Facilitation of rhythmic events in progressive myoclonus epilepsy: a transcranial magnetic stimulation study

Twelve subjects with progressive myoclonus epilepsy (PME) were studied with transcranial magnetic stimulation (TMS), using single and paired magnetic stimuli at different interstimulus intervals (ISIs), and polygraphic record ing. Motor threshold (T) and silent period (SP) were normal. Paired TMS sho wed a loss of inhibition at 100-150 ms ISI and a marked facilitation at 50 ms ISI of conditioned motor evoked potential (MEP). Polygraphic analysis sh owed 20 Hz oscillatory activity over the sensorimotor area coupled to contr alateral myoclonic jerks. These findings suggest a condition of increased s upraspinal excitability and support the evidence of a cortical rhythm in th e range of 20 Hz. No direct evidence exists that these findings are mediate d by the same intracortical pathway. Furthermore, the normal SP and T sugge st that the abnormal excitability is not a constant feature but is evident during rhythmic events. (C) 1999 Elsevier Science Ireland Ltd. All rights r eserved.