Abnormal Thalamocortical Structural and Functional Connectivity in Juvenile Myoclonic Epilepsy

Abstract and Commentary

By Nitin K. Sethi, MD

Assistant Professor of Neurology, Weill Cornell Medical College

Dr. Sethi reports no financial relationships relevant to this field of study.

Synopsis: In patients with juvenile myoclonic epilepsy, abnormal structural and functional connectivity was noted in the anterior thalamocortical bundle, as compared to healthy controls, and was correlated with the severity of the seizures.

Source: O’Muircheartaigh J, et al. Abnormal thalamocortical structural and functional connectivity in juvenile myoclonic epilepsy. Brain 2012;135:3635-3644.

Juvenile myoclonic epilepsy (jme), sometimes called Janz syndrome, is the most common idiopathic generalized epilepsy and is characterized by multiplicity of seizure types, including myoclonic jerks on awakening, generalized tonic-clonic seizures, and absence seizures. The interictal electroencephalogram is characterized by 4-6 Hz generalized spike wave and polyspike wave discharges with amplitude predominance bifrontally. Diffusion tensor imaging and functional magnetic resonance imaging show abnormal anterior thalamocortical bundle structural and functional connectivity in JME patients as compared to healthy controls.

The authors investigated thalamocortical structural and task (phonemic verbal fluency) modulated functional connectivity using diffusion tensor imaging and functional magnetic resonance imaging in 28 patients with JME and compared them to 38 healthy controls. Abnormal structural and functional connectivity was noted in the anterior thalamocortical bundle as compared to healthy controls. The authors further found that the degree of abnormal connectivity was related to disease severity. Patients with active generalized tonic-clonic seizures had greater degree of structural and functional connectivity dysfunction between the basal ganglia-thalamus-supplementary motor area/prefrontal cortex. The authors hypothesize that this dysfunction is the likely explanation of the frontal cortex dysexecutive, verbal and attentional neuropsychological impairments commonly seen in patients with JME.

Commentary

Previous studies have shown increases in blood oxygen level-dependent (BOLD) activity in the cortex and decreases in thalamic BOLD activity in patients with idiopathic generalized epilepsies and also a faster rate of thalamic volume loss in pediatric patients with idiopathic generalized epilepsies.1 The above study further strengthens the evidence for structural and functional dysfunction in the basal ganglia-thalamus-cortical (anterior frontal and premotor) loop in patients with JME and helps to explain the frontal lobe dysfunction and impairment in verbal and attention tasks in these patients.

Reference

  1. Hamandi K, et al. BOLD and perfusion changes during epileptic generalized spike wave activity. Neuroimage 2008;39:608-618.