Neurophysiological evidence of antidromic activation of large myelinated fibres in lower limbs during spinal cord stimulation

Study Design. This study was designed to verify the hypothesis of a constant, antidromic activation of fibers traveling along peripheral sensory nerves during spinal cord stimulation (SCS). Objective. To investigate the neurophysiological characteristics (latency, amplitude, waveform) of potentials recorded in peripheral sensory nerves during the SCS. Summary of Background Data. SCS is widely used for the relief of chronic benign pain resistant to conservative therapies, but its antalgic mechanism is poorly understood. Antidromic activation of peripheral nerve fibers is one of the hypothesized antalgic mechanisms, but very few neurophysiological studies have been conducted on this subject. Methods. Sixteen patients undergoing a percutaneous test trial of SCS for chronic pain in the lower limb (4 males, 12 females, mean age of 54.2, and age range 41-77 years) were enrolled. Diagnoses included: failed back surgery syndrome, complex regional pain syndrome type I, painful lumbosacral radiculopathy, and painful peripheral neuropathy. All patients had a lead percutaneously implanted in the epidural space at a vertebral level ranging from T9-T12. Nerve action potentials were generally recorded in nonpainful leg but, when the pain was outside the investigated nerve territory, a bilateral recording was performed. Twenty-one different studies were carried out on 16 patients. Results. The results confirmed the hypothesis that cutaneous afferents were regularly activated by SCS. Conclusion. The authors hypothesize that this antidromic activation could represent a possible antalgic mechanism of SCS in patients with peripheral neuropathic pain, but further neurophysiological studies will be needed to elucidate this hypothesis.