The effects of spinal cord stimulation on nerve function in low back pain

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Spinal cord stimulation (SCS) has been employed for the management of chronic pain for over 50 years. Over this time SCS has become a well-established mode of treatment for neuropathic pain. Until recently most success with SCS has been obtained with pain involving the limbs (e.g. CRPS, sciatica, ischaemic limb pain and peripheral neuropathy). Relief of axial back pain has been more difficult to achieve. In response to problems associated with SCS (stimulation variance with body position, MRI lead incompatibility, difficulties covering certain pain sites) a wide range of device options have developed. As a result the number of companies manufacturing implantable spinal cord stimulators continues to increase with each company claiming specific benefits for their device range. The most dramatic recent change has been the introduction of high frequency (HF) SCS (500 Hz to 10,000 Hz). Early work on HF SCS demonstrated potential benefits on axial back pain. The additional feature of “paraesthesia-free” stimulation to avoid the need for paraesthesias required by the more conventional tonic low frequency (LF) SCS (<100Hz) has made this form of stimulation more attractive. Paraesthesias have the potential for discomfort particularly with changes in position (standing to lying). In 2015, a landmark prospective randomised trial was published (Kapural et al) reporting superiority of HF SCS over LF SCS for axial back pain. While the mechanisms of action for conventional SCS are still being investigated, even less is known about HF stimulation. Given the positive results reported by Kapural et al it is likely that the use of HF SCS will dramatically increase. While no definitive evidence of neural damage has been found on clinical examination concern has been raised in animal studies about the potential for long-term neural changes with HF SCS. In addition certain patient subpopulations may be more vulnerable to stimulation induced changes in neural function particularly those with spinal canal stenosis (personal communication). Given Kapural et al has only recently been published consensus regarding the long-term use of HF SCS in axial low back pain is yet to be reached. This pilot study will monitor changes in neural function associated with propriety LF (<100Hz) and HF (10kHz) SCS implantation in people with chronic low back pain over twelve months. The project will inform the development of a full-scale trial. The Global Burden of Disease study now ranks low back pain (LBP) as the number one cause of disability in Australasia. Three million Australians now have long-term disability due to chronic LBP, costing more than $14 billion each year. As a result of a recent successful high profile multi-centre trial HF SCS implantation for chronic LBP is likely to increase. It is crucial therefore to obtain long-term safety data on this treatment to better inform patient selection and future cost benefit analyses.

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