Valproate and EEG

Accuracy of EEG for Epilepsy detection

• Based on early studies, EEG results can show epileptiform activity in some normal brains
• On the other hand, only about 50% of patients with epilepsy will show epileptiform activity on a single EEG.
• Another author reviewing the literature found that first EEGs identify 29-55% of seizures, with follow up EEGs catching 80-90%.
• Thus, some EEG abnormalities in psychiatric patients may not be related to either epilepsy or the psychiatric disorder, and a normal EEG does not exclude the possibility of epileptic seizures.
• A meta-analysis revealed an increased risk of relapse in patients with abnormal versus normal EEGs, but failed to obtain reliable data on the importance of specific EEG features.
• Another longitudinal study in adult patients with partial epilepsies with multiple EEG studies before and at various time points during and after AED withdrawal confirmed the generally accepted view that an EEG should not be considered in the decision to withdraw an AED in patients with partial epilepsies.

Valporate and EEG

• In idiopathic generalized seizures, VPA decreased EEG synchronization in the delta and theta frequency bands in a use-dependent manner was supported
• VPA treatment normalizes EEGfC in IGE patients
• Half life of Epilim is around 8-20 hours. Epilim Chrono is a sustained release formulation, which shows less fluctuations in plasma concentrations.
• If an EEG is required without the affect of valproate, it is advisable for the drug to be stopped until its totally eliminated from the system (5 half  life = 97% eliminated)
• There is a variability in the elimination of Valproate (or other antiepileptic) based on individuals. Thus, the more accurate way to calculate elimination time is via doing a TDM and calculating the elimination half life specific for the patient.

References:

1. Jyoti Pillai and Michael R. Sperling. Interictal EEG and the diagnosis of epilepsy. Epilepsia 2006;47(supp. 1):15-6
2. http://www.epires-journal.com/article/S0920-1211%2814%2900275-7/abstract
3. http://www.sciencedirect.com/science/article/pii/S105913110700146X
4. Recurrence rate of seizure following discontinuation of anti-epileptic drugs in patients with normal long term electroencephalography. 2014
5. Effects of Antiepileptic Drugs on Electroencephalographic Findings in Patients with Idiopathic Generalized Epilepsy. Iranian Journal of Child Neurology 2011;5(4):33-36.