Localization in epilepsy-making the diagnosis

In this post I shall explain in simple terms how a diagnosis of epilepsy is made by neurologists. First to get a few terms clarified:

The terms “Seizure disorder” and “Epilepsy” are frequently used interchangeably. They both mean the same. The person who is diagnosed with “epilepsy” or “seizure disorder” has a condition which makes him/her prone to having multiple seizures in his lifetime. Another way to put this is a follows. If you are diagnosed with epilepsy, it means that more than likely you shall suffer seizures in your lifetime if you do not take anticonvulsant therapy (anti seizure medication).

Remember any of us can suffer a seizure but it does not mean we have epilepsy. Let me explain with the aid of an example. Think of a person who suffers a seizure because he drank too much or consumed an illicit drug such as cocaine. Now this person has certainly suffered a convulsion/seizure but he does not necessarily have epilepsy. This person has suffered a seizure provoked by an illicit drug. If this person does not consume excess alcohol again/ avoids illicit drug; he may never suffer another seizure in his lifetime. Contrast this with a patient who has epilepsy. The person who has epilepsy is predisposed to having seizures in his lifetime (he/she has an inherent predisposition to seizures-at times this inherent predisposition is due to genetic causes. Other times it may be on account of other causes such as a brain tumor, a vascular (blood vessel) malformation in the brain, a cyst in the brain, due to prior head trauma/injury, due to an old history of meningitis or encephalitis).

So how is the diagnosis of epilepsy made by neurologists. Well when a patient presents to us with a history of seizure; we first attempt to collaborate the history with additional history from the family (preferably someone who may have witnessed the convulsion). This is important because it helps us to distinguish a seizure from seizure mimics such as fall with loss of consciousness, fainting and other causes of confused behavior with or without loss of consciousness. So first and foremost the diagnosis of epilepsy is made based on a good history. As I sometimes tell my patients, I do not want to “miss” a diagnosis of epilepsy (as seizures are associated with falls, injury and sometimes can cause sudden death). At the same time, I do not want to “over-diagnose” someone with epilepsy (as patients usually have to take anticonvulsant drugs for a long time and these drugs do have side-effects). Herein lies the importance and value of good history taking.

Next come the tests which help to “confirm” the diagnosis of epilepsy. Two tests are commonly carried out. A MRI of the brain is usually carried out to rule out “secondary” causes of epilepsy such as brain tumor, cyst, vascular malformation of the brain, look for “scars” of prior head injury or infections. The second test which is carried out is an electroencephalogram (also called a EEG). This test is carried out to look at the brain waves and identify where in the brain (right Vs left side of brain, which part of the brain) is the “misfiring” coming from. The above two tests in conjunction with history help to confirm the diagnosis of epilepsy.

Nitin K Sethi, MD

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