It does sound similar in part – no scratches and my guy only mildly stocks up in one leg (so far) and it goes down immediately after turn out. But WOW how mysterious as well…and depressing!
Wasn’t my horse, I can only report what I was told. But I’m pretty sure no one ever actually tested. Horse has been gone for years at this point.
My horse has been gone for over 20 years, my daughter was just a toddler when I let him go. She’s 28 now. We got lucky that my vet was lucky to be able to diagnose him off the belly tap. I miss that boy. I cried for a month waking up before deciding to let him go.
If not cancer, might be worth investigating ESPA/DSLD. Seen a few that the earliest symptom was a swollen sheath.
I don’t really have any great suggestions, just wanted to commiserate with you about horses with mystery symptoms. I went down the rabbit hole with one of mine many years ago - we never got a diagnosis.
I did want to say that if it’s EPM, I would think the treatment would be longer than 10 days. And he could have EPM along with something else. There may not be one smoking gun, but a couple of things masking each other.
You’ve done so much already - maybe a spinal tap would give you some answers, or at least rule it out. And not all horses recover fully from EPM. The neurological symptoms may be permanent.
I second putting him on senior feed, to see if he can gain weight on it.
10 days is appropriate for the dec/lev combination, then you assess from there