This study aims to investigate the clinical response to Spinal Cord Stimulation frequency parameters: 40Hz, 4000Hz and 10000Hz and explore the brain imaging changes using PET-CT scans. The response to these stimulator settings on health related quality of life will also be measured using validated questionnaires.

Spinal cord stimulation (SCS) is a treatment option for people suffering with chronic neuropathic back and leg pain. Conventionally, patients receiving SCS are provided with tonic stimulation parameters, where the frequency of electrical pulses is set at 40-60Hz. The major side effect of tonic SCS parameters is the onset of paraesthesia, a tingling or pins and needles sensation within the target region, which can cause discomfort for some patients. However, newer methods include high-frequency stimulation (HF) which is able to provide paraesthesia free stimulation, ultimately providing better patient tolerability. HF stimulation is widely offered to patients with SCS as part of routine clinical practice. However, the effect on pathways in the brain remains to be characterised. This study therefore aims to investigate the clinical response to three frequency parameters 40Hz, 4000Hz and 10000Hz and also explore the brain imaging changes using PET-CT scans. The response to these stimulator settings on health related quality of life will also be measured using validated questionnaires.

20 patients who are deemed suitable for SCS as part of NICE guidelines 159 pathway will be recruited for the study. All patients will have a baseline PET-CT scan and undergo first stage of SCS where they will be offered tonic 40Hz settings as part of trial stimulation. If successful (>50% improvement in pain scores) patients will be offered second stage and continue to receive 40Hz stimulation for 4 weeks. After a second PET-CT scan they are randomised to receive either 4000Hz or 10000Hz stimulation for 4 more weeks, then cross-over treatment for another 4 weeks. PET-CT scans will be performed between each level of stimulation and at the end of the study (4 in total).

Inclusion Criteria:

• Patients with intractable lumbar neuropathic pain who are due to receive Percutaneous Spinal Cord Stimulation as part of their standard treatment per NICE HTA guidance 159 at Barts Health NHS Hospitals.
• Patients between 18 and 75 years of age.
• Patients who have given their written informed consent.
• Female patients of childbearing potential must be using adequate contraception (i.e. using oral or IM contraception or an IUCD) and must have a negative urine pregnancy test.
• Patients must be able to communicate in English in order to complete validated questionnaires written in English only.

Exclusion Criteria:

• Patients with diabetes or any underlying neurological condition.
• Patients known to have a condition that in the investigator's judgement precludes participation in the study.
• Patients who have received an investigational drug or have used an investigational device in the 30 days preceding study entry.
• Patients unable to comply with the study assessments and to complete the questionnaires.