Hi MW, welcome. I'm very sorry to hear of your diagnosis. If it were me, I'd definitely go with a therapeutic ketogenic diet, although I'm not that well versed on all the sciencey details. It sounds like you already know what would happen on a low-fat diet. That's been the unfortunate experience of a lot of us here!

I wouldn't be doing it vegetarian - in fact, I'd probably go full carnivore because there's so much that can be neurotoxic in plant foods, but if that's your ethical decision, there are ways to do it.

Amy Berger wrote a book called The Alzheimers Antidote, focusing on ketogenic nutrition for that disease. I haven't read it (I hope I don't ever have to), but I think there's a lot of crossover when it comes to different brain/neurological conditions and diet.

Dr David Perlmutter might be someone you want to look up. I believe he's a neurologist. Here's a short video he did about a study on a few Parkinson's patients. He wrote a book called Grain Brain, which I also have not read. I'm a terrible reader.

DietDoctor.com, as for just about all topics related to low carb nutrition, is an excellent resource. They even have vegetarian ketogenic meal plans and recipes.

Maybe someone with more background will chime in here, but I hope that helps a bit. Best of luck to you.