Now understand this, with EPM there is no result of just negative or positive, it is a percentage. According to my vet they don't usually get concerned until there is a result of around 85%. Because my horse was showing neurological signs I went ahead with treatment. I have only been treating her for a bout week now so I do not have any information on if the treatment is working yet.
But because of my recent issues with my mare I decided I would share this website that I found during my research, that has a lot of good information about EPM.
My mare is showing much improvement on the EPM medication, not only noticed by me and my family but was noticed by both my equine acupuncturist and my farrier.
My mare finished a 2 month course of medication and the vet said that should be enough, so far so good.