The spinal stretch reflex arc can be interrupted at the level of the spinal cord. McCarty and Kiefer123 first described the cordotomy procedure in 1949. Because this radical procedure often had undesirable effects such as sensory loss and worsened bladder function, it is no longer preformed to treat spasticity.
The longitudinal myelotomy was introduced in 1951 by Bischof.124 To avoid damaging descending motor pathways, he later modified this procedure from a lateral to a dorsal longitudinal myelotomy.125 Laitinen et al.126 used this procedure in patients with spinal cord injury, cerebral palsy (CP), and multiple sclerosis (MS). Spasticity was relieved in 8 of 9 patients but recurred over time. Transient bladder dysfunction and permanent sensory deficits also occurred. Moyes127 reported that 19 of 21 patients who underwent longitudinal myelotomy had good results. This procedure has been recommended for patients with severe spinal cord injuries or diseases with severe intractable, bilateral, lower-extremity spasticity.128
In 1986, Sindou et al.129 modified the selective dorsal rhizotomy such that afferent fibers were divided as they entered the spinal cord in the dorsal root entry zone (DREZ). This DREZotomy consists of a 3-mm–deep microsurgical incision directed at a 45-degree angle in the posterolateral sulcus at the involved spinal levels. This incision destroys nociceptive and myotatic fibers but spares the lemniscal fibers, thus interrupting the spinal reflex arc and nociceptive pathways. Although originally performed in adult hemiplegic patients with severe upper-extremity spasticity, favorable results were reported in 121 patients treated with microsurgical DREZotomy for lower-extremity spasticity.128,130
Such stereotactic procedures as pallidotomy, pulvinolysis, and ventrolateral thalamotomy are used to treat extrapyramidal disorders characterized by involuntary movements and fluctuations in tone. The basal ganglia modulate motor activity, forming the center of a looping circuit between cortical motor areas and thalamus. Basal ganglia diseases may release inhibition and thereby result in abnormal movements. Stereotactic thalamotomy can reduce unilateral tremor, athetosis, and chorea, but it is not effective for spasticity.128,131–133
Interrupting outflow from the dentate nucleus (dentatomy) by stereotactic cerebellar lesions can diminish muscle tone by reducing the unbalanced facilitatory influences on the ventral horn cells. Gornall et al.133 reported improvement in 5 of 6 children with spastic CP who underwent stereotactic dentatomy. However, Guidetti and Fraioli134 reported a series of dentatomies in 47 patients and noted some improvement in dystonias but little effect on spasticity. Siegfried et al.135 observed that dentatomy may reduce spasticity in some cases. Overall, stereotactic procedures have not proven very effective in spastic conditions.128
Chronic cerebellar stimulation was initially reported by Cooper et al.136 in 1976 to increase inhibitory outflow on the ventral motor neurons. Cooper’s group implanted a subdural electrical stimulator on the surface of the cerebellum as a “pacemaker” to decrease the extensor hypertonia in patients with spastic CP. In 1980, Davis et al.137 reported on a series of 262 patients, 230 of whom had spastic CP and underwent chronic cerebellar stimulator implantation. The primary effect was a lowering of spastic muscle tone in 90% of patients. Six months postoperatively, 25 patients were out of their wheelchairs and another 47 had improved ambulation. Davis’s group138 later conducted a double-blind trial in 33 patients, of whom 75% enjoyed qualitative improvement in spasticity and function. Other groups, however, could not demonstrate consistent successful reductions in spasticity with chronic cerebellar stimulation.136,138–141 Harris et al.142 reported a series of 13 children with CP with up to 14 years of follow-up and concluded that cerebellar stimulation was initially effective in reducing hypertonicity but that effectiveness decreased significantly after 3 to 5 years. Although some groups still advocate chronic cerebellar stimulation,143,144 this procedure rarely is used to manage spasticity.128
Dorsal spinal cord stimulation was introduced to treat chronic pain disorders but was found also to improve motor function in a patient with MS and to reduce painful spasticity in a patient with metastatic spinal disease.145 Subsequent experience with chronic epidural spinal cord stimulation varies. Quantitative measures of spasticity improved in one series of 48 patients with spinal cord injury.146 In another series of 17 patients, however, only 1 patient gained long-term relief of spasticity.147 Cervical spinal cord stimulation can reduce spasticity on functional, neurophysiologic, and subjective measures,148,149 but its rare use suggests that clinically significant benefits are uncommon.
Reviewed and revised May 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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