Connectivity of the supplementary motor area in juvenile myoclonic epilepsy and frontal lobe epilepsy.
OBJECTIVE
Subtle structural abnormalities of frontal lobe gray and white matter have been described in cryptogenic frontal lobe and idiopathic generalized epilepsies. The supplementary motor area (SMA) has a role in motor control, and its involvement during frontal lobe epileptic seizures is characterized by a typical asymmetric tonic posturing. Moreover, motor networks are dysfunctional in juvenile myoclonic epilepsy (JME). We tested the hypothesis that SMA structural connectivity is altered in focal frontal lobe epilepsy (FLE) and JME compared to healthy controls.


METHODS
Diffusion tensor imaging (DTI) and probabilistic tractography were used to map the structural connectivity of the SMA, defined by motor functional magnetic resonance imaging (MRI), in 15 patients with JME, 36 patients with FLE, and 18 healthy controls.


RESULTS
Structural connectivity of the SMA was significantly reduced in JME compared to controls (reduced fractional anisotropy and increased mean diffusivity). In FLE there was no significant difference compared to controls, and in all groups there was stronger connectivity in the left hemisphere (higher fractional anisotropy) compared to the right. There was no difference in SMA connectivity between patients with medial or lateral frontal lobe epileptic foci.


CONCLUSIONS
Reduced white matter connectivity is the structural correlate of functional frontal lobe abnormalities in JME. In FLE, the structural connectivity of the SMA was preserved, suggesting a robust motor network that is not compromised by longstanding epilepsy involving the medial frontal lobes.
National Society for Epilepsy MRI Unit, Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology and National Hospital for Neurology and Neurosurgery, Queen Square, London, United Kingdom.
Serge
S
Vulliemoz
Christian
C
Vollmar
Matthias J
MJ
Koepp
Mahinda
M
Yogarajah
Jonathan
J
O'Muircheartaigh
David W
DW
Carmichael
Jason
J
Stretton
Mark P
MP
Richardson
Mark R
MR
Symms
John S
JS
Duncan
D000328:Adult; D001931:Brain Mapping; D038524:Diffusion Magnetic Resonance Imaging; D004292:Dominance, Cerebral / Q000502:physiology; D004569:Electroencephalography; D017034:Epilepsy, Frontal Lobe / Q000175:diagnosis / Q000503:physiopathology*; D005260:Female; D005625:Frontal Lobe / Q000503:physiopathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D020190:Myoclonic Epilepsy, Juvenile / Q000175:diagnosis / Q000503:physiopathology*; D009415:Nerve Net / Q000503:physiopathology; D011597:Psychomotor Performance / Q000502:physiology; D012815:Signal Processing, Computer-Assisted