Pain suppression in the language of nature

Stefan Schu

Stefan Schu writes about the evolution of burst spinal cord stimulation and how it has changed the face of spinal cord stimulation therapy for the better.

Today, around 280 million people worldwide suffer from chronic neuropathic pain which can result from injury or disease affecting the nervous system (brain, spinal cord or other nerves). This type of pain is notoriously difficult to treat with more than 20 million people being refractory to standard medical treatment. Spinal cord stimulation is a well-established therapy for the management of chronic neuropathic pain. A small battery-powered generator implanted under the skin delivers mild electrical pulses to the spinal cord via electrodes placed in the epidural space and connected to the generator by fine wires. The pain suppression effect of spinal cord stimulation is based upon the concept of overlapping the pain signals in the brain by electrical stimuli produced by the generator. The principle is analogous to the immediate pain suppression effect of cold applied after a burn injury. The therapy is safe, reversible, and offers a high rate of success in well-selected patients.

Up until recently, spinal cord stimulation systems were designed to suppress pain by the delivery of regular and consistent electrical pulses in a pattern called tonic stimulation. While most patients tolerate tonic stimulation very well, it does have several downsides. One such downside is that successful therapy is dependent upon stimulation eliciting a tingling feeling called paraesthesia, which must cover the whole area of pain. Even when the area of pain is small and localised, the area of paraesthesia tends to be large. For some patients, this tingling feeling can be uncomfortable at least some of the time. In our experience, patients usually prefer not to be reminded of their unpleasant pain condition by any sensation in the affected area and, in some cases, patients discontinue spinal cord stimulation therapy as a result of the paraesthesia. Another downside relates to the proportion of patients who do not respond to tonic stimulation, or whose response diminishes over time. What options are left for these patients?

The neurons in our body transmit pain signals via tonic pulses or packets of high-frequency pulses, so called bursts. Recently, cutting-edge research has led to the development of a new stimulation paradigm called “burst stimulation” mimicking the language of nature. Burst stimulation (Prodigy, St Jude Medical) consists of a set of several high-frequency pulses that are delivered periodically to the area of pain. Clinical studies in the field report very interesting findings. They show that burst stimulation results in better pain suppression than tonic stimulation with no (or very little) paraesthesia felt by the patients. In particular, burst stimulation is associated with a significant decrease in pain vigilance and awareness compared with tonic stimulation. One study reported that nearly two-thirds of patients who did not respond to tonic stimulation achieved good pain control with burst stimulation. Pain suppression also improved for most people who already responded to tonic stimulation and then switched to burst stimulation.

The difference in pain outcomes between burst and tonic stimulation is thought to relate to the ways in which they engage the different pain pathways in the brain. The lateral pain pathway mediates how we experience the intensity, location and duration of pain while the medial pain pathway controls our emotional response to pain and how much attention we pay to it. Functional MRI has shown that tonic stimulation mainly activates the lateral pain pathway. The finding that burst stimulation can significantly decrease pain vigilance and awareness has led researchers to hypothesise that burst stimulation modulates both the medial and lateral pain pathways. This concept also fits with other research results indicating that neurons firing in a tonic pattern trigger the lateral pain pathway while neurons firing in a burst pattern trigger the medial pain pathway.

Burst stimulation appears to have a much wider potential to address awareness and feelings about pain by tuning into the body’s natural neural burst patterns. The absence of paraesthesia is also a benefit and may help some patients continue with spinal cord stimulation therapy for longer. In our clinical study, we found that 80% of patients preferred burst stimulation.

Burst stimulation represents an exciting new frontier in interventional pain management. Not only do we now have a stimulation paradigm that can deliver better pain suppression, we also have a much-needed new treatment possibility for patients with very few other options. The potential to affect a patient’s awareness and how they feel about pain is a tremendous step forward in pain therapy. It is an added silver lining that paraesthesia during spinal cord stimulation will become a thing of the past.

Stefan Schu is at the Department of Functional Neurosurgery and Stereotaxy, Neurosurgical Clinic, Heinrich Heine University, Dusseldorf, Germany