Invasive Neuromodulation

Techniques

  • Vagus Nerve and autonomic nervous system stimulation (VNS)
  • Dorsal Root Ganglion Stimulation (DRG)
  • Spinal Cord Stimulation (SCS)
  • Neurostimulation Procedure
  • Cortical stimulation
  • Peripheral Neurostimulation
  • Deep brain stimulation (DBS)
  • Intrathecal Baclofen

Vagus Nerve and autonomic nervous system stimulation (VNS)

Vagus Nerve Stimulation is a treatment for a wide variety of indications going from depression, epilepsy to autoimmune disorders, obesity and others such as tinnitus etc.

An electrode is implanted in the neck on the left side surrounding the vagal nerve, which is one of the 12 cranial nerves. Apart from hoarseness, few side effects are noticed with this technique. It is yet unknown whether non-invasive vagus nerve stimulation can predict the success rate of invasive, i.e. surgically implanting vagus nerve stimulation.

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Dorsal Root Ganglion Stimulation (DRG)

Dosal Root Ganglion Stimulation is a special form of invasive neuromodulation in which the electrode is positioned on the entry point of the peripheral nerve in the spine. This is especially effective for Complex Regional Pain Syndrome (CRPS), inguinal pain or pain along the front of the body.

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Spinal Cord Stimulation (SCS)

Spinal cord stimulation (SCS) is a technique used to suppress nerve pain using electrical impulses transmitted via electrodes. The best candidates for this treatment are patients who suffer untreatable chronic pain as a result of irreversible damage to a nerve. Such damage can be caused by severe pressure on the nerve by a herniated disc and despite surgical removal, the pressure persists. To date, this technique has not been used to treat mechanical pain symptoms such as back pain (before or after surgery) or pain as a result from fractures.

This neurostimulation procedure is considered when a patient with nerve pain fails to respond to the non-surgical treatment. Due to the high cost of Spinal Cord Stimulation, the patient’s condition is rigorously evaluated by the neurosurgery team, a clinical psychiatrist and a pain specialist to ensure that the possible candidate meets all the selection criteria.
During the trial period, the neurosurgeon inserts an electrode connected to an external trial stimulator into the spinal cord canal after which the patient will be followed up for at least 4 weeks. During this period, the patient is asked to stay at home and resume his daily activities to test the functioning of the neurostimulator. After 1 to 4 weeks, the effectiveness of the trial neurostimulation will be reassessed. A pain reduction of at least 50% is considered clinically beneficial. If the treatment using the trial stimulator is considered therapeutic, the neurosurgeon will connect the electrode to an internal battery (IPG = Internal Pulse Generator). The IPG allows stimulation of the electrodes to be adjusted remotely for treatment optimisation.

Spinal Cord Stimulation can also be used for some specific movement disorders such as Parkinsons or spasticity.

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Neurostimulation Procedure

This neurostimulation procedure is considered when a patient with nerve pain fails to respond to the classic treatment. Due to the high cost of SCS, the patient’s condition is rigorously evaluated by the neurosurgery team, a clinical psychiatrist and a pain specialist to ensure that the possible candidate meets all the selection criteria.

During the trial period, the neurosurgeon inserts an electrode connected to an external trial stimulator on to the spinal cord canal after which the patient will be followed up for at least 4 weeks. During this period, the patient is asked to stay at home and resume his daily activities to test the functioning of the neurostimulator. After 1 to 4 weeks, the effectiveness of the trial neurostimulation will be reassessed. A pain reduction of at least 50% is considered clinically beneficial. If the treatment using the trial stimulator is considered therapeutic, the neurosurgeon will connect the electrode to an internal battery (IPG = Internal Pulse Generator). The IPG allows stimulation of the electrodes to be adjusted remotely for treatment optimisation.

Spinal cord stimulation can also be used for some specific movement disorders such as Parkinsons or spasticity.

Benefits of Neurostimulation

In principal, the neurostimulation procedure is completely reversible. If results from the trial period show no therapeutic effects, the electrode can be removed. Also, it is possible to perform all routine daily activities including sports after the surgical implant.

Disadvantages of Neurostimulation

The neurostimulation procedure is an expensive treatment. Neurostimulation reduces the intensity of the pain but does not treat the underlying cause. The neurostimulator device is a foreign material in the body and although rare, there is a risk of infection especially in the first weeks after surgery. If an infection occurs, the neurostimulator will be removed. Also, technical problems may occur such as the displacements of contact points. The battery (IPG) of the device has to be regularly replaced through minor surgery. On average, a battery will last 6 to 10 years, depending on the program used for treatment.

