8-A860A-2018-Books-00091Rathmell5e_Ch096-NO CROP-ROUND1

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PART FIVE  METHODS FOR SYMPTOMATIC CONTROL

or corrosion; insulation might fail; the generator battery can be depleted prematurely; or the generator itself can fail (e.g., by supplying excessive or unacceptable stimulation). 195,196 Cost-effectiveness Although the initial expense of implanted SCS equipment creates a potential barrier to patient access, investigators have established that SCS is cost-effective in the treatment of FBSS, 197–200 CRPS, 201 PVD, and angina. 156,202 Cost recovery oc­ curs in approximately 3 years in patients with FBSS or CRPS, after 1 year in patients with angina who are not candidates for coronary artery bypass surgery, and immediately in patients with angina who would otherwise receive coronary artery by­ pass surgery only for symptom relief. The cost-effectiveness of SCS will be improved by the devel­ opment of new equipment and techniques and can be enhanced by minimizing the incidence of complications (especially those, such as infection, that require surgical intervention and system replacement) and by careful patient selection. The incidence of complications can be reduced if the spe­ cialist is meticulous, technically proficient, and knowledgeable (e.g., a simple technique nearly eliminates percutaneous elec­ trode migration). 187 One improvement that has had a direct impact on cost-effectiveness is the development of equipment designed to facilitate noninvasive reprogramming to optimize pain/paresthesia overlap. Another improvement, the introduc­ tion of rechargeable batteries, is intended to extend the life of expensive implanted pulse generators. 203 Spinal Cord Stimulation Challenges In common with most medical therapies, we can improve pa­ tient outcomes with SCS by improving patient selection crite­ ria, equipment design, implantation techniques, and clinician training. Continued investigation of the mechanisms of action of SCS will allow us to potentiate the benefits of the therapy, and developing refined outcome measures and appropriate re­ search techniques will help us to optimize clinical application. The increasing presence of magnetic fields in our environ­ ment and in the use of higher field strengths in MRI investi­ gations motivates the development of electrodes and pulse generators that will tolerate the magnetic fields. SCS remains an underused therapy that should be considered early in the treatment continuum for a large group of patients. References 1. Largus S. Compositiones . Helmreich G, ed. Leipzig: Tuebner; 1887. 2. Shealy CN, Mortimer JT, Reswick JB. Electrical inhibition of pain by stim­ ulation of the dorsal columns: preliminary clinical report. Anesth Analg 1967;46(4):489–491. 3. Melzack P, Wall PD. Pain mechanisms: a new theory. Science 1965;150(3699): 971–978. 4. Lindblom U, Meyerson BA. Influence on touch, vibration and cutaneous pain of dorsal column stimulation in man. Pain 1975;1:257–270. 5. Linderoth B, Meyerson BA. Dorsal column stimulation: modulation of so­ matosensory and autonomic function. In: McMahon SB, Wall PD, eds. The Neurobiology of Pain. Seminars in the Neurosciences . London: Academic Press; 1995:263–277. 6. Campbell JN, Davis KD, Meyer RA, et al. The mechanism by which spi­ nal cord stimulation affects pain: evidence for a new hypothesis. Pain 1990;5:S228. 7. Dickenson AH. Gate control theory of pain stands the test of time. Br J Anaesth 2002;88(6):755–757. 8. Nashold B, Somjen G, Friedman H. Paresthesias and EEG potentials evoked by stimulation of the dorsal funiculi in man. Exp Neurol 1972;36(2): 273–287. 9. Hosobuchi Y, Adams JE, Weinstein PR. Preliminary percutaneous dorsal column stimulation prior to permanent implantation. J Neurosurg 1972; 37(2):242–245. 10. Law JD. Spinal stimulation: statistical superiority of monophasic stimula­ tion of narrowly separated bipoles having rostral cathodes. Appl Neuro- physiol 1983;46:129–137.

Spinal Cord Stimulation Treatment Challenges CLINICAL FAILURE

The loss of pain relief despite pain/paresthesia overlap in a func­ tioning system occurs in a minority of patients. This clinical failure might have a neurochemical basis, and it might respond to adjuvant medical therapy with baclofen or gabapentin. Clin­ ical failure can also occur if the patient develops (1) pain in a new location that cannot be covered by paresthesia unless the equipment is revised surgically, (2) troublesome postural changes in paresthesia coverage, or (3) excessive pain/irritation at the implant site that is not caused by infection and cannot be treated locally. BIOLOGIC FAILURE Infection, the most common biologic failure, is almost always treated successfully (treatment, however, is expensive because it generally requires removal and replacement of the SCS system). The risk of infection is small, however, and is reduced by main­ taining sterility and administering prophylactic intravenous an­ tibiotics. Should an infection occur, specimen culture will guide antibiotic therapy. Unless the infection is limited to the skin over the implant, the entire SCS system should be removed until the infection resolves, when a new system can be implanted. Clinicians have reported patients with an “allergic reaction” to the implant, but this is rare and might be undiagnosed in­ fection. A second biologic failure, the development of fibrosis around implanted electrodes, can impede treatment, but this problem generally can be overcome through reprogramming. PSYCHOLOGICAL FAILURE Psychological problems, such as conversion disorder, 193 can re­ quire system removal. TECHNICAL FAILURE Technical failure, the inability to achieve or loss of clinically useful pain/paresthesia overlap, can result from suboptimal electrode choice or placement, from electrode migration, or from equipment malfunction. Technical failure can be mit­ igated by increasing clinician skill and experience, which includes adoption of the best implantation techniques; for example, the risk of percutaneous electrode migration can be nearly eliminated by applying an adhesive to the anchor/strain relief during implantation, 187,194 and the risk of fatigue fracture can be lessened by implanting the pulse generator in the lateral abdomen instead of the buttock and by creating strain relief coils in appropriate places. In patients with suspected spinal stenosis or another ana­ tomic anomaly that increases the risk of spinal cord or nerve injury, it is prudent to obtain an MRI of the target spinal areas before implantation of a surgical plate/paddle electrode. With the SCS system in place, computed tomography myelography is an alternative. The risk of dural puncture is reduced by using an anesthetic technique that permits patient feedback during implantation of an electrode and avoiding placement in scarred areas, and the risk of epidural hematoma is reduced by preoperative review of the patient’s coagulation history, medications, and blood chem­ istry and by monitoring the patient for a reasonable amount of time. Uncomfortable extraneous paresthesia or motor re­ sponses can be avoided by careful electrode implantation and postoperative adjustment or by use of an insulated surgical plate/paddle electrode. EQUIPMENT FAILURE Every part of an SCS system can fail. The electrode/lead/extension conductors can develop an open circuit through fatigue, fracture,