Sidewinders or EPM? How about both

I'd like to start this blog by thanking the Blogosphere and all the other bloggers out there who wrote about their troubles with EPM. Your blogs got me through the long nights of frantic and weary searching for answers and resources. You all know what it's like to have a heart horse who is suffering, and you know how hard it is to get answers fast.

Your journeys helped me along mine, and this blog is my "pay it forward."

This is Blue.

We have been life partners for about 20 years. That makes us both pretty old. He's 28 years old, and up until about 8 months ago, he was doing just fine with exactly no intervention whatsoever. In fact, my husband would joke that he'd be saving for retirement, but he has to pay board on Blue for another 20 years.
But in November 2015, Blue went out in the field in the morning with no trouble and by dinnertime he was walking sideways.
We gave him some bute and let him rest in his stall. He had started to stand oddly as well, with his right hind leg "kicked out" in an awkward resting position. He didn't seem to be in any pain, and he was still eating plenty and drinking, and he loves my children (ages 10 and 2) and would nicker to them for his treats.
We called the vet and got the diagnosis of "Sidewinders." As it was described to me initially, Sidewinders is a rare neurological disorder mostly found in elderly horses with a prevalence in geldings.
Not much you can do, but the hind end weakness was remedied with some steroid shots to strengthen him up. And it pretty much worked. He was "crooked" but not "tilted" if that makes sense. We would put him in the arena with his much younger buddy and they would run and buck. He loved to roll, and would get up and down with no problem.
Since he's totally retired except for the occasional pony ride, I was thrilled with this progress.
Just before Easter, my daughter even took him out for some "low speed" fun bareback.

Just a week later, he was back to "crab walking." His occasional crookedness turned into a full tilt, and he looked as though a stiff wind could knock him right over.

Something had to be done, and I was no longer satisfied with the "not much we can do" treatment plan.