You are very lucky to have specialist place so close and a spinal tap is I believe common practice at the same time as the MRI. saves doing it later.
Epilepsy is a diagnosis that is made when nothing else shows and is fairly rare in cats.
I cant remember Riley having any other medical invasisve treatment recently like a dental?
Napoleon did not have epilepsy nor any problems in his brain but a brain infection that is thought caused an abcess to grow on the front of his head/brain. By being given injections of a powerful ab that worked in the brain, its thoughy that reduced or got rid of the abcess but it would come back. The vet thought the infection got in during a dental at his previous vets.
When he became ill with the blocked bladder he was having seizures again and one of the vets said that maybe we should try the abs for longer to see if it would completely go.......sadly we never got a chance.
Another cat on Purrs in Scotland had epilepsy and was put on phenabarbatone from the big animal hospital up there where he had an MRI, which is the standard drug for eplilepsy. Thats how I found out that when a cat had seizures and nothing showed on the MRI or other tests, epilepsy was diagnosed.
There are however other things that cause seizures and your vet must have seen something in the test results which is why Riley was called back.
I do hope that it is something that can be sorted and that the MRI comes up with something definate, they are wonderful things as long as there is someone qualified to read them and it sounds as if he is in exactly the right place.
I am thinking of you and Riley and sending all the best vibes for tomorrow
