Diet for Megacolon cat.

My cat Buttons is having a lot of issues and nothing seems to be working. He was diagnosed with Hyperthyroidism last year, along with high blood pressure. He currently takes 6 rotations of Methamazol daily and it's helped quite a bit. He also has 0.10 CC's of meds daily for his high blood pressure. Since this last year and being diagnosed and given medication, he's now developed constipation problems. He was given 3 CC's of Lactulose a day to help out, but he'd still end up costipated. It's to the point where he can only manage to push out a ball or two and it's as hard as a rock. He takes Cisapride once a day and 6 CC's of Lactulose. I had him at the vet yesterday and he was so plugged up that he needed 2 enemas. He hasn't had a colon evacuation yet, but the vet mentioned that it might be time to talk about his future since he's coming in to get unplugged nearly every month. She also has him on an all fibre diet. His food has at least 3% fibre. And she upped his Lactulose to 9 CC's a day now.

I was reading online and now I'm coming across websites that are saying an all fibre diet is actually terrible for a cat who keeps getting constipated, or who has mega colon. And other websites and my vet is vouching for it. But clearly nothing is working for him. He still looks healthy. He still cuddles, eats, drinks, walks aorund and plays from time to time. He still bathes himself. He's about 16 years old.

Does anyone here have any advice for me? My vet seems to be out of ideas. Does anyone here have a Megacolon cat who went through something similar? Was there anything that helped? Anything I can do? I've even added pumpkin to his fibre food.

My kitty has occasional constipation issues due to IBD and I brought up to the vet about the fiber in the diet.  She told me that as long as they haven't gone into megacolon some extra fiber can help but once they have gone into megacolon getting as much fiber as possible out of the diet helps.  Since the high fiber isn't helping I think going the other way would be worth a try.  Some kitties also do better on Miralax than they do on the lactulose.  They both work by increasing water in the colon.  The Miralax is easier to give because it is a tasteless powder that can be mixed in wet food. 

Increasing water in the diet helps.  I don't know if you feed wet food but that would increase fluid intake as well as decreasing fiber.  Some kitties will drink more with a water fountain.  It didn't work with my kitty so it's kind of individual to the kitty.  Putting water bowls in several places around the house can also increase fluid intake.