Electroclinical features of myoclonic-tonic and spasm-tonic seizures in childhood

Myoclonic-tonic (MT) and spasm-tonic (ST) seizures represent distinctive features in late infantile epileptic encephalopathy (LIEE). This commentary aims to delineate the electroclinical characteristics of MT and ST seizures, setting them apart from other seizure types. Our analysis encompasses 211 ST and MT seizures observed in 31 patients diagnosed with LIEE, providing a comprehensive overview of video-EEG features and polygraphic signatures. In MT seizures, EEG findings reveal a high-voltage diffuse spike/polyspike and wave discharge, often succeeded by diffuse electrodecrements. The amplitude-integrated EEG (aEEG) signature is described as a “reversed checkmark.” Conversely, ST seizures exhibit EEG findings such as a vertex positive deflection after a slow-wave and relative electrodecrement, with intermixed epileptiform discharges. In comparison to MT seizures, polygraphic characteristics in ST seizures appear more distinct, featuring a brief rhomboid shape corresponding to the spasm, followed by a lengthier rectangular shape indicative of the tonic phase of the ST seizure. While the pathophysiology of ST and MT seizures remains inadequately understood, their concurrent occurrence and association with other seizure types (tonic, epileptic spasm, myoclonic) within the temporal context of LIEE and other epileptic encephalopathies prompt us to anticipate advancements in our understanding through future research. We hope that this study serves as a foundation for unraveling these complexities in the times to come.