Epileptic Cat - Sudden difficulty walking/jumping/moving

Hi all, any help much appreciated. We have a 10 year old epileptic cat, developed due to head trauma at an early age. He has been on Phenobarbital for around 5-6 years now with sporadic seizures occurring but none in the past 6-8 months. He is usually a very happy cat, runs around playing with toys, kneeding, purring. The past week he has taken a turn and has looked very weak and wobbling when walking, falling over, unable to jump low heights and unable to walk up stairs. He's eating/drinking fine and temperament seems okay. We've had his bloods checked, his legs and claws are all fine. One vet prescribed arthritis medication which has not made any difference - I find it hard to believe arthritis can set in so suddenly? We went to have him checked again today and vets are suggesting it could be a neurological problem as they can't find anything else, I guess meaning that his brain function has deteriorated to where he can't control his body? They didn't give many options in terms of treatment, can't get a brain scan as too expensive, seemed to just think we should see how he goes. Does anyone have any opinions on whether the diagnosis could be correct and if so any forms of treatment or even supplementation that could help in any ways?

Hello!  I'm sorry that your cat is having such a hard time.  The scenario that you describe is more common than you'd think; cats with brain disease / balance issues face a double-whammy when certain movements start to cause them pain.  If you or I had a muscle that caused pain at a certain point in our gait, then we would quickly develop a way to walk around it ie by limping.   However, if your cat was already compensating for balance issues and on top of that they have a pain to deal with, I would not be surprised if this were to throw their coping mechanisms severely.   Cats can usually mask / ignore pain to some extent; it has to be quite bad before they adapt their behaviour.  I can therefore well beleive that in this scenario, a cat might suddenly reach the point that they simply can't walk normally anymore, losing their coping mechanism for the brain injury seemingly overnight.  It is good that your vet was aware of this and thought to try pain releif; hopefully it was given a judicious trial, with suitably strong drugs before pain was ruled out.