Detection and treatment

Dr. John S. Duncan is Professor of Clinical Neurology, Institute of Neurology and Medical Director, National Society for Epilepsy, United Kingdom. He delivered the 15th K. Gopalakrishna Endo-wment Lecture at the Indo-British workshop in Chennai. His research interest includes structural and functional imaging of the brain, genetic basis of epilepsy and the measurement of treatment outcome. He spoke to Asha Krishnakumar on the technique to detect and treat epilepsy and ongoing research in the area. Excerpts from the interview:

What techniques are used to detect epilepsy and its causes?

The one that is commonly used today is magnetic resonance imaging (MRI), developed at Nottingham University, U.K., 20 years ago. It was first used in the early 1980s to get pictures of the brain and then in 1984 to detect epilepsy. Prior to this, brain i maging was done using invasive methods such as angiography and air encephalography, followed by X-ray CT (computerised tomography) in the late 1970s.

X-ray CT was a significant development in non-invasive investigation. It could "see" only large tumours and strokes, but nothing smaller than a few centimetres. MRI revolutionised investigation and treatment of epilepsy. For the first time it was possibl e to see details of the brain structure - whether a part of the brain was malformed - and detect small blood leaks, small tumours, small strokes, or small abnormalities such as tuberculosis, which could cause epilepsy. Any small damage to the hardware ca n give rise to this problem. An MRI scan can detect the minutest of damage in any part of the brain.

If patients do not respond to drugs, surgical treatment is a possibility. This is done by removing that part of the brain which causes the seizures. But that can be done only after identifying the part that is causing the trouble. An MRI scan is very use ful in this regard as it can detect even small scars causing the trouble.

It is also possible to use an MRI scan to measure the concentration of certain chemicals in the brain. This is important because for most people for whom epilepsy is not caused by problems in the brain structure, it is chemical imbalance that causes it. The nerve cells of the brain send chemical messages to one another. During an epileptic attack there is an imbalance in some of these chemicals.

There are two main categories of these chemicals. One is inhibitory, which is less active, and the other is expansitory, which is excitable. We believe there are some parts of the brain that may get too much excitement, and risk being overactive and get short-circuited leading to seizure. In these cases, an MRI scan is not useful. We use MR spectroscopy to measure the concentration of these chemicals. This can be done entirely safely now.

The Positron Emission Technology (PET) gives the functional image of the brain as against an MRI, which gives images only of the brain structure. It is used primarily for research purposes; its application for clinical purposes is relatively small as it is very expensive.

What data do these techniques provide and how are they useful in the diagnosis and treatment of epilepsy?

These techniques are not useful by themselves but only when they are interpreted. They give information on the parts of the brain that are affected, the parts that are working, the kind of seizures that occur, what happens electrically when seizures occu r (that can be got by electroencephalography - EEG), and the image of the brain structure and functions. With all these inputs, the causes and treatment can be worked out. There are several kinds of epilepsy, each with specific causes and needing differe nt treatment.