A letter to the editor in response to the article "Transcranial Motor-Evoked Potentials Combined With Response Recording Through Compound Muscle Action Potentials as the Sole Modality of Spinal Cord Monitoring in Spinal Deformity Surgery," by Hsu, Cree, Lagopolous and Cummine is presented.
Journal Of Clinical Neurophysiology: Official Publication Of The American Electroencephalographic Society [J Clin Neurophysiol] 2013 Aug; Vol. 30 (4), pp. 382-5.
Adolescent, Anesthesia statistics numerical data, Child, Electric Stimulation instrumentation, Electric Stimulation methods, Electroencephalography, Extremities physiology, Humans, Motor Cortex physiology, Motor Neurons physiology, Retrospective Studies, Scoliosis etiology, Scoliosis surgery, Spinal Fusion methods, Spinal Muscular Atrophies of Childhood complications, Evoked Potentials, Motor physiology, Extremities physiopathology, Motor Cortex physiopathology, and Spinal Muscular Atrophies of Childhood physiopathology
Spinal muscular atrophy is a progressive condition in which movement is gradually lost as a result of the loss of spinal motor neurons. Individuals with this condition may require surgical correction of a secondary scoliosis. Motor evoked potentials were recorded using transcranial electrical stimulation in four such individuals undergoing surgery. All the patients were nonambulatory and in wheelchairs. Motor evoked potentials were recordable in both upper and lower limb muscles, with similar stimulation parameters to control subjects undergoing surgery for idiopathic scoliosis. The amplitudes of the motor evoked potentials were similar to those in control subjects, although the latencies were shorter reflective of the smaller stature of the spinal muscular atrophy patients. The relative preservation of the motor evoked potentials despite the patients' poor voluntary motor control suggests that there is a selective preservation of the motor neurons mediating the motor evoked potential in spinal muscular atrophy and a maintenance of the conduction velocities of the corticospinal tract.
Study Design: Clinical trial. Objective: To compare the efficacy of a commercially available stimulating pedicle probe with a custom-made probe for the detection of pedicle wall breaches during screw insertion for the surgical correction of scoliosis. Summary Of Background Data: Stimulus triggered electromyography has been used to detect small breaches in the walls of the spinal pedicles during pedicle screw insertion. We routinely use a reusable, custom-made clip that can be attached to the screw, pedicle probe, or other instruments. Commercial systems are available in which the instrument is electrically instrumented to deliver current. Methods: In five patients (173 pairs of tests), we compared the threshold current required to trigger an electromyographic response during testing of the pedicle. Each track or screw was tested with both the custom-made and the commercial probe and the threshold current recorded. Results: Both systems were able to detect pedicle wall breaches using triggered electromyography. The threshold current recorded was not significantly different between the two systems (P > 0.1, paired t test) nor was the difference (0.16 mA) clinically significant. Conclusion: No difference was found between the thresholds detected with either system. There is however, a significant difference in the costs of the two probe systems.
Primary orthostatic tremor is characterized by 16-Hz motor activity that is coherent between muscles. It has been suggested that this tremor originates in the brain. This view is questioned by findings from a patient with complete paraplegia who experiences intermittent leg spasms at rest. The EMG activity within the spasms showed a 16-Hz component that was coherent between muscles unilaterally and bilaterally. This raises the possibility that the spinal cord could be the source of orthostatic tremor.