Brief Answer:
Read below

Detailed Answer:
I read your question carefully and I understand your concern.

Seizure can have many different causes such as stroke, infections or inflammation in the brain, brain tumor, head trauma, alterations in blood components such as glucose or electrolytes etc. At times even after extensive testing no cause can be found. Since cat scan was normal (and I suppose you have done some other blood tests for other possibilities) I suppose your neurologist for now hasn't found an explanation (as I said it happens even when every test is done).

We usually do not start treatment only one first seizure since as I said it could be due to transitory metabolic changes which don't warrant treatment. However he must have found on EEG electric changes which indicate that you might be prone to having more seizures. So he didn't want to take a chance and put you on Keppra to prevent that from happening. The EEG doesn't indicate the precise cause at times it can indicate the site where electrical activity starts but even in that case not the precise cause, that's why he hasn't given you a diagnosis. He wants to follow up to check for other seizures and have a control EEG I suppose to decide whether continuation of treatment for a single seizure is necessary.

An MRI might also be scheduled especially if the EEG indicates a localized origin of your seizures.

I remain at your disposal for further questions.

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