meaning when an electrical current is delivered, it produces a signal to neighbouring nerves to also become excited.
The aim of neurostimulation is to harness these nerve responses and use them therapeutically or in rehabilitation. Using stimulation, we can control to a degree the way the nervous system is working which can help improve outcomes.
Nerve signals travel in two directions; 1) to the muscles to produce movement or 2) to the brain to be interpreted as sensation. We can use this to activate muscles or reduce pain. We can use different types of stimulation to achieve these varied outcomes.
You may have heard or read about some of different forms of neurostimulation including FES, TENS, or transcutaneous spinal cord stimulation or neurostimulation. But what are they and how are they different from one another?
Transcutaneous Electrical Nerve Stimulation (TENS)
TENS is commonly used to treat chronic or neuropathic pain in people with SCI [1].
How it is used
In TENS, a small amount of current is delivered to the skin and causes a tingling sensation where the electrode is. When nerves are only slightly activated, they produce this tingling sensation. These tingling signals are sent to the brain and trick it into forgetting that pain signals are also coming from the body.
Does it work?
The theory is called the “gateway theory of pain” and was theorised by Melzack and Wall in 1965 [2]. Evidence to show that TENS really works is limited and systematic review of the literature (we spoke about that here) shows that it may not be as effective as hoped [3,4]. TENS has also been used to try and reduce spasticity in people with SCI but it may be no different to other neurostimulation techniques [5].
Functional Electrical Stimulation (FES)
FES has been used to help people with SCI regain bladder and bowel function and restore sexual function [6].
How it works
In FES, a high amount of current is delivered to the skin. The current is large enough to activate the muscles beneath the skin to contract and produce movement. This helps bowel movement or bladder contraction to expel their contents and retrain the muscles to work as before.
It is also commonly used in people with complete SCI to maintain cardiovascular fitness [7].
FES-driven cycling is a technique where people with paralysed arms and/or legs do cycling movements with the help of FES. The pads are all connected to a computer which stimulates them to contract at different times, like they normally would during cycling. Because the current is large enough to make the muscles contract, the participant’s leg muscles move the machine. Regular exercise helps maintain muscle bulk and improve cardiovascular fitness, both of which are important to maintain especially after SCI.
Spinal cord stimulation
Spinal cord stimulation (or neurostimulation) is the newest form of neurostimulation therapy. It is being used to retrain muscles and restore walking function, hand function, spasticity and bladder/bowel function in people with SCI.
How it is different
Electrodes are placed around the spinal cord area, not over the muscles or nerves in limbs.
How it is used
In spinal cord stimulation, pads are placed either directly next to the nerves and have to be implanted with surgery or they can be placed on the skin over the spine.
The current that is delivered via these electrodes excites the nerves that are close to the spinal cord.
When these nerves are excited, they send their signals into the spinal cord. Within the spinal cord the signals activate many other nerves inside the spinal cord and activate pathways inside the spinal cord called central pattern generators. These are existing nerve pathways that control some ‘ingrained’ functions like walking. When they are activated, we can perform the action without really thinking about it (it’s why we can walk and text at the same time).
SpinalCure is funding a human trial with transcutaneous spinal cord stimulation i.e. on the skin, due to its safety and potential to make a real difference to people with spinal cord injury. It is also a much more affordable option to roll out into the community.
Does it work?
Ongoing research is still trying to understand what exactly happens within the spinal cord but the results from recent studies are promising. They show that people with SCI are able to produce walking-like movements with invasive and non-invasive spinal cord stimulation [8].
Our current world-first randomised control trial using transcutaneous (over the skin) spinal cord stimulation in people with SCI hopes to answer some of these questions and is a game changer in terms of SCI rehabilitation. Here we hope that spinal cord stimulation will help stimulate neuroplasticity which makes recovery more permanent.
Research is always progressing to find better ways to use these neurostimulation techniques to support relief, rehabilitation, and recovery for people with SCI.
Our Scientific Advisory Panel believes that transcutaneous spinal cord stimulation could be a game-changer, and are aiming to expand our trials and studies around Australia. If successful, we could get the evidence needed to get neurostimulation devices approved for use by people with SCIs around Australia.
Read more
Project Spark – aiming to expand spinal cord neurostimulation research around Australia
References:
[1] Celik, E.C., Erhan, B., Gunduz, B. and Lakse, E., 2013. The effect of low-frequency TENS in the treatment of neuropathic pain in patients with spinal cord injury. Spinal cord, 51(4), pp.334-337.
[2] Melzack, R. and Wall, P.D., 1965. Pain mechanisms: a new theory. Science, 150(3699), pp.971-979.
[3] Gibson, W., Wand, B.M. and O’Connell, N.E., 2017. Transcutaneous electrical nerve stimulation (TENS) for neuropathic pain in adults. Cochrane Database of Systematic Reviews, (9).
[4] Gibson, W., Wand, B.M., Meads, C., Catley, M.J. and O’Connell, N.E., 2019. Transcutaneous electrical nerve stimulation (TENS) for chronic pain‐an overview of Cochrane Reviews. Cochrane Database of Systematic Reviews, (4).
[5] Sivaramakrishnan, A., Solomon, J.M. and Manikandan, N., 2018. Comparison of transcutaneous electrical nerve stimulation (TENS) and functional electrical stimulation (FES) for spasticity in spinal cord injury-A pilot randomized cross-over trial. The journal of spinal cord medicine, 41(4), pp.397-406.
[6] Creasey, G.H. and Craggs, M.D., 2012. Functional electrical stimulation for bladder, bowel, and sexual function. Handbook of clinical neurology, 109, pp.247-257.
[7] Ye, G., Grabke, E.P., Pakosh, M., Furlan, J.C. and Masani, K., 2021. Clinical Benefits and System Design of FES-rowing Exercise for Rehabilitation of Individuals with Spinal Cord Injury: A Systematic Review. Archives of Physical Medicine and Rehabilitation.
[8] Donovan, J., Forrest, G., Linsenmeyer, T. and Kirshblum, S., 2021. Spinal Cord Stimulation After Spinal Cord Injury: Promising Multisystem Effects. Current Physical Medicine and Rehabilitation Reports, pp.1-9.