The changing face of neuromodulation

Neurostimulation is a type of treatment for chronic pain and some neurological disorders.

Neurostimulation uses precise, targeted electrical stimulation to cause modulation of the nervous system. This changes the way the body perceives pain signals, and can lessen the experience of pain.

In the past, neurostimulation has been used mainly for the management of chronic neuropathic pain. However, new applications for neurostimulation techniques may provide hope for people with epilepsy, Parkinsonian movement disorders and some functional disorders.

History of Neuromodulation

The broad term ‘neuromodulation’ encompasses a number of techniques, including spinal cord stimulation (SCS), peripheral nerve stimulation (PNS), sacral root stimulation, motor cortex stimulation (MCS) and deep brain stimulation (DBS). See below for more information about each of these.

Spinal cord stimulation and peripheral nerve stimulation were the first neuromodulation techniques to be developed. They were first employed for the treatment of neuropathic pain in 1967.

The technique of neuromodulation is based on something called the ‘gate-control’ theory of pain. According to this theory, pain is caused by harmful stimuli at nerve endings. However, in the spinal cord the body has a ‘gate’ which can be shut to stop the flow of pain signals along the nerves. This prevents the pain signals from being received by the brain. It is possible to activate this gate, and close it, by stimulating other nerves with electrical signals (neurostimulation). The sensation of pain is then masked by a feeling of altered sensation called paraesthesia, much like pins and needles.

In practice, neurostimulation techniques were found to be particularly good at controlling a type of pain called neuropathic pain. This is pain due to damage to nerve fibres which is often very difficult to treat using normal pain-relieving medications.

Neurostimulation is particularly helpful in patients with neuropathic pain because it is reversible. This is in contrast to some other surgical pain treatments including neurectomy, rhizotomy and sympathectomy, which are permanent.

Over time, computer modelling and an improved understanding of how pain works have allowed refinement of traditional neuromodulation techniques, as well as development of new applications for the technology.

Current Research and New Applications

Spinal cord stimulation

Spinal cord stimulation devices have been in use for almost forty years. However, only recently has their true potential begun to be understood.

Traditionally, spinal cord stimulation was used in the management of chronic, non-malignant (non-cancerous) neuropathic pain. However, spinal cord stimulation may also be used in the management of the following conditions:

• Peripheral nerve injuries: peripheral neuropathies or phantom limb pain
• Failed back surgery syndrome (FBSS)
• Complex regional pain syndromes (CRPS)
• Ischaemic pain of peripheral vascular disease or cardiovascular disease (angina pectoris)

In recent years, the potential role of spinal cord stimulation devices in the management of conditions such as urinary incontinence (urge incontinence), interstitial cystitis and occipital neuralgia has also been studied.

Overall, approximately 15 000 patients worldwide are now treated with spinal cord stimulation each year. This is probably only a small fraction of the total number of patients who could benefit from these techniques.

Peripheral nerve stimulation

Implanted peripheral nerve stimulation devices are used in the management of peripheral neuropathic pain (that is, pain arising from a nerve outside the spinal cord).

A new application for peripheral nerve stimulation devices has been developed in the form of vagal nerve stimulation. This is the electrical stimulation of one of the nerves in the body which regulates the autonomic (non-voluntary) functions such as heart rate and digestion. Stimulation of this nerve has been found to be helpful in the treatment of some people with epilepsy or depression.

Deep brain stimulation

While originally developed for the treatment of epilepsy, deep brain stimulation is now used mainly for management of Parkinson’s-related movement disorders. One major advantage of this technique over more traditional neurosurgical interventions (eg. thalamotomy) is its reversibility.

Excitingly, research continues into the possibility that early intervention with deep brain stimulation may even slow the progression of Parkinson’s disease.

Motor cortex stimulation

Stimulation of the motor cortex (the part of the brain which controls movements) for pain relief is practiced only in specialised centres. However, motor cortex stimulation may have a role in the management of some special pain syndromes such as postherpetic neuralgia, spinal cord injury, limb stump pain, or trigeminal neuralgia.

Despite this wide variety of clinical applications, the vast majority (85%) of neurostimulation electrodes are currently used in traditional spinal cord stimulation or open extremity peripheral nerve stimulation sites. A wider community awareness of neuromodulation techniques, as well as further research into new applications, will allow more patients to benefit from this technology.