Recently new forms of stimulation have been developed that can suppress pain more profoundly than classic tonic stimulation. These new stimulation designs such as burst stimulation are however not reimbursed within the Belgium system in contrast to all other countries in the world (except France).

Cortical stimulation

The cortex cerebri or cerebral cortex consists of cells where information from all over the body and the environment are received, processed and interpreted. A cortical electrode placed on the cerebral cortex can affect the local brain cells electrically. This technique has been successfully applied to combat phantom limb pain and tinnitus. Before a cortical electrode is placed, extensive assessments will be conducted to ensure that the treatment will have a high chance of success.

These invasive neuromodulations involved non-invasive stimulation techniques such as TMS, HD-tDCS or HD-tRNS or a prognostic test to verify whether an implant is worthwhile or not. All in all ⅓ of patients respond very well to the procedure and were virtually cured, ⅓ improve to a certain extend and ⅓ fail to respond irrespective of the target or stimulation design.

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Figure from De Ridder D, Perera S, Vanneste S.: State of the Art: Novel Applications for Cortical Stimulation. Neuromodulation. 2017 Apr;20(3):206-214

Peripheral Neurostimulation

Our whole body is embedded with nerves, some of which are located beyond the spinal cord or brain. Peripheral nerves bring information from the periphery of our body to the brain via the spinal cord. The brain, in return commands the muscles through the peripheral nerves to initiate movement. By placing a small neurostimulation device next to a peripheral nerve, stimulation can be used to combat local pain. Peripheral neurostimulation has been proven to be useful in the treatment of fibromyalgia, headaches and migraines, but also for other diseases.

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Deep brain stimulation (DBS)

Deep brain stimulation (DBS) is a surgical procedure where one or more electrodes are inserted into certain brain areas for electrical stimulation. This form of neuromodulation is used to reduce stiffness, trembling and improve the strength of the limbs. DBS is mainly used in disorders that cause problems with movements, such as Parkinson’s disease, tremor (shaking) and dystonia (abnormal muscle tone). DBS has also been used to treat Huntington’s disease. DBS treats the symptoms and not the underlying cause of the disease.

Medications may help control the symptoms of Parkinson’s disease however, they have been associated with adverse effects. Under these circumstances, the neurologist may consider referring the patient to a neurosurgeon for surgery.

Over the last few years, DBS has been used to treat epilepsy and certain psychiatric disorders (such as depression, obsessive compulsive disorders and Tourette Syndrome). More recently, there have also been studies investigating the effects of DBS on obesity, addiction problems and anorexia nervosa.

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Intrathecal Baclofen

Spasticity is a condition where an increase tension of muscles or muscle groups occur involuntarily. Spasticity can lead to severe pain and functional limitations. There are several possible causes of spasticity. A common cause is trauma or damage to the spinal cord. In addition, there are a number of neurological disorders that may give rise to spasticity: multiple sclerosis, familial spastic paraparesis (Strumpell-Lorraine). Damage to the brain as a result of trauma or oxygen deprivation (at birth or by CVA) can cause spasticity.

Treatment

The main treatment for spasticity is physical therapy. Daily or at least regular mobilization of the limbs with spasticity can reduce the severity that is often associated with pain.

In addition, many patients are treated with various forms of medications such as muscle relaxants (Valium, Myolastan, Epsipam) or GABA agonists (baclofen). Local spasticity in smaller muscle groups is treated using botulinustoxine (Botox).

However, some patients develop increasing spasticity despite therapy or experience side effects from medication. In these patients, the use of GABA agonists (baclofen) administrated in the spinal cord is considered: intrathecal baclofen therapy. Since the duration of action of baclofen in the spinal cord last for just a few hours, it is continuously administered using an internal pump system.

Procedure For Intrathecal Baclofen Therapy

  • Select appropriate patients 
  • Always test baclofen in pill form
  • Trial run with baclofen repeatedly injected into the spinal cord channel via a tube (catheter)
  • Evaluation of the trial by a physiotherapist/physical therapist
  • If results in a positive dose dependent, a pump system is placed

Refilling A Baclofen Pump System

The system has to be refilled every 2 to 3 months via a filler in the middle of the pump. The refilling procedure is conducted by a consultant.