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Many conditions can be treated with neuromodulation but the most widely used application is the treatment of chronic pain with spinal cord stimulation. 4 Several clini- cal studies have supported the effectiveness of SCS in treating chronic pain due to failed back surgery syndrome (FBSS), complex regional pain syndrome (CRPS), diabetic peripheral neuropathy, postherpetic neuralgia and periph- eral vascular disease. 5 The spinal cord stimulator was first used in 1967 but didn’t gain FDA approval until 1989. 5 Before the advent of commercially available peripheral nerve stimulators, the spinal cord stimulator was the only neuromodulation treatment option for patients suffering from peripheral neuropathies and CRPS. Advancements in the development of peripheral nerve stimulation over the last decade has precluded the use of spinal cord stimulators for peripheral nerve pain. The FDA approval of the dorsal root ganglion stimulator (DRGS) in 2016 6 and the Peripheral Nerve Stimulator in 2015 7 changed the neuromodulation landscape with the offering of more targeted and specific neurostimulators. There are clear advantages in selecting a peripheral nerve stimulator over a spinal cord stimulator when neuromod- ulating a peripheral nerve. A spinal cord stimulator lead electrode measures two to three times longer than a PNS lead; and while SCS leads work well for implantation in the spinal column, they have drawbacks when employed for peripheral nerve stimulation in the extremities. Spi- nal cord stimulator leads have a higher tendency for lead migration and impedance when used in the periphery compared to PNS leads which are smaller and anatomi- cally well-suited for peripheral nerves. 8 HISTORY OF PNS Although PNS has only recently been introduced as an accepted treatment for chronic pain in the United States, the use of electricity to treat peripheral nerve pain can be traced to the Roman Empire. In 15 AD Scribonius, physician to the Roman Emperor Tiberius, observed that a patient who accidentally stepped on an electric torpedo fish had less gout pain afterwards. 9 This led Scribonius to recommend the use of torpedo fish for chronic pain. 9 Despite this early yet anec- dotal discovery, advances in PNS didn’t significantly prog- ress until the 1960’s. In 1965, doctors Wall and Sweet docu- mented the first PNS surgery. They implanted an electrode on the median and ulnar nerves of a 26-year-old woman with a history of pain and neuropathy in the fingers and hand. 1 When the nerves were stimulated, pain diminished and was replaced with a tingling feeling known as paresthe- sia. 1 Development of PNS continued over the next fifty years from an open procedure that was prone to complications to one that is minimally invasive and relatively safe. 10 ANATOMY AND PHYSIOLOGY OF PAIN TRANSMISSION A brief review of the relevant anatomy involved in pain transmission aids in understanding how neuromodulation works. Nociceptors also known as pain receptors respond to mechanical, thermal or chemical stimuli. In the skin there are A-beta, A-delta and C nociceptors whose axons terminate in the dorsal horn of the spinal column. 11 The A-beta nerve fibers respond to touch, are larger than A-delta and C fibers and have a relatively fast conduction speed. 12 Pain transmission and modulation is accomplished by ascending and descending pathways in the spinal cord. When pain signals reach the dorsal horn from the periphery, they are transmitted by interneurons to the spinothalamic tract, the ascending pathway in the spinal cord. The signals travel up the spinothalamic tract, through the medulla and to the thalamus. From the thalamus the pain signals are relayed to the somatosensory cortex. Sensory information reaches the midbrain where the descending pathway originates. The descending pathway aids in modulating pain transmis- sion through the release of neurotransmitters in the dorsal horn. 13 An individual’s perception of pain is the result of the interplay between the pathways. GATE CONTROL THEORY The field of neuromodulation gained traction with the pub- lication of Melzack and Wall’s Gate Control Theory in 1965. This theory proposed that the transmission of pain signals in the dorsal horn depends on the type of peripheral nerve fiber stimulated. 14 Small A-delta and C peripheral nerve fibers inhibit cells in the area of the dorsal horn that inhibit transmission of sensory input to the somatosensory cor- Peripheral nerve stimulation (PNS) is a type of neuromodulation emerging as an effective non-narcotic treat- ment option for chronic neuropath- ic pain. | The Surgical Technologist | SEPTEMBER 2020 404