The diagnostic value of motor evoked potentials

Objective: To assess the diagnostic usefulness of motor evoked potentials ( MEPs) and to identify the optimal method for calculating the central conduc tion time. The test results were evaluated in a prospective study of 1023 n eurological patients. Methods: We evaluated the correlation between clinical and electrophysiolog ical findings, the accuracy, the sensitivity, the percentage of subclinical abnormalities and the false negative rates of MEPs in different neurologic al disorders. In patients with lower motor neuron involvement, we compared the central conduction time calculated as the difference between the latenc y of the cortical and magnetic root stimulation responses with that calcula ted using the F-wave method. Results: The agreement index between electrophysiological and clinical find ings was 87%. The overall accuracy of the test was 0.97. The higher sensiti vity values were demonstrated in spinal cord disorders (0.85), hereditary s pastic paraplegia (0.80) and motor neuron diseases (0.74). The higher perce ntages of subclinical abnormalities were found in motor neuron disorders (2 6%) muscular diseases (24%), multiple sclerosis (13.5%) and spinal cord dis eases (12.5%). The higher false negative rates were found in sylvian stroke (0.36) and hereditary spastic paraplegia (0.16). Central conduction study using magnetic paravertebral stimulation but not using the F-wave method, r esulted in 12% and 10% of false positive values in lower limb multiradiculo pathies and in neuropathies, respectively. Conclusions: MEPs represent a highly accurate diagnostic test. MEP clinical value is maximum in motor neuron, muscle and spinal cord diseases. In pati ents with lower motor neuron involvement, the gold standard for central con duction determination is the F-wave method. (C) 1999 Elsevier Science Irela nd Ltd. All rights reserved.