Concepts and Innovations

Copyright © 2010 by the Congress of Neurological Surgeons The management of chronic, intractable neuropathic pain by electrical spinal cord stimulation (SCS) is a well-established clinical method.1 The method is based on the gate-control theory of Melzack and Wall,2 who postulated that activity in large-diameter cutaneous fibers (Aβ fibers) inhibits the transmission of noxious information to the brain. Electrical stimulation of these large afferents by an electrode placed dorsomedially in the epidural space elicits a tingling sensation (paresthesia) in the corresponding dermatomes. To obtain successful treatment of chronic neuropathic pain by SCS, the stimulation-induced paresthesia must cover the pain area completely.3,4 In SCS, an electrode is positioned over the spinal cord and connected to an internal pulse generator. All pulse generators currently available deliver tonic pulses that can be modified by altering the pulse width, frequency, and amplitude to get maximal pain suppression. The internal pulse generators can use either constant voltage or constant current to modulate the underlying cells or networks. Some neurons in the central nervous system in cluding the spinal cord fire in groups of action potentials followed by periods of quiescence (bursts), whereas others, in the same stage of sensory processing, fire in a tonic continuous manner. Information theory suggests that both bursting and tonically firing model neurons efficiently transmit information about the stimulus. Burst and tonic firing might be parallel firing modes in certain sensory systems.5,6 Based on animal studies, it is suggested that burst firing is more powerful than tonic firing in activating the cerebral cortex.7-10 This may be Burst Spinal Cord Stimulation: Toward Paresthesia-Free Pain Suppression