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

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PART FIVE  METHODS FOR SYMPTOMATIC CONTROL

Some clinicians are using cervical SCS in exploratory trials to improve cerebral blood flow in patients recovering from stroke, 167 coma, 168 or brain tumors. 169 VISCERAL PAIN AND DYSFUNCTION SCS and other forms of neurostimulation are also being used to treat visceral dysfunction and pain associated with such dis­ eases as interstitial cystitis, 170 pancreatitis, 171 motility disorders, urinary urgency and frequency, 172 pelvic pain, 173 vulvodynia, 174 and pelvic floor dysfunction. 175 Potential Beneficial Outcomes TECHNICAL GOAL The technical goal of conventional SCS is to cover a patient’s pain with a comfortable level of paresthesia; this has been a necessary but not sufficient condition for therapeutic success. Recent paresthesia free waveforms and settings have contin­ ued to use paresthesia mapping data, whether historical or in­ dividualized, to optimize electrode placement. If an electrode migrates or if pain changes location, appropriate paresthesia coverage can be lost. Thus, contemporary SCS systems are designed to allow adjustment of stimulation parameters post­ implant to steer paresthesia to a new location or to recapture coverage. Only occasionally does readjustment for these pur­ poses require a surgical intervention. It is possible for paresthesia to cover the painful area with­ out providing an analgesic effect. Such clinical failure can become evident during the screening trial or can arise after a period of success. On rare occasions, a patient who experiences technical success and pain relief dislikes the sensation of pares­ thesia and decides not to continue the therapy. New waveforms offer additional options for these patients. CLINICAL GOALS A commonly used definition of “success” in treatment for pain is a minimum of 50% pain relief, but this and other measures all have limitations. 176 Additional reported benefits of SCS in­ clude (1) reduced consumption of medication and other health care resources; (2) improved ability to engage in the activities of daily living, quality of life, neurologic function, and symp­ toms of emotional depression; and (3) return to work when uncontrolled chronic pain was the only impediment (and gen­ erally when the patient has been out of work for less than 2 years). 177,178 In patients suffering from ischemic pain, SCS can improve microcirculation and tissue oxygenation. This, in turn, can pro­ mote the healing of ischemic ulcers and increase the possibility of limb salvage. Prognostic Factors Demographics are of little help in choosing the ideal SCS can­ didate. Age is only a factor in children, where the safety and effectiveness of SCS is not established, and in the elderly, who might have difficulty dealing with the patient interface (or recharging a battery), but, as for example with driving cars, the effect of advanced age must be assessed on an individual basis. Researchers have reported some outcome differences be­ tween men and women, but these have been minor and of little if any practical value. Thus, the only sex-related caveat is that the safety of SCS during pregnancy is not established (although pregnant women have continued to use SCS rather than suffer known and suspected adverse effects of alternative pain treat­ ments). Even a very short life expectancy does not rule out SCS, which can be cost-effective for short-term use if an external stimulator is used.

Indications NEUROPATHIC PAIN

In the United States, the major indication for SCS is the treat­ ment of FBSS, particularly with a component of neuropathic pain. Two randomized controlled trials (RCTs) have demon­ strated the superiority of treating FBSS with SCS versus reop­ eration 141 or optimized conventional medical management. 142 Of course, an FBSS patient with gross instability or a neuro­ logic deficit caused by neural compression that is evident on an imaging study would undergo a corrective surgical procedure before or instead of SCS. It is easier to achieve pain relief in the limbs than in the low back because low back pain is more likely than leg pain to have a nociceptive component, which is not expected to respond to SCS with conventional waveforms; also, pain/paresthesia over­ lap in the low back is generally more difficult to achieve, even with complex electrode arrays and detailed psychophysical tests. At one time, achieving low back pain relief with SCS was considered rare; however, Law’s 143 research on techniques to guide paresthesia coverage kept the low back available as an SCS therapeutic target, and clinicians have built on his work to define the best electrodes 144 and contact combinations 86 for achieving pain relief in the low back. Over the past 5 years, 10-kHz stimulation has been reported to be highly effective for FBSS and in one head-to-head RCT comparison to be superior to conventional SCS. 145–148 The most recent such comparisons, however, have shown conventional and high frequencies to be equally effective. 146,149 “Burst” SCS also has been reported to be highly effective for FBSS, 69,70,150 and most recently, an RCT comparing burst with conventional waveforms showed burst to be superior, but in crossover com­ parisons, a substantial fraction (20%) of patients preferred the conventional waveform, showing the clinical importance of a device which delivers multiple waveforms. 151 The use of SCS to treat pain in the limbs arising from com­ plex regional pain syndrome type I (CRPS I) (reflex sympathetic dystrophy) is also supported by data from an RCT. 152,153 In that study, 5 years posttreatment, the 20 patients remaining in the group that actually received SCS reported better pain relief and superior global perceived effect than did those patients remain­ ing in the alternate group who did not receive SCS. 154 More recently, HF and burst SCS also have been reported to be effec­ tive for CRPS, with individual patients showing preferences for one or the other, or for conventional waveforms. 84 Other neuropathic pain indications for SCS include phan­ tom limb/postamputation syndrome, postherpetic neuralgia, root injury pain, and pain/spasm arising from spinal cord in­ jury or lesion. ISCHEMIC PAIN In Europe, clinicians have gathered evidence on the efficacy of SCS in the treatment of ischemic pain caused by refractory angina (including syndrome X), 155–158 PVD, 159,160 Raynaud’s syndrome, and diabetic neuropathy. As noted earlier, in pa­ tients with ischemia, SCS not only treats the pain but also has a positive effect on the underlying ischemia. Thus, the outcome criteria used to document the impact of SCS on critical limb ischemia arising from PVD include survival, limb salvage, and measures of microcirculation 161 as well as pain relief. In Raynaud’s syndrome, the few published studies (all of which involve small numbers of patients) demonstrate the pos­ itive effect of SCS therapy. 162–166 This is not surprising because, compared with PVD patients, patients with vasospastic condi­ tions are relatively young, present with relatively few obliter­ ative vessel wall processes, and have symptoms that are often temporarily relieved by destroying or blocking the correspond­ ing sympathetic ganglia.