Inter-session repeatability of cortical excitability measurements in patients with epilepsy

Previous studies have evaluated the inter-session variability of motor thresholds (MT), short intracortical inhibition and intracortical facilitation using paired pulse transcranial magnetic stimulation (TMS) in normal individuals. Here we evaluate the reproducibility of a range of measures of cortical excitability in patients with epilepsy.

Twenty-four drug naïve patients with newly diagnosed epilepsy (13 idiopathic generalised epilepsy [IGE], 11 focal epilepsy) and seventeen non-epilepsy controls were studied. Motor threshold (MT) at rest and recovery curves constructed using paired pulse stimulation at short (2-15 ms) and long (50-400 ms) interstimulus intervals (ISIs) were analysed on two separate occasions, 4-20 weeks apart. The Lin's concordance correlation coefficient test was used to measure agreement between the two sessions.

Significant levels of agreement between the two sessions were observed at MT and all the ISIs measured. This was highest in non-epilepsy controls.

Cortical excitability measures are repeatable over time in both patients with epilepsy and healthy controls. Increased motor cortex excitability is a stable feature in epilepsy without significant inter-session variability.