Over the years many of our clients have undergone spinal cord stimulation (SCS) and it’s now a little over 7 years since we published the first of several articles on this subject. At that time, although the technology had been available for around 40 years, SCS remained a relatively novel procedure, certainly in the UK. There was usually little or no choice of model – you accepted what was on offer – and those that were offered were, generally speaking, less effective than those available today.
Subsequently, two SCS veterans, Libby and Peter, who each suffer Complex Regional Pain Syndrome in a lower limb, have written to share their experiences. Interestingly, Peter’s stim is a ‘newer’ high frequency model, the Nevro Senza HF10.
A current client of ours, Paul, who underwent his original SCS implantation some time ago, has recently had his low frequency stim removed and a high frequency replacement has been recommended (see below).
High or low frequency?
So what exactly is the difference between high and low frequency stims?
Traditionally, stims have delivered their electrical impulses at low frequencies, commonly 40 to 60 Hertz, for between 300 and 600 microseconds each. This results in paraesthesia, a sensation of tingling, numbness, or sometimes even burning. The purpose of the paraesthesia is to mask the pain. The effectiveness of low frequency stims depends upon the accuracy of the overlap between pain and paraesthesia, the idea being that paraesthesia is easier to endure than pain.
On the other hand, high frequency stims, such as Peter’s HF10, deliver impulses at a much higher frequency, usually around 10,000 Hertz, and the impulses are substantially shorter, typically around 30 microseconds. In most cases this results in the delivery of pain relief with no corresponding paraesthesia.
Which is most effective for pain relief?
In terms of levels of pain relief, this is always subjective and, as is to be expected, figures vary from study to study. Taking a common example of low back pain, some studies report that the percentage effectiveness of pain relief is as much as 30% greater for high frequency stims – a stark difference. It should be stressed, however, that other studies have found little or no difference between the two.
In a study reported in November 2016, 171 people suffering back and leg pain were randomly implanted with either a high frequency (HF10) or low frequency stim. At two years post-implantation, on average, significantly more people were still experiencing pain relief with the high frequency stim (76.5% vs 49.3% for back pain and 72.9% vs 49.3% for leg pain). Further, for both back and leg pain the level of pain relief was on average significantly greater with the high frequency stim (66.9% vs 41.1% for back pain and 65.1% vs 46% for leg pain).
The report’s authors, a number of whom, it should be noted, declared current or past financial interests with stim manufacturers, concluded that:
“The advantages of HF10 therapy are anticipated to impact the management of patients with chronic back and leg pain substantially, and possibly other pain conditions. The superior and durable results demonstrated in this study are anticipated to lead to improved long-term cost effectiveness and payer acceptance, making this therapy broadly available to patients suffering from chronic pain.”
In the case of our client, Paul, who suffers CRPS in his left foot and ankle, following the original procedure he estimated that his low frequency stim was providing around 30% pain relief, but as time went by this reduced to the point where any benefit was, at best, negligible. His pain consultant feels confident that there is “a very reasonable prospect of him achieving a good degree of pain relief” with a high frequency stim, although for other health reasons it is not immediately possible for him to undergo the second procedure.
Of course, even if the popularity of low frequency stims begins to wane, there remain other options to consider:
- There are now MRI-friendly stims. A client of ours with a history of recurrent spinal surgery has opted recently for an MRI-friendly stim given the very high prospect of her requiring further spinal imaging in the future.
- The ongoing debate as to Spinal Cord Stimulation vs Dorsal Root Ganglion (DRG) Stimulation. Are the days of SCS numbered in any event?
- Do implanted pain pumps still have a role to play?