Spinal cord stimulation (SCS) is a successful treatment in patients with intractable
neuropathic pain. This therapy is most commonly used in patients who have chronic
neuropathic pain following failed surgery, known as failed back surgery syndrome (FBSS) .
There is evidence from previous studies to demonstrate that SCS can provide a 50- 70%
reduction in pain medication and pain scores. A randomised controlled study compared SCS
with conventional medical management (CMM). When compared with the CMM group; the SCS
patients had a 50% pain reduction in their back pain and leg pain. The results suggested
that patients who received SCS had better pain relief and health related quality of life
over a period of 6 to 12 months compared to the CMM group. Additionally, these patients
reported satisfaction in SCS treatment, continuous pain relief, and clinical improvements
in functional capacity and health-related quality of life.
On the other hand, SCS has been progressively being used in patients with intractable
neuropathic pain who have not undergone spinal back surgery ("Virgin-back''). The UK NICE
guidelines have recommended SCS as a treatment option for patients with intractable
neuropathic spinal pain, including patients who have not undergone previous spinal
surgery (NICE, 2008).
One of the main drawbacks of conventional SCS is the onset of parathesia, despite being
an effective therapy for neuropathic pain. This can cause abnormal sensations or
considerable discomfort to the patient during activity or sudden position changes.
Typically, conventional SCS operate at frequencies ranging from 40-80 Hz, long pulse
widths of 300-500 µsec, and amplitudes to stimulate patient's pain sensory percept
distribution. These frequencies are often used because sensory perception is often lost
at 300 Hz. Current studies have found that delivering stimulating frequencies below the
upper limit of what may cause parathesia; may reduce discomfort and abnormal sensations,
increasing the tolerability of SCS treatment. Parathesia is considered necessary in order
to cover the painful area and provide maximum pain relief. However recent research
suggests that parathesia may not be necessary for pain relief, and in fact that pain
awareness can provide full benefits of SCS.
Data from (PROCO RCT) indicates that similar pain relief and improvement in quality of
life measures are experienced independent of the type of frequency (from 1kHz up to
10kHz) used in paraesthesia free SCS therapy when the proper target and dose are
identified. Further, the study showed that 1kHz stimulation provides similar pain relief
using significantly less energy than higher frequencies.
High frequency (HF) stimulation is a new promising, new stimulation paradigm involving
higher frequency, lower pulse widths, and lower amplitudes when compared to conventional
SCS. The effectiveness of HF-SCS is controlled by the amount of Neural dose (frequency,
amplitude and pulse width) passing the electrodes and reaching the neural tissue,
resulting in minimal discomfort and damage to the tissues before the definite shape of
the impulse.
Pre-clinical Data
A study testing the efficacy of kilohertz and conventional SCS was done on rat models
during different pain conditions. The findings established that higher frequencies can be
delivered at lower amplitudes whilst reversing pain behaviours as seen at 50 Hz and at
higher intensity of motor threshold.
Moreover, both conventional and kilohertz frequency SCS forms intensity and
frequency-dependant inhibition of mechanical hypersensitivity, in animal models of
neuropathic pain. Different intensities (20, 40 and 80% motor threshold) and frequencies
(50, 1kHz and 10kHz) were used. At each frequency, the pulse width was constant. It was
observed that as frequency was increased, the pulse density also increased.
Clinical data
Previous randomised control trials have provided evidence that using frequency ≤1200 Hz
and pulses ≤ 5% provides efficient relief with HF- SCS.
A multi-centre trial previously conducted to see the effects of HF-SCS on patients being
delivered up to 10 kHz of stimulation. Patients were assessed for pain ratings,
disability, sleep disturbances, and satisfaction, as well as complication rates for up to
six months. When results were compared to baseline, 88% of patients reported a
significant reduction in mean back visual analogue scores (VAS) from 8.4 to 2.7 at six
months. Seventy four per cent of patients reported more than 50% back pain relief at six
months. Overall it was concluded that individuals in the trial group with chronic back
pain, 70% of patients were provided with positive improvement and experienced sustained
low back and leg pain relief. Substantial improvements were also seen for these patients
with disability and sleep disturbances.
If clinically considered, the NRS has substantially reduced in patients who received
HF-SCS than conventional SCS in patients with neuropathic pain and FBSS. This suggests
that HF may provide relief in virgin-back patients. Since there remains limited research
in this area therefore, the main objective of our study is to investigate the response to
1000Hz frequency following SCS treatment in "virgin back" patients with intractable lower
limb neuropathic pain. However based on the PROCO RCT and further WHISPER trial, we aim
to establish role of microburst and combination therapy in non-responders.
Our sample size of 30 patients will allow detection of minimal important difference of
2.0 on the NRS pain scale at 90% power and alpha of 5%, assuming an outcome standard
deviation of 2.5 and attrition rate at 12-months of 30%. Patient primary and secondary
outcomes at each follow up point will be compared to baseline values. Data analyses will
take account of the paired nature of the data and use non-independent t-test for
continuous outcomes and McNemar's test for binary outcomes.
The primary objective is to investigate the clinical response to high frequency
(1,000Hz) in patients who are due to have percutaneous spinal cord stimulation for
intractable lower limb neuropathic pain
The secondary objective will be to investigate the effect on functionality and
quality of life and adverse events at the high frequency group (1000Hz)