Altered cortical inhibition in Unverricht-Lundborg type progressive myoclonus epilepsy (EPM1).
OBJECTIVE
Progressive myoclonus epilepsies (PMEs) comprise a heterogeneous group of conditions characterized by an imbalance between excitatory and inhibitory neuronal mechanisms. The aim of this study was to assess the function of the motor cortex in Unverricht-Lundborg disease (ULD), progressive myoclonus epilepsy type 1 (EPM1).


METHODS
Genetically verified EPM1 patients (n=24) were studied and compared with healthy subjects (n=24). MRI-navigated transcranial magnetic stimulation (TMS) was used to study the function of the motor cortex. Motor threshold (MT) and cortical silent period (SP) were used as parameters to evaluate cortical excitability. Peripheral muscle responses were recorded at the thenar and hypothenar using on-line electromyography (EMG).


RESULTS
The normal shortening of SP duration with age was not evident in EPM1. Thus, older patients exhibited significantly prolonged SPs in comparison to healthy control subjects (p<0.05). The MTs, measured as both stimulator output percentage and induced electric field strength (EF), were significantly higher in EPM1 patients than in control subjects (p<0.001). The stimulation of the thenar caused a co-activation in the hypothenar with significantly higher amplitudes as compared to controls (p<0.05).


CONCLUSIONS
The prolongation of the SPs with age in EPM1 patients suggests a prevailing inhibitory tonus of the primary motor cortex (M1) as possible reactive mechanism to the disease. Antiepileptic drugs may contribute to the increased MT but do not affect the SP. The results and methodology of this study can lead to a better understanding of the pathophysiology and progression of EPM1.
Danner
Nils
N
Department of Clinical Neurophysiology, Kuopio University Hospital and University of Kuopio, POB 1777, Kuopio FI 70211, Finland. danner@hytti.uku.fi
Julkunen
Petro
P
Khyuppenen
Jelena
J
Hukkanen
Taina
T
Könönen
Mervi
M
Säisänen
Laura
L
Koskenkorva
Päivi
P
Vanninen
Ritva
R
Lehesjoki
Anna-Elina
AE
Kälviäinen
Reetta
R
Mervaala
Esa
E