Spinal Cord Stimulator Trial

Abstract

Spinal cord stimulation has been used since the 1960s originally based on the gate control theory suggested by Melzack and Wall. This theory suggested that the activation of large A-beta nerves inhibited or “closed the gate” on small pain transmitting A-delta and C fibers (Melzack and Wall, Science 150(3699):971–979, 1965). The multifactorial mechanisms behind neuromodulation are a growing topic of research with dorsal horn suppression, A-beta inhibition, GABA activity, improved perfusion, and supraspinal action on descending inhibitory pathways all being implicated (North et al., Neurosurgery 57(5):990–996, 2005; Weigel et al., Pain Physician 18(2):185–194, 2015).

Spinal cord stimulation (SCS) systems are made up of two parts: implanted leads and a programmable pulse generator. Leads are placed at spinal cord levels corresponding to the patient’s pain, and with traditional SCS systems placement can be confirmed via patient feedback in the form of paresthesias at the target site. Newer forms of SCS (burst, high-frequency, differential target multiplex, etc.) do not generally cause paresthesias and so lead implantation is based on anatomy. Pulse width, frequency, and amplitude can be programmed on the pulse generator to achieve desired results.

SCS is used to treat conditions such as complex regional pain syndrome, failed back surgery syndrome, chronic limb and trunk pain, peripheral neuropathy, diabetic neuropathy, and pain ischemic vascular disease. Patient selection is paramount and a thorough assessment focusing on coagulation status, infection risk, compatibility with other implanted devices such as cardiac pacemakers and defibrillators, and spinal imaging must be performed. Patients who are offered SCS have usually failed most other more conservative treatments and so the treating physician must have frank discussions with the patient regarding expectations.

Once a patient is selected the first step is a SCS trial to test pain control before permanent implantation. This is routinely done under fluoroscopic guidance in the outpatient setting. Temporary leads are placed in the epidural space percutaneous and routed to an external pulse generator. Trials typically last 3–7 days and is considered successful if resulting in ≥50% pain relief and improved activity (Deer et al., Neuromodulation 17(6):515–550, 2014). If successful, permanent leads and pulse generator are implanted after a period of observation to ensure that no infection has formed.

Complications related to hardware dysfunction such as lead migration or fracture are common and can manifest as abnormal stimulation. Less common complications include infection, spinal epidural hematoma, and dural puncture.