The diagnostic reliability of magnetically evoked motor potentials in multiple sclerosis

In a prospective study, we evaluated the technique of magnetically evoked motor potentials (MEP) in the diagnosis of multiple sclerosis (MS). We consecutively included 68 patients with symptoms or signs compatible with a demyelinative CNS affection. We subjected all patients to CSF analysis, MRI studies of the brain and brainstem, visual evoked potentials (VEP), brainstem auditory evoked potentials (BAEP), and somatosensory evoked potentials (SSEP). We then used the results to categorize the patients according to the Poser criteria of multiple sclerosis. Blinded from the results of the above investigations, one of the authors made MEP recordings from three muscles in the upper limbs and two in the lower limbs in all 68 patients. Forty patients received an MS diagnosis, and in these, MRI was positive in 88%, MEP in 83%, VEP in 67%, SSEP in 63%, and BAEP in 42%. As to the diagnosis of MS, the reliability of a prolonged central motor conduction time (CMCT) was 0.83 (0.73 to 0.93), while the reliability of a normal CMCT was 0.75 (0.61 to 0.98). The information gained by MRI was best supplemented by VEP. Of the neurophysiologic tests, the MEP was in closest agreement with the MRI with a concordance of 85%.