Spinal Cord Stimulation: Why the Trial Comes First

Spinal cord stimulation places electrodes in the epidural space to deliver current that alters how pain signals are perceived. Neurostimulation therapy was approved in 1989, and it is now a standard option for chronic pain that has not responded to anything else.

It is also the procedure with the most honest success figure in interventional pain, and that figure is the reason the trial exists.

Fifty to seventy percent — and why that number matters

Empire's curriculum states it plainly: the success rate ranges from 50 to 70 percent, so not everybody is going to benefit from this type of procedure.

That is unusually candid for a device-based intervention, and it has a direct consequence. Between three and five patients in ten will not get a useful result — which is precisely why nobody is implanted without a trial first.

The trial is not a formality. It is the mechanism that keeps a permanent implant out of the half of patients it would not help.

What it is used for

Spinal cord stimulation targets chronic intractable pain, particularly where the pain is radicular in nature. The conditions it is used for:

• Failed back surgery syndrome — persistent or recurrent pain following back surgery
• Complex regional pain syndrome, type 1 and type 2
• Peripheral neuropathy, including diabetic neuropathy
• Phantom limb pain, where it works particularly well

What connects them is that all are difficult to treat by other means. This is not an early-stage option.

The selection criteria, and why each one is there

Patient selection for stimulation is stricter than for almost anything else in interventional pain, and each criterion earns its place.

• Pain not associated with malignancy.
• Poor response to conservative treatment, documented for a minimum of six months. Documented, not merely reported.
• Revision surgery is not an option, has low chances of success, or the patient is not a surgical candidate.
• No pacemaker or other medical condition that would contraindicate the device.
• No major psychiatric disorder.
• Willingness to stop inappropriate drug use prior to implantation.
• No related litigation is the usual recommendation.
• Ability to give informed consent.

Several of these are about whether the result can be assessed rather than whether the device will work. A patient in active litigation, or using substances that alter pain reporting, produces a trial result nobody can interpret — and an uninterpretable trial is worse than none, because it leads to an implant placed on bad information.

The trial, and why the patient stays awake

The trial is performed under monitoring — ECG and blood pressure — in a hospital or ambulatory surgical centre.

An introducer needle is passed into the epidural space and electrodes are inserted through it. Leads are most often placed in the mid-section of the spine, around T7 to T10, though this depends on the patient's pain pattern. The battery is connected to the wires to generate current.

Then comes the step that defines the procedure. The position of the electrodes is adjusted until the stimulation covers most of the painful area — and the only way to know whether it does is to ask the patient.

Which is why this is done under local anaesthetic only, with the patient awake and able to report what they feel. There is no substitute for that feedback, and no imaging finding replaces it.

The introducer needle is then removed, the temporary wire secured to the skin with a stitch and covered with a large adhesive dressing.

What counts as a successful trial

The threshold used across neuromodulation is a 50 percent reduction in pain. A patient who achieves that during the trial is a candidate for permanent implantation. One who does not is spared a device that was not going to help.

Recording the baseline properly beforehand, in the same terms, is what makes that judgement possible.

Who does the trial and who does the implant

In most practices these are two different clinicians. Interventional pain physicians typically perform the trial and refer permanent implantation to a neurosurgeon or spinal surgeon, though a smaller number of interventional pain physicians perform the implants themselves.

Both the trial and the implantation are reimbursed by Medicare and by private insurance.

It is worth being aware of an incentive that sits inside that arrangement: the trial takes considerably less time than the permanent implantation while reimbursing comparatively well. That is a fact about the payment structure rather than a criticism of anyone, but it is the sort of thing worth knowing exists when a trial is recommended — and a reason the documented six-month conservative failure requirement matters.

Questions worth asking before a trial

1. Have I genuinely completed six months of documented conservative treatment?
2. Is revision surgery still an option, and has that been properly assessed?
3. What are we measuring, and what is my baseline?
4. What happens if I get 40 percent relief rather than 50?
5. Who performs the permanent implant if the trial succeeds?
6. What is the plan if the trial fails?

That last question is the important one. A trial that fails has still produced useful information — it has ruled out a major intervention. A clinic that has no answer for it has not thought the pathway through.

Where the intrathecal pump fits instead

For some patients an implanted drug delivery system is a better fit than stimulation, and the success figures differ substantially — around 90 percent against stimulation's 50 to 70. The two are not interchangeable, and the choice depends on the pain and the patient rather than on which is more effective in the abstract. That comparison is in intrathecal pump therapy.