Ive dealt with a slew of EPM positive horses that had symptoms as mild as “stabby stride behind at the trot” or “feel like a green bean at 10 when carrying a rider” or “stumbles behind more often than the footing would indicate”… EPM, Ulcers, and Lyme all have such incredibly unique expressions in each horse, my vet team has found all 3 in animals (multiple times) that did not express the “normal” symptoms… Much like humans- every horse is an individual and illnesses manifest in different ways. Also, genetically being a prey animal- horses are hard wired NOT to show weakness, again- making signs of pain or discomfort manifest in explosive reactions or quiet behavioral changes- things that would not make them susceptible to being eaten… kudos to you for investigating, and also being willing to make the hard call if you cant find a reasonable explanation- horses bring us so much joy, and cause us so much pain all at the same time!
At this point, even if you do fix the underlying medical issue, I don’t think the horse will ever be safe to ride.
He has learned that bucking / bolting removes pressure. When he gets stressed, he will likely return to those coping skills.
I hope I’m wrong, but I have a similar story and this is the conclusion I reached. I bought a horse that put me in the dirt and broke my back 2 years ago. Then I came off a few weeks later and broke my thumb. I was terrified every time I climbed into the saddle.
I just spent 9 weeks in Texas working with a phenomenal trainer. He has been training horses for 20 years, traveled with very big name clinicians, and is a kind, ethical, responsible, thoughtful, and talented person. He got me and this horse to a place where I could walk, trot, canter both ways, work on collection, back up, serpentines, and ride with a flag. But I could always feel the tension simmering under W’s skin and I was never really comfortable. The trainer told me if I wanted to keep riding him after I took him home, go for it, but ride in a small area to contain him when he bolted. Not if, when.
I made the decision to never ride him again. Now he’s a retired pasture pet. There will come a day that I can’t afford a horse I can’t ride and I’ll be faced with a hard decision, but I know the hardest decision I had to make is done - I’m never putting myself at risk again with him.
I hope you find out what’s happening to your guy medically and I also hope that you decide to keep yourself safe from harm in the future. Keep us posted - this is really hard and it’s good to have a community who is with you in spirit!
To clarify… does this suggest that if the parasite has not crossed the blood/brain barrier, symptoms are more likely to be physical (stumbling, gait irregularities, etc.), but if we see behavioral changes, then it is more likely because the parasite is in the brain? Or does the presence of any symptom indicate that the parasite has crossed the blood/brain barrier?
If the former, does that imply anything about severity, treatability, prognosis, etc.?
Symptoms do not appear until the parasite crosses the blood/brain barrier. The symptoms experienced depend on where the parasite develops lesions. The difficulty in treating EPM is the medications have a hard time making it into the lesions (per my vet). The information below explains:
Once ingested, the sporocysts migrate from the intestinal tract into the bloodstream and cross the blood/brain barrier. There they begin to attack the horse’s central nervous system. The onset of the disease may be slow or sudden. If left undiagnosed and untreated, EPM can cause devastating and lasting neurological damage.
The clinical signs of EPM can be quite varied. Clinical signs are usually asymmetrical (not the same on both sides of the horse). Actual signs may depend on the severity and location of the lesions that develop in the brain, brain stem or spinal cord.
Also, most horses have a strong enough immune system to fight off the parasite. AAEP has some good information about EPM and treatment. What I found interesting is some horses may have had EPM for years before exhibiting symptoms. Your horse, and maybe mine, were infected before we bought them. Stress can weaken the immune system, resulting in an infection with symptoms.
Thank you!
Yep, my horse’s epm symptoms were extreme irritability and trying to bite when curried on the left side, but not the right. No typical neurological symptoms at all. She also had to be treated for both hind gut and fore gut ulcers. This horse is never stalled ND is on pasture! I did read an article from a vet hospital in FL that theorized that Epm could effect the nerves controlling the digestive tract, causing ulcers. They explained it but it was well over my head!
@RedWingedBlackBird I didn’t read through all the responses, so I apologize if I missed details or this was mentioned…but this sounds very much like EDM.
That’s how my horse first started to present…explosive behavior and got more dangerous on the ground. And my guy had always been sweet and easy and kind. He became anxious and unpredictable and prone to random explosions under saddle (later in the paddock while just grazing).
They don’t always look really neurologic…mine didn’t show neuro signs until right before we euthanized him. Mine ended up having lesions in his brainstem on both sides…along with a host of other lesions.
There are some really good videos out there from Dr. Amy Johnson and from Dr. Amy Polkes about EDM.
An unhappy update: After a thorough workup at the vet hospital, we have euthanized my gelding.
He saw internal medicine, neurology, ophthalmology, and orthopedics. Initially, the doctors thought there was an issue with his vision, particularly on the right side (which was the same side that I and others at the barn had had a feeling about). The examination, including ERG, revealed mild cataracts, but nothing that should cause his level of reactivity. He had some mild arthritic changes along his back and neck, but nothing particularly unusual. They did not see any obvious neurological signs related to balance, gait, knowing where his feet are, etc. Fortunately (?), he had one episode while there and spooked quite badly at a vet student who wasn’t doing much of anything at all, so the doctors were able to see it firsthand.
Their best guess, albeit without a ton of confidence, is EDM. They think the vision issues may actually be processing issues as opposed to an issue with the eye. They also said that many of the things we’ve observed-- e.g., reluctance to go into his stall (light to dark)-- are associated with EDM. He was a very sweet, kind horse when he was himself, and they did not think that his issues were behavioral. They said-- and I agree-- that it seems like a cognitive thing where he was incorrectly processing stimuli around him. So if not EDM, then they think it was something else going on in the brain. We’re doing a necropsy, but she cautioned that even if it is EDM, we may not see anything in the results.
I wish that I had a diagnosis with clear test results to back it up, but I suppose that I got what I wanted, which was the ability to come to make a clear choice. He is at peace now and I am happy for that.
Thank you to all for the advice and support and commiseration.
So so sorry:(
EDM is the most heartbreaking disease I’ve experienced with any of my horses and I wouldn’t wish it on anyone. It’s so hard not to have a definitive way to diagnosis…and it can be so variable in the presentation. Hugs to you…waiting for the patho report was probably the most agonizing few weeks I’ve ever experienced. I was lucky in that I did get closure with my guy’s necropsy report…it was bad and he had other organs that were also impacted. It let me have peace about making that final decision…so for that I am grateful.
This was a well written article from Lauren that sums it up well…https://www.chronofhorse.com/article/have-empathy-in-the-face-of-the-hardest-choice/
I am so sorry, but it sounds like you did everything you could for him. Even if the necropsy does not show any clear answers, I think you made the right decision for him and he is at peace now. Hugs to you.
I am so sorry. You did the right thing for this poor horse as hard as I’m sure it was.
I’m so sorry you had to say goodbye. You did the right thing for him although it’s one of the hardest for us.
((((hugs))))
I’m so sorry, my heart goes out. You made the right call 
So sorry to hear that you lost your boy. My heart breaks for you. {{{Hugs}}}
I’m so sorry @RedWingedBlackBird. But it sounds like he was lucky to have a caring owner like you at the end to make the right decision. 
That is a sad update. I am sorry.
Oh so sorry. 
I am so sorry. I know it’s not the answer you wanted.
But I am so glad you pursued the diagnosis and you came to the decision. I hope the necropsy gives you some closure as well.
I absolutely think you did the right-but-never-easy thing by your poor horse. Please be kind to yourself and allow yourself to recover and grieve.
I’m so sorry for your loss. May he, and you, finally be at peace.
