Cortical excitability in patients after loading doses of lamotrigine: A study with magnetic brain stimulation

Purpose: Transcranial magnetic stimulation (TMS) of the brain allows the ph armacologic effects of anti-convulsant drugs (AEDs) on the excitability of motor corticospinal pathways to be evaluated in patients with epilepsy and normal subjects. However, no study has yet documented the changes in motor excitability in patients treated with lamotrigine (LTG). We aimed to study the effects of loading doses of LTG on TMS recordings in patients with epil epsy at the beginning of their treatment. Methods: We investigated single-pulse TMS in six patients with complex part ial seizures. The TMS recordings were performed in five sessions before and during 5 weeks of treatment. Motor threshold, motor-evoked potential (MEP) amplitude, cortical silent period, and peripheral conduction velocity were used as parameters of evaluation. LTG was started with a dosage of 25 mg/d ay until a daily maintenance dosage of 200 mg/day was reached. Results: The motor threshold activation of thenar muscles was significantly increased by LTG after 2 weeks of treatment and was increased in a paralle l way to the loading dose of the drug at week 3 and 5 of treatment. The MEP size recorded from the thenar muscles did not show significant changes at high- or low-intensity stimulation. The cortical silent period remained unc hanged at low- and high-intensity stimulation. The absolute latency of MEPs after cortical and cervical stimulation was unchanged, as was the central motor conduction time. Conclusions: Our study documents that loading doses of LTG, administered as monotherapy, progressively increases patients' motor thresholds over short periods.