Chronic pain

Spinal Cord Stimulation Therapy

History of spinal cord stimulation therapy

Spinal cord stimulation therapy has a long history, having been used in countries other than Japan since around 1960. It was first used in Japan from around 1970, and since 1999, fully implantable generators have been covered by health insurance. Internationally, generators are implanted in around 20,000 people each year, but in Japan they have only been used in a total of around 5,000 people so far, and domestic awareness of this method is low. Recent developments and advances in treatment devices have improved their safety and decreased the burden on patients, and the number of individuals undergoing this treatment in Japan is increasing.

Principles

When pain is felt in the arms or legs and transmitted via the nerves, there is a barrier in the spinal cord to the transmission of this pain to the brain, and this treatment method regulates the pain at this point. A weak electrical stimulus is applied to the spinal cord so that a tingling sensation is felt at the same location as the pain, and this is regulated to relieve the pain.

Effect

Since spinal cord stimulation therapy does not remove the cause of the pain, its aim is to relieve pain rather than to eliminate it completely. Over half of patients experience pain relief of at least 50%, enabling them to reduce the dose and number of types of drugs they take, thus improving their everyday lives.

Limitations

Spinal cord stimulation therapy is not effective against all types of pain and can only be expected to work on limited types. Even for types of pain where it does work, its effectiveness declines over the long term.

Spinal cord stimulation therapy is not effective against pain due to psychological or social factors such as stress and social background.

Practical use of spinal cord stimulation surgery

Trial surgery (test stimulation)

Around one week of hospitalization is required.

Patients are admitted to hospital on the day before surgery and undergo the operation the following day.

Surgery is carried out under local anesthetic with the patient lying face down. A needle is inserted into the lower back, and an electrode is slowly inserted through this needle into the epidural space (the space around the dura mater, a protective membrane that covers the spinal cord). X-ray imaging is used to check the distance and direction in which the electrode is advanced. The electrode is soft and about 1.3 mm in diameter. A stimulus is applied to the spinal cord from this electrode to create a tingling sensation at the same site where the pain is felt, which is identified during surgery by asking the patient, in order to place the electrode in the ideal spot.

A generator (around the size of a cigarette packet) that generates the electrical stimulation is then connected to the electrode, and continuous electrical stimulation is applied. The generator is small and light and can be moved freely after surgery. The electrical sensation varies between lying down and standing up, and patients are therefore able to switch between stimuli and to regulate their intensity in a manner that feels right to them. Pain relief starts to be felt from around three days after surgery. In patients who respond well, it feels as if the pain has decreased to around 20-50% of its maximum severity, and their everyday lives improve.

As doctors, we regard spinal cord stimulation therapy as effective if the patient feels that their pain has improved by 50% or more, or to put it another way, if it is less than half as bad as it was at its most severe. Other important factors include whether or not the patient experiences the tingling sensation as uncomfortable.

The electrode is removed after around seven days’ stimulation. The pain relief obtained from electrical stimulation normally persists for 1-6 months after electrode removal.

Normally, patients undergo trial surgery (test stimulation) first to judge the effect of spinal cord stimulation therapy.

Site of electrode insertion

Generator implantation

Spinal cord stimulation therapy

Generator implantation surgery

Once the electrode has been removed, the effect of electrical stimulation decreases over time. Patients who want to undergo repeated spinal cord stimulation then have a generator implanted in addition to the electrode in the spinal cord. The electrode is implanted in exactly the same way as for test stimulation. Unlike test stimulation, however, the generator is also implanted inside the body. This generator is small and is implanted in a fatty area such as the flank or buttocks. After it has been implanted, the stimulation is adjusted in different ways to allow for factors such as the way the pain is felt and the body’s orientation, which can be done externally to the body. The stimulus method is adjusted in accordance with the way it is felt by patients, with the aim of relieving the pain. The generator can be controlled externally by the patient himself or herself, who can regulate the intensity of stimulation and adjust it to the most comfortable conditions.

The current that flows from the generator after implantation is very weak, meaning that there is no possibility of it causing an electric shock or noise. Nor does this current exert any control over the patient’s own actions or emotions. It may be possible to feel a bump deep inside the implantation site.

Complications

The electrode is inserted on the outside of the dura mater membrane covering the spinal cord, but since the electrode is a foreign body inside the patient, a rejection reaction, infection, or other reaction may appear. The large number of blood vessels at the electrode insertion site means that bleeding may also occur. If bleeding is severe, it may compress the spinal cord or nerves and cause damage. Potential mechanical malfunctions include the electrode slipping out of position and broken wires. These complications are extremely rare, but they do occasionally occur, and the possibility of their occurrence is not 0%. The doctor in charge will provide a full explanation before surgery.

Postoperative lifestyle

Patients are asked to avoid vigorous exercise for a short time after the operation, but before long, they can return to their usual lifestyle without restrictions. Patients who have undergone spinal cord stimulation therapy can operate the generator themselves, and they should make their own adjustments in accordance with how severe the pain is. Once they have become accustomed to the stimulation, they can also adjust their medication in consultation with the doctor in charge.

MRI scanners used to diagnose disease may cause the implanted generator to malfunction. Today, devices other than MRI scanners can be used for diagnosis, so the first thing is to tell the doctor that you have had a generator implanted. If necessary, doctors will communicate with each other to discuss how this can be dealt with. Some devices that can be used with MRI scanners have become available since January 2014.

Generator replacement

The generator for spinal cord stimulation therapy contains a battery. This runs down as a result of continued everyday electrical stimulation and may ultimately require replacement. Today, rechargeable generators are available, and regular recharging means that the frequency with which they must be replaced varies depending on the type of generator implanted and the stimulation conditions. Details are given during the explanation provided before surgery.

Notes

Spinal cord stimulation therapy is not the “last hope” for chronic pain. We are unable to treat patients for whom all other forms of treatment have failed and who are looking to try it as a last resort.

Treatment for chronic pain is carried out according to a set of well-defined steps. After a careful medical history and examinations, the first treatments used are drug therapy and nerve block. Even patients who have already been treated at other hospitals cannot immediately receive spinal cord stimulation therapy. Whether or not this treatment is appropriate will only be considered after medication has been adjusted and nerve block therapy has been reviewed in an anesthesiology pain clinic.

The key feature of spinal cord stimulation treatment is that patients are able to vary the intensity of stimulation and other factors for themselves in accordance with the severity of their pain. This means that patients who are unable to adjust their generator themselves, such as those suffering from dementia, cannot be considered for this treatment.

We work together with pain specialists in the Department of Anesthesiology to offer effective spinal cord stimulation therapy, in conjunction with oral medication and other methods of treating pain.

Generator implantation

Generator and flow of stimulation

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