Myoclonus cortical generators in Unverricht-Lundborg disease: an electric source imaging study

Purpose: To localize the cortical generator of myoclonic jerks in progressive myoclonic epilepsy (Unverricht-Lundborg disease) applying the Electrical Source Immaging method (ESI). Method: 3 patients (2 female, 1 male, age: 17–48 yrs) affected by Unverricht- Lundborg disease underwent a 256—channels EEG with concomitant polygraphic recording. Provocative manouvres were conducted during the exam to elicit myoclonic jerks. EEG (electroencephalographic) and EMG (electromyographic) traces were analyzed off line. For the other 2 patients, a back-averaging of the myoclonic EMG activity and corresponding EEG abnormalities was performed. Analysis was conducted off line. A mean of 15 jerk-locked EEG potentials for each patients were averaged, and projected through a LORETA algorithm on an MNI (Montreal Neurological Institute) brain template in order to identify the cortical generator. Result: Jerk-locked EEG potentials were recognizable over the centrofrontal derivations, with a slight lateralization in each single case. ESI elaboration localizes the cortical generator over the anterior premotor frontal cortex (pt 1: Brodman area 6, pt 2: Brodman area 10; pt 3: Brodman area 11), with a lateralization concordant with the EEG potentials (2 right hemisphere, 1 left). Conclusion: ESI is a technique that permits cortical source localization of EEG potentials. Its application to this rare form of epilepsy depicts the important role of the pre-motor and frontal cortex in the myoclonic jerk's generation. To our knowledge, this is the first report describing the cortical source generation from the anterior/premotor cortex. Since only the jerk-locked potential was examined, we can not infer on the involved networks.