CHAPTER 17: Psychological Evaluation of Patients for Spinal Cord Stimulator Implantation

INTRODUCTION

More than 45 years ago, Shealy and colleagues introduced the concept of spinal cord stimulation (SCS) as a means of electrically inhibiting pain that was consonant with Melzack and Wall's gate-control theory of pain.^1-3 SCS, or neuromodulation, is now a widely used technique that delivers pulsed electrical signals, principally to the dorsal column of the spinal cord, for indications that include failed back surgery syndrome, traumatic nerve injury, postherpetic neuralgia, complex regional pain syndrome, refractory angina pectoris, peripheral vascular disease, neuropathic pain, and visceral pain.^4,5 The technique is minimally invasive and reversible; electrodes can frequently be placed percutaneously under local anesthesia during outpatient surgery; and, unlike more invasive surgical approaches, it does not ablate pain pathways or alter anatomy.^6,7 Although the exact mechanism of action is variously described, it is generally held that pain reduction is achieved by inhibiting the conduction of primary neural pathways through the stimulation of large nerve fibers that override the transmission of smaller nerve fibers more directly involved in pain sensation.^6,8-10

WHEN SPINAL CORD STIMULATION IS INDICATED

When indicated, SCS is generally a safe means of ameliorating chronic and otherwise poorly tractable pain and, when successful, can reduce patients’ dependence on medication—including opioid medication—while returning a fair degree of mobility and quality of life. It is no wonder, then, that the technique has proliferated in recent years to annual estimates in the 10,000 to 20,000 range worldwide for permanent implantation.^4,6,10,11 In general, a trial of SCS is considered successful if the patient reports at least a 50% reduction in pain in the affected area,¹² with initial success rates for achieving this threshold varying widely, from as low as 20% to as high as 80%, depending on the group studied, the particular pain syndrome targeted, the hospital or clinic reporting, and the patient selection criteria used.^4,13,14

Despite ongoing improvements in the technology of SCS and improved discrimination regarding the diagnoses most likely to respond favorably to the therapy, some studies suggest a significant loss of analgesia in 25% to 50% of patients within 12 to 24 months of implantation.^15-17 Although some of the variation can be attributed to operational factors—lead migration and erosion, electrical complications and malfunctions, and clinical misjudgment^10,18—an increasing amount of attention has been directed toward psychological variables, especially as these may be revealed and addressed through screening procedures during the patient selection process.^{4,6,8,10,11,14,19-22}

There is an ever-accumulating body of evidence that psychosocial variables are among the most predictive factors in the outcome of medical interventions and especially the outcome of invasive procedures, such as spinal surgeries.²³ Given the high variability ...