A surgical team at Beaumont Hospital has been able to measure chemical changes in the brain of a patient experiencing an epileptic seizure. The research provides important information about brain chemistry, but more importantly it opens up new possibilities for diagnosis and treatment.
The technique, known as brain microdialysis, was first applied only three months ago but has already produced a wealth of data, according to the head of the research group, Prof Jack Phillips, consultant neurosurgeon at Beaumont Hospital and associate professor of surgery at the Royal College of Surgeons of Ireland.
Epilepsy is a condition where brain cells or neurons fire abnormally, causing mild or sever seizures. About 25,000 people in the Republic suffer from the disorder and most respond well to drug treatments. About 20 per cent, however, have "intractable epilepsy" that defies drug treatment.
A proportion of these would respond well to surgery. The new brain microdialysis technique provides a further powerful tool for identifying patients most suited to surgery.
"Dialysis is normally a word you use when we talk about kidney failure," Prof Phillips said. In kidney dialysis a machine is used to clear toxic substances from the blood, but brain dialysis provides a way to sample the brain's signaling chemicals known as neurotransmitters. "The principle of dialysis is being applied to the brain for the first time."
The technique involves the use of a brain surface EEG (Electroencephalogram) which gives the surgical team a general area where abnormal brain cell firing is taking place. The EEG can narrow down a search area, "the seizure focus zone" to about five square centimetres, but the microdialysis technique can bring this down to about five square millimetres.
Once the surgical team knows where to look, it inserts a tiny catheter tube, like a fine needle about double the diameter of a human hair. It "can be inserted into the brain with minimal or no trauma", Prof Phillips said.
The tube is used first to inject a tiny amount of sterile water into the tissues. This mixes with the neurotransmitters and is then drawn back up the tube so the chemicals can be analysed.
The neurotransmitters of interest to the team are glutamate, which is released when brain cells are under stress, and the substance that inhibits glutamate, GABA. In epilepsy patients the balance between these two substances is lost and toxic glutamate predominates, a situation which can cause seizure.
The brain microdialysis technique applied at Beaumont by Prof Phillips and Dr Philip Thomas, clinical research fellow and neurosurgical resident, allows these two neurotransmitters to be measured accurately. The technique is a powerful way to identify epileptic patients suitable for surgery, particularly those with sclerosis of the hippocampus, which involves damage to a brain structure. If you can identify the right patients "you may have a cure on your hands", Prof Phillips said.
Brainwave, the Irish Epilepsy Association, can be contacted at (01) 455 7500.