Sham-Controlled RCT on 10kHz High-Frequency Spinal Cord Stimulation for Chronic Neuropathic Low Back Pain (Modulate-LBP)

The prevalence of chronic low back pain in the population is estimated to range between at 12% and 28% (1-4). Within this group an estimated 12-15% of adults suffer from chronic neuropathic lower back pain (CNLBP), have relatively greater pain severity, and account for more of the costs of this condition (5,6). This subgroup of people with CNLBP are the focus of the proposed trial.

The National Institute for Health and Care Excellence (NICE) recommends SCS for refractory neuropathic pain (TA159) (7). It is routinely used for people with predominant, neuropathic, radicular pain typically resulting from, or persisting after, spinal surgery (so-called failed back surgery syndrome (FBSS) (8-10). SCS has been shown to be cost effective for this indication (11).

Conventional SCS consists of the insertion of a medical wire (lead) introduced into the epidural space through a needle puncture. The lead is then positioned to target the pain by passing current into the lead from an external power source to generate a pins and needles sensation (paraesthesias) over the painful area. Analgesia occurs when the paraesthesia overlaps and therefore masks the painful area. Once pain reduction is demonstrated, the battery is implanted under the skin of the abdomen, flank or buttock. SCS is most commonly used in the treatment of leg pain of FBSS. However, due to lack of existing evidence and the difficulty of obtaining paraesthesia over the low back, SCS has traditionally not been recommended for treating patients with back pain without previous back surgery (10, 12).

High frequency 10kHz-SCS is a recent major advance in SCS technology. The current is delivered at 10kHz frequency as opposed to the 40 to 60Hz generated by the conventional SCS (13). The key advantages of a higher frequency current are:

10kHz-SCS has been shown to be superior (14) to conventional SCS in targeting residual low back pain following back surgery. Moreover, it does not generate any stimulation related sensations or paraesthesia so is preferred by patients as they are saved from needing to experience these distracting and occasional shocking sensations of conventional SCS. Therefore, 10kHz-SCS allows to smoothly conduct sham controlled or double blind studies in the field of SCS without the need for device modifications.

The lead applicant conducted an uncontrolled, multicentre, single arm study with 83 people with significant low back pain with or without leg pain, implanted with a 10kHz-SCS. At 24 months, the mean reported VAS score for back pain was 3.3 (SD 0.3), compared with 8.4 (SD 0.1) at baseline (pre-implant) and 2.7 (SD 0.3) at 6 months with 60% of subjects reporting >50% back pain relief. Similar improvements were observed in leg pain, disability, sleep and marked reductions in medication intake (15).

In a more recent multicentre RCT, 10kHz-SCS therapy demonstrated superiority to conventional low-frequency SCS in the treatment of post-surgical neuropathic pain. A total of 198 subjects with both back and leg pain were randomised in a 1:1 ratio to a 10 KHz-SCS or conventional SCS. 10kHz-SCS decreased back pain intensity by 67% compared to 44% in the conventional SCS arm (16). This decrease was sustained at 24 months (17).

The above mentioned studies focused on neuropathic back pain in the context of patients with previous spinal surgery. However, a small subset of patients without prior spine surgery that received 10kHz-SCS therapy in both these studies have shown good pain relief and functional improvements in both studies comparable to those with FBSS (14,16).

The investigators hypothesised that patients with CNLBP with no prior spine surgery would benefit from 10kHz-SCS. To evaluate this hypothesis, the investigators initially designed and conducted an open label uncontrolled pilot study in 21 patients with CNLBP and no prior spine surgery. 10kHz-SCS therapy significantly reduced back pain intensity by an average of 5.59 (SD 1.80) (-72.6% vs baseline) at 12 months in medically refractory low back pain patients with no past history of spine surgery. 90% of the implanted patients were classified as responders (i.e. VAS back pain reduction >50%) at 12 months. The investigators also observed a significant increase in physical function scores and health-related quality of life at one year post 10kHz-SCS implant. Mean pain intensity was reduced by 73% and disability measured by the Oswestry Disability Index was reduced by 48%. Opioid medication intake decreased by 64% and mean EQ-5D quality of life scores improved from 0.16 to 0.47. More importantly 75% of patients were able to return to employment(18). This improvement was sustained at 3 years follow up (19).

Following these promising results, the investigators now intend to undertake a fully powered RCT to confirm our hypothesis that 10kHz-SCS is beneficial for CNLBP patients with no prior back surgery.

To date 10kHz-SCS has not been formally tested against a sham control condition in order to isolate the therapeutic effects from those induced by placebo. It is very possible that some of the benefit reported may be due to a placebo effect (enhanced by a surgical procedure) or reporting bias in either the patient or assessor. The investigators have therefore specifically designed this fully powered double blind randomised sham controlled trial of 10kHz-SCS to address this major methodological limitation of previous studies.