Evil spirits and Epilepsy?

I asked this question as part of another but it didn't get answered.

In the Bible, one of the stories is Jesus heals a boy with an evil spirit. But my question isn't about the title's poor wording.

That boy apparently experienced the symptoms of epilepsy, and that symptom (the violent spasms and frothing at the mouth AT THE SAME TIME) is uncommon and is only caused by epilepsy.

So if that boy supposedly had an evil spirit, there are three possibilities:

1. Epilepsy is caused by evil spirits

2. Epilepsy has the same coincidental symptoms as an evil spirit. (Coincidence seems to come up a lot in the Bible, doesn't it?)

3. The Bible and Jesus were wrong/lying.

I know which the atheists are going to say, but what about Christians?