Perhaps the most common medical test obtained in patients with epilepsy is the EEG (electroencephalogram). This test is done to look for abnormal electrical activity associated with epilepsy and it can also indicate how effective (or not) treatment is.
It is not so clear at this time the value or need for EEGs in patients on dietary therapy. The 2009 International Consensus Statement generally recommended an EEG before starting the diet as a baseline, mostly to help clarify why the epilepsy is happening, yet it is still "optional". While on the diet an EEG is only "optional" as well, although 35% of centers including our s will check an EEG after 6-12 months to compare to pre-diet. It may not necessarily change management, but an EEG can serve as a way to confirm the reduction in seizures that parents may be noticing. In patients who are in status epilepticus, the EEG may be the only guide to prove the diet helped.
The effect on the EEG of dietary therapy is very controversial, and a recent study by Dr. Sudha Kessler and colleagues from Children's Hospital of Philadelphia has added to the information available. In this study, the authors found that sophisticated techniques to look at the number of EEG spikes identified a link: if the spikes were at least 10% reduced, the likelihood of a child having >50% reduction in seizures was 6 times higher. This correlation was seen very early with the EEG done after 1 month.
Previous research has shown generally similar results. A study in 2007 by Dr. Tove Hallbook looked at children on the diet at 3 months. Similarly the reduction in seizures correlated with a reduction in EEG spikes, but this was mostly seen during sleep.
What about in epilepsy syndromes? Studies have shown that if the KD helps eradicate infantile spasms, the EEG findings (hypsarrhythmia) will resolve too. This is probably true as well for absence epilepsy. However, some studies have not shown a clear link overall. Dr. Freeman's randomized and controlled study of the ketogenic diet for Lennox Gastaut syndrome showed a trend towards improvement with the ketogenic diet and saccharin (vs. the ketogenic diet with glucose/sugar). However, the change in EEG was nearly non-existent, leading Dr. Freeman to write an editorial in Epilepsia, highlighting that EEG changes are not the same as clinical seizures, and may respond differently to therapy. As well, the group from Denmark in 2009 looked at children with "CSWS" (continuous spike wave during sleep), a very difficult epilepsy syndrome to treat. Only 1 of 5 children had significant improvement in their EEG findings, leading the authors to state that "the ketogenic diet does not alter the course of CSWS."
In summary, I think the EEG can be a help for children on the ketogenic diet, but as long as it's put into the context of how the child is doing clinically. If a child is apparently doing well and the EEG confirms that (perhaps using these new sophisticated spike counts), then maybe medications can be slowly withdrawn? If a parent thinks a child is seizure-free but is unsure, then an EEG might clinch it. Additionally, if a child is still having frequent seizures, but the EEG shows improvement, then a keto team might agree to give the diet more time.
- Kessler SK, Gallagher PR, Shellhaas RA, Clancy RR, Bergqvist AG. Early EEG improvement after ketogenic diet initiation. Epilepsy Research 2011;94:94-101.
- Hallbook T, Kohler S, Rosen I, Lundgren J. Effects of ketogenic diet on epileptiform activity in children with therapy resistant epilepsy. Epilepsy Research 2007;77:134-140.
- Freeman JM. Seizures, EEG events, and the ketogenic diet. Epilepsia 2009;50:329-330.
- Nikanorova M, Miranda MJ, Atkins M, Sahlholdt L. Ketogenic diet in the treatment of refractory continuous spikes and waves during slow sleep. Epilepsia. 2009;50:1127-31.