Progress in neurological surgery
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The effect of peripheral neurostimulation has traditionally been attributed to the activation of non-noxious afferent nerve fibers (Aβ-fibers) thought to modulate Aδ and C-fiber-mediated nociceptive transmission in the spinal cord, compatible with the 'gate control theory of pain'. The concept has been extended since its initial description and more recent experimental evidence suggests that the analgesic effects of peripheral nerve stimulation in pain states such as in chronic headache require an interplay of multiple influences. ⋯ Beyond the concept of neuromodulation--decreasing excitation or increasing inhibition--a prerequisite of this arrangement is the convergence of different types of afferent activity and an intact descending modulatory network. In this review, we focus on the functional anatomy, pathophysiological mechanisms and neurophysiological and pharmacological findings elucidating the central mechanisms of peripheral nerve stimulation.
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Recent research has highlighted the important role of the sphenopalatine ganglion (SPG) in cerebrovascular autonomic physiology and in the pathophysiology of cluster and migraine headaches as well as conditions of stroke and cerebral vasospasm. The relatively accessible location of the SPG within the pterygopalatine fossa and the development of options for minimally invasive approaches to the SPG make it an attractive target for neuromodulation approaches. The obvious advantage of SPG stimulation compared to ablative procedures on the SPG such as radiofrequency destruction and stereotactic radiosurgery is its reversibility and adjustable features. The on-going design of strategies for transient and continuous SPG stimulation on as needed basis using implantable SPG stimulators is an exciting new development which is expected to expand the clinical versatility of this technique.
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Peripheral subcutaneous stimulation has been utilized for a variety of painful conditions affecting the abdominal wall, including sequelae of hernia repair, painful surgical scars, ilio-inguinal neuritis. It has also occasionally been shown to be effective in patients with intractable abdominal visceral pain. Since this is a very recent modality, no large series or prospective studies exist. The results, however, are promising and certainly warrant further investigation.
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Occipital nerve stimulation may provide pain relief for patients with otherwise refractory primary headache disorders. While this treatment modality remains an off-label use of spinal cord stimulator technology, a growing body of literature documents surgical techniques, stimulation parameters, complications, and outcome of this novel form of neuromodulation. ⋯ A discussion of stimulation parameters used for occipital stimulation will be included. Prospective, blinded studies of occipital nerve stimulation may clarify the role of occipital stimulation in chronic headache management.
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Neuromodulation practitioners increasingly recognize the potential for peripheral nerve field stimulation (PNfS) to treat pain originating from the trunk. Conditions resulting in truncal pain that may respond to PNfS include cervical and lumbar postlaminectomy syndrome, inguinal neurapraxia, post-herpetic neuralgia, and post-thoracotomy pain. The focus of this chapter is to review the mechanism of action in PNfS, patient selection factors, programming strategies, and technical considerations.