Neurostimulation techniques have been used in the management of pain for close to 50 years. Transcutaneous electrical nerve stimulation (TENS) represents one of the most widely utilized external neuromodulation devices. Over the past several decades, more complex forms of neurostimulation devices and techniques have been developed and implemented in pain management practice for permanent human implantation. These include peripheral nerve stimulation (PNS), peripheral nerve field stimulation (PNFS), spinal cord stimulation (SCS), and intracranial stimulation (ICS). More patients suffering from intractable pain elect to undergo neurostimulation device implantation after failure of conservative management techniques for pain control. The advantages from a patient's perspective include an essentially side-effect free device under direct patient control that can be dynamically self-adjusted to his or her level of pain and activity.
For physicians, electrical implantable therapies have gained popularity because of safety, long-term efficacy, and cost savings.
The inspiration for development of these technologies came from the landmark “gate control theory” introduced by Melzack and Wall in 1965.1 Although this model fails to explain certain phenomena seen in painful conditions and cannot account for all of the observed effects of neurostimulation, the gate control theory remains the primary paradigm used to describe how neurostimulation acts to modify pain transmission. The gate control theory is based on the presence of interneurons in the dorsal horn of the spinal cord that receive afferent signals from peripheral C fibers (which convey painful stimuli) as well as nonnociceptive sensory fibers. When pain signals reach these dorsal horn interneurons, a “gate” is activated, allowing painful impulses to propagate along ascending fibers to the brain and resulting in conscious awareness of pain. Wall and Melzack proposed that the “gate” could be closed to transmission of painful impulses by means of selective activation of nonnociceptive sensory fibers. With this hypothesis, the notion of using neurostimulatory devices to preferentially activate nonnociceptive sensory fibers as a means of diminishing pain was born.
The application of neurostimulation has expanded dramatically since C. Norman Shealy implanted the first spinal cord stimulator in 1967. Current indications for the use of these devices (worldwide) include failed back surgery syndrome (FBSS), complex regional pain syndrome (CRPS), peripheral vascular disease (PVD) with critical limb ischemia, refractory angina pectoris, deafferentation syndromes, isolated peripheral nerve injuries, spinal cord injury related pain, interstitial cystitis, and trigeminal neuralgia. The range of painful conditions amenable to treatment with these techniques continues to broaden with more recent studies suggesting the potential for these devices to provide relief of chronic visceral pain, headaches, and poststroke pain. In addition to treatment of pain, neurostimulation may also be useful as a means to monitor evoked potentials during thoracoabdominal aneurysm repair2 and in the treatment of movement disorders (dystonia, Parkinson disease, and essential tremor), Tourette syndrome, major depression, and obsessive-compulsive disorder.
TAXONOMY, ANATOMIC TARGETS, APPLICATIONS AND MECHANISMS OF ACTION