2023 Volume 51 Issue 2 Pages 51-56
Benign adult familial myoclonus epilepsy (BAFME) is one of the common diseases, that cause cortical reflex myoclonus (CM), especially manifesting rhythmic tremor as cortical tremor. Electrophysiologically, BAFME patients show features of cortical hyperexcitability, i.e., enlarged P25 or N35 amplitudes in somatosensory evoked potentials (giant SEPs), long-loop reflex (C-reflex), and spikes preceding myoclonus by a jerk-locked back averaging method. In EEG, they generally have interictal epileptiform discharges, photo-paroxysmal response, and increased amplitude and sharpness of background activities (anecdotally called “spiky alpha”). These findings suggest a cortical origin of the myoclonus. However, there had been no useful diagnostic biomarkers that could differentiate BAFME from other CM diseases. Recently, we revealed that high-frequency oscillations superimposed on giant SEP P25 (P25-HFOs) could be a reliable biomarker for the diagnosis of BAFME. We analyzed 49 CM patients (16 with BAFME and 33 with other CM) with giant SEPs. BAFME was reliably diagnosed using P25-HFOs with high sensitivity (100%) and specificity (87.9%). P25-HFOs may reflect cortical hyperexcitability partly due to paroxysmal depolarization shifts in epileptic neuronal activities and higher degrees of tremulousness than those in other CM. We also compared EEG posterior background activities between BAFME and other CM. BAFME patients had significantly higher beta power in the posterior area, which may be responsible for the appearance of “spiky alpha” and this could be a convenient biomarker for diagnosing BAFME. We introduce an overview of widely utilized new diagnostic biomarkers of BAFME distinct from other CM.
