What test was used to diagnose the EPM? I'm curious because many times things are diagnosed as EPM that are not EPM.
.How far downhill are they before treatment doesnt work? What % of recovered horses recover enough to be sound for work? How will I know when he is to far gone to keep attempting to treat him?
Its hard to find answers to these questions because they are very individual to the horse. My horse was actually falling down when he had it as a 4 year old, but he recovered and is now a good trail horses. Some horses don't get near as bad and never recover to riding soundness. As to % that recover - I really don't know. I believe I read somewhere that a medication for EPM is considered successful as long as 60 or 70% of the test horses improve 2 grade scales. I'm saying this off of memory - so I'm not 100% positive, but it was something like that.
As to when not to attempt treatment - again, that is very individual decision and no one should make you feel bad for either trying treatment or putting him down. Its extremely hard and I'm so sorry you are facing this right now. Originally I said I would not treat Toby again if he came down with it again, but when faced with a few symptoms I had worried might be it I was questioning that decision. I don't think I know what I will do again if I'm ever faced with it until it happens.
My vet did have my horse on a DMSO IV a couple times a day when he was first diagnosed and it seemed to help him for a bit afterwards and didn't impact the effectiveness of the medication. I don't know about a rub for the legs though.
You may want to look into giving a cup of corn oil after administering the meds (mix in a tasty feed) as it is believed the oil administered right after the ponazuril helps it be absorbed better.
Also look into therapeutic levels of vitamin E. I believe it was 18000 IU per day - but I would have to double check that number. Vitamin E helps with the nerve regeneration and helps through the recovery. Just make sure its pure Vitamin E and not mixed with selenium or something else that could be overdosed. Your vet should be able to get it for you.
Good luck to you and your horse. EPM is a hard and trying disease and again, I'm so sorry.