Chapter 4 - Juvenile Idiopathic Myoclonic Epilepsy (Janz Syndrome) as a System Epilepsy Affecting the Corticothalamic System and the Frontal Motor and Cognitive Frontal Subsystems

Abstract

Juvenile idiopathic myoclonic epilepsy (JME) starts in adolescence and young adulthood. Antiepileptic drugs, especially valproic acid, result in permanent freedom from seizures; however, reducing and stopping medication may lead to the recurrence of seizures. The typical seizure types are myocloni with no disturbance of consciousness, generalized tonic–clonic, and absence seizures. Reflex seizures—induced by a consistent triggering stimulus—occur in 50% of patients, and a reflex mechanism probably underlies many “spontaneous” seizures. There are four types of reflex epileptic features: (1) genetic photosensitivity (Wolf and Goosses, 1986) in the form of “photoparoxysmal response,” affecting up to 90% of JME patients (Appleton et al., 2000); (2) sensitivity to eye closure (fixation off activity), 15%–20% of patients; (3) orofacial reflex myocloni, presenting as rapid small jerks in the perioral muscles, activated by language-related activities; and (4) praxis-related reflex epilepsy (Matsuoka et al., 2000; Yacubian et al., 2014). Similar to absence epilepsy, a dysfunction of the corticothalamic system underlies JME, but clinical and neuroimaging data suggest the participation of motor and cognitive networks in JME. In the section “Reading Epilepsy,” we include a related (spectrum) condition, featured by orofacial reflex myocloni (Yacubian et al., 2015), affecting 25%–30% of JME patients (Salek-Haddadi et al., 2009). The genetically determined hyperexcitability of the speech network underlies reading epilepsy; reading or any verbal activity may trigger a seizure. Idiopathic generalized epilepsy is not a tenable construction any more, and the multilevel incongruence regarding the EEG, seizure semiology, and genotypic features of JME obstructs its clear classification.