Spinal cord stimulation for chronic pain: who it is for and how it works

Cambridge University Hospitals describes spinal cord stimulation systems, sometimes known as neuromodulation, as delivering small electrical fields to the spinal cord. These electrical fields mask areas of pain by changing the pain messages the body sends to the brain. It can reduce pain in conditions such as failed back surgery syndrome, neuropathic pain and complex regional pain syndrome, and the leaflet says it is effective in five to seven out of ten cases.

The system has three parts: a lead placed in the epidural space in the spine, a battery device implanted in the buttock or abdominal wall that powers the stimulation, and a handheld controller the patient uses once the system is set up. There are low frequency systems, which produce a tingling sensation in the painful area, and sub-threshold systems, which are usually not felt.

NICE technology appraisal TA159 says spinal cord stimulation is recommended as a treatment option for adults with chronic pain of neuropathic origin who continue to experience chronic pain measuring at least 50 mm on a 0 to 100 mm visual analogue scale for at least 6 months despite appropriate conventional medical management, and who have had a successful trial of stimulation as part of the assessment.

NICE does not recommend it for chronic pain of ischaemic origin except in research, although people already using it for ischaemic pain should have the option to continue. It says SCS should be provided only after assessment by a multidisciplinary team experienced in chronic pain assessment and in providing ongoing monitoring and support for people with SCS devices. Assessments should take account of disabilities and communication difficulties to ensure equality of access, and if systems are equally suitable the least costly should be used.

The Cambridge leaflet says SCS is reserved for patients with severe chronic pain that limits daily life and who have already tried all reasonable conservative therapies, such as medications, TENS, physiotherapy and injections. To be considered you must be 18 or over, have a diagnosis such as failed back surgery syndrome, complex regional pain syndrome or neuropathic pain, have moderate to severe chronic pain, have tried and not responded to conservative treatments, be willing to stop or reduce excessive medication and use pain management strategies, and be able to manage the technical demands of the equipment.

It lists reasons SCS may not be appropriate, including pain that will not benefit (for example due to arthritis or spinal instability), widespread pain beyond the area a system can cover, anatomical problems, active infection, some chronic medical or psychiatric illnesses, very high or low body mass index, excessive alcohol or drug use and allergy to nickel or device components.

People are assessed by a doctor, a nurse specialist and a psychologist. The psychology assessment looks at the impact of chronic pain on activities, mood, relationships and sleep, and explores expectations of SCS and how you would feel if it did not work. The multidisciplinary team meets to decide whether you meet the criteria to proceed on the pathway.

In the Cambridge pathway the trial is performed on the table during the procedure: leads are placed in the epidural space at the desired level and therapy is started, and you may be asked whether you feel a pins-and-needles type sensation. If the trial is successful you proceed to the permanent implant, which involves inserting the rechargeable battery under sedation through a small incision in the buttock or abdomen. The therapy is left switched off for 1 week to allow the wound to heal. Because pathways differ between hospitals, ask your own team how their trial is arranged.

The leaflet lists risks including a painful battery or connection site, infection (less than five in 100 people) which may need removal of the whole system, bleeding, severe headache, leads that move or stop working, unpleasant stimulation, failure to capture the area of pain or no pain relief, allergic reaction, decrease in pain relief with time, and nerve damage causing pain, numbness or weakness. Paralysis is described as extremely rare, with two patients in one million.

Some activities may need to be avoided for the first 12 weeks to stop leads moving. You must tell any future surgeon and anaesthetist you have SCS, because they need to change the equipment they use. Depending on the device, an MRI scan may not be possible, although CT scans and X-rays are allowed. Stimulators may activate airport detectors and shop security devices, and strong magnets can switch the stimulator off. You should not drive with the device on if you have sub-threshold therapy, because sudden increases in stimulation may interfere with driving.

The leaflet says the battery lasts on average somewhere between 10 and 12 years depending on type and use, and replacement is a simple day surgery procedure. Follow-up is by the specialist team and clinic appointments are booked after the implant.

SCS does not cure the cause of pain. Cambridge describes it as one part of a treatment strategy, so physiotherapy, psychological support and medicines may continue. Pain relief can decrease with time, and some people have the system removed or revised. A frank discussion with the pain team before the trial about what level of improvement would be worthwhile helps set expectations.

NICE guidance applies to NHS commissioning in England, and access depends on local pain service pathways and funding approvals. Private pain clinics may offer SCS, but NICE and the Cambridge leaflet both emphasise the importance of multidisciplinary assessment, psychological assessment and long-term follow-up, which are reasonable things to check with any provider, together with who will look after the device in the future.