Is Intraoperative Muscle Motor Evoked Potential Variability due to Fluctuating Lower Motor Neuron Background Excitability?

PURPOSE: This pilot study tests the contribution of fluctuating lower motor neuron excitability to motor evoked potential (MEP) variability. METHODS: In six pediatric patients with idiopathic scoliosis and normal neurologic examination, cascades of 30 intraoperative H-reflexes (HRs) and MEPs were evoked in the soleus muscle using constant-current stimulators and recorded through surface electrodes with a 20-second interstimulus interval. First, HRs were obtained with an intensity capable of evoking the maximum response. Subsequently, MEPs were obtained with double trains and an intensity of 700 to 900 mA. Coefficients of variation (CVs) of amplitude and area under the curve from HRs and MEPs were compared using a paired two-tailed Student t test. Coefficients of correlation between the mean CVs of HR and MEP parameters were also assessed. RESULTS: Pooling the results from the six patients, the mean CV of amplitude from the MEP (24.6 ± 3) was significantly higher than that from the HR (3.5 ± 4.4) (P = 0.000091). The mean CV of the MEP area under the curve (21.8 ± 4.8) was also statistically significantly higher than that from the HR area under the curve (3.4 ± 4.5) (P = 0.00091). The coefficients of correlation of the mean CV of the HR amplitude and area under the curve compared with the corresponding values of the MEP were low (r = 0.29) and very low (r = 0.03), respectively. CONCLUSIONS: Our results suggest that fluctuations in lower motor neuron excitability may be less important than previously thought to explain the magnitude of MEP variability. The efficacy of corticospinal volleys to recruit a larger and more stable lower motor neuron population would be critical to obtain reproducible MEPs.

A Multiparametric Alarm Criterion for Motor Evoked Potential Monitoring During Spine Deformity Surgery.

PURPOSE: This is a pilot study to compare changes in the amplitude, area below the curve, number of phases, duration, and latency of the intraoperative transcranial motor evoked potentials (TcMEP) for early detection of impending spinal cord injury. An empirical ratio calculated by a combination of the above-mentioned parameters was also assessed. METHODS: Intraoperative TcMEP recordings from five patients presenting with neuromuscular kyphoscoliosis, idiopathic scoliosis, achondroplasia and lumbar kyphosis, congenital kyphosis, and achondroplasia with cervical instability were reviewed. Anesthesia was sustained with propofol or sevoflurane plus remifentanil, no muscle relaxants were used after intubation. The TcMEPs to multipulse electrical stimulation were recorded from upper-limb and lower-limb muscles. To be worthy of analyses, changes should include TcMEP disappearance or amplitude decrease >-65% during surgical/force maneuverings. RESULTS: Transient TcMEP changes related to surgical/force maneuvering were observed in all five patients consisting of a decrease in the empirical ratio value (>-95%), followed in magnitude by a drop in the area below the curve, amplitude (>-80%), duration, and number of phases, whereas latency increased. Changes returned to baseline when maneuverings were reverted. No hemodynamic/anesthetic factors were present during these events. After surgeries, no new neurological deficits were detected. CONCLUSIONS: An empirical ratio accounting for all TcMEP parameters seems to drop more than the amplitude during an intraoperative event. As few cases were analyzed, further studies in larger series of patients will be necessary to assess empirical ratio sensitivity/specificity and to determine whether this may be a useful monitoring warning criterion not leading to unnecessary interference with surgical treatment.

Interferon beta-1a treatment in childhood and juvenile-onset multiple sclerosis.

The authors studied the safety and tolerability of subcutaneous interferon beta-1a at different doses in 24 children with clinically definite multiple sclerosis. After a mean treatment period of 44 months, interferon beta-1a was well tolerated in 22 patients, although two experienced possible serious adverse events. Although effectiveness cannot be inferred from this study, the authors did observe a significant reduction in the relapse rate at 22 mug, three times weekly, in the relapsing-remitting subgroup.

Motor activation time in Parkinson s disease

Se estudió el tiempo de activación motora (TAM), considerando para el presente trabajo como el intervalo de procesamiento intracerebral durante una prueba de Tiempo de Reacción (TR), en 17 pacientes con enfermedad de Parkinson y en 7 voluntarios sanos. El TAM fue calculado substrayendo al TR premotor los tiempos de conducción aferente y eferente obtenidos por medio de potenciales evocados somatosensitivos y motores. Comparados con los voluntarios sanos los pacientes con enfermedad de Parkinson presentaron valores de TAM significativamente prolongados (p < 0,02). En un grupo menor de 9 pacientes se estudiaron el TAM y el potencial cognitivo P300 mientras se encontraban bajo tratamiento antiparkinsoniano y también luego de un período de 12 horas de supresión medicamentosa. Durante el período de supresión los pacientes exhibieron un importante incremento en el TAM (P < 0,01) sin cambios significativos en la latencia o amplitud del potencial P300. Estos resultados sugieren que el enlentecimiento del TAM corresponde a un funcionamiento anormal de los circuitos dopaminérgicos involucrados en la iniciación del movimiento y no esté relacionado a cambios en la reactividad o en el estado cognitivo (AU)

Motor activation time in Parkinson 's disease

Se estudió el tiempo de activación motora (TAM), considerando para el presente trabajo como el intervalo de procesamiento intracerebral durante una prueba de Tiempo de Reacción (TR), en 17 pacientes con enfermedad de Parkinson y en 7 voluntarios sanos. El TAM fue calculado substrayendo al TR premotor los tiempos de conducción aferente y eferente obtenidos por medio de potenciales evocados somatosensitivos y motores. Comparados con los voluntarios sanos los pacientes con enfermedad de Parkinson presentaron valores de TAM significativamente prolongados (p < 0,02). En un grupo menor de 9 pacientes se estudiaron el TAM y el potencial cognitivo P300 mientras se encontraban bajo tratamiento antiparkinsoniano y también luego de un período de 12 horas de supresión medicamentosa. Durante el período de supresión los pacientes exhibieron un importante incremento en el TAM (P < 0,01) sin cambios significativos en la latencia o amplitud del potencial P300. Estos resultados sugieren que el enlentecimiento del TAM corresponde a un funcionamiento anormal de los circuitos dopaminérgicos involucrados en la iniciación del movimiento y no esté relacionado a cambios en la reactividad o en el estado cognitivo