Electrophysiological Assessment of Spinal Circuits in Spasticity by Direct Dorsal Root Stimulation

Abstract

Experimental researchers have shown that, because of normal inhibitory processes, repetitive orthodromic stimulation of the dorsal spinal roots induces a depression of the reflex discharge in the spinal motoneurons that is a function of the stimulation rate. Because a lack of inhibitory processes is considered to be the basic mechanism of spasticity, intraoperative stimulation of dorsal spinal roots from L-1 to S-1 bilaterally was performed in 80 patients affected by cerebral palsy. In these patients spasticity (exaggerated stretch reflexes, marked increase of proprioceptive reflexes, and clonus) was the main symptom. We stimulated the dorsal roots adjacent to the spinal cord and recorded motor responses by electromyogram (EMG) in the corresponding muscle groups. The most important findings were that: (a) variable inhibition (diminished, increased, or normal) was encountered in the spinal circuits of the spastic patient; and (b) the individual roots and rootlets can have different effects upon segmentary output. The absence of normal inhibitory processes was the most common finding; surgical sectioning of the corresponding roots resulted in immediate reduction in muscle tone in the related muscles. Selecting the dorsal roots for section results in a remarkable reduction of negative side effects that may follow total or random rhizotomy (marked hypotonia, ataxia, sensory defects) and of the percentage of late recurrences. This procedure results in additional positive effects at segmentary and suprasegmentary levels. These results confirm the idea that the basic mechanism of spasticity is a central defect in the traffic regulation of peripheral afferents as they are transmitted to the spinal cord. This defect causes segmentary and suprasegmentary adaptive reactions that extend the negative outcome of the local increase of muscle tone.

Selective Posterior Rhizotomy and Intrathecal Baclofen for the Treatment of Spasticity

“…In the 1970s, Fasano et al [5, 19]described selective posterior rhizotomy based on electromyographic responses to repetitive electrical stimulation. This technique was based on animal work which showed that monosynaptic reflex responses become progressively depressed by rapidly repeated stimulation of afferent fibers [20, 21, 22].…”

“…The depression was thought to be due to presynaptic inhibition. Fasano et al [19]stimulated lumbosacral posterior nerve rootlets at the level of the conus medullaris in spastic children at increasing frequencies and recorded the responses from anterior roots and muscles. Stimulation at certain rootlets was associated with what was felt to be an inhibitory response, whereas others lacked the features of inhibition or were associated with exaggerated motor responses such as sustained discharges or spread of contraction to other muscle groups.…”

“…Stimulation at certain rootlets was associated with what was felt to be an inhibitory response, whereas others lacked the features of inhibition or were associated with exaggerated motor responses such as sustained discharges or spread of contraction to other muscle groups. Fasano et al [19]postulated that abnormal interneuronal control of Ia afferents was involved in abnormal inhibition. They divided the rootlets associated with exaggerated responses, resulting in 25–50% of rootlets cut in most cases [19].…”

“…Fasano et al [19]postulated that abnormal interneuronal control of Ia afferents was involved in abnormal inhibition. They divided the rootlets associated with exaggerated responses, resulting in 25–50% of rootlets cut in most cases [19]. Favorable results were noted in 80 children with spastic cerebral palsy who where followed for 15 years postoperatively [23, 24].…”

“…Foerster [14]published pre- and postoperative photographs of his patients in his 1913 series, and Fasano et al [5, 19, 24]and Fasano and Broggi [23]recorded their patients on film. The first set of patients evaluated in a more stringent fashion is reported in the Cape Town series.…”