KENNETT SQUARE, Pa. - Ever been mystified by your horse's sudden change in behavior, odd movements or appearance? It could be a neurological problem and there's an easy set of diagnostic tests you can do at home as Dr. Amy Johnson demonstrated at New Bolton Center's First Tuesday lecture Sept. 6.
Johnson - who is 39 but looks more like one of her young UPenn vet school students than the only veterinarian in the United States board-certified in both neurology and large animal internal medicine - titled her talk, "Neurological Exam: Evaluate Your Horse Before Someone Gets Hurt."
"I'm going to treat you like you were vet students," Johnson began. "I'm going to walk you through a neurological exam that I have done on some of our patients; that I do every day on somebody else's horse.
"I start by looking at the horse's behavior and their mental status," she said, introducing here two demo subjects as Mr. Fazo, a 7-year-old Standardbred gelding, and Mr. Red, a 6-year-old Tennessee walking horse gelding.
In doing these tests, she said, owners should take into account the horse's age, breed and experience. Her two subjects were calm and relatively used to being teaching horses.
"If one were a 2-year-old Thoroughbred colt in racing shape and I was standing here waving my arms, I would think there was something wrong [if it stood there quietly.]," she said.
"What they're doing now is normal for a teaching horse, not normal for a 2-year-old Thoroughbred," she said as she started to run her hands along Mr. Fazo's head, feeling and prodding.
She was showing how to assess the cranial nerves, the back part of the brainstem which controls important functions like heart rate and breathing.
The cranial nerves exam assesses the back part of their brain or brainstem which does a lot of important things such as controlling heart rate and breathing, said Johnson, who is assistant professor of large animal neurology and large animal internal medicine at New Bolton.
Johnson handles the two teaching horses easily and comfortably, reflecting not only her veterinary professionalism but her much longer experience with horses which began a few years after she decided she wanted to become a vet, at age 9.
But her passion for animals started at a much younger age when she was growing up in Pitman, New Jersey, caring for baby birds that fell out of their nests, hand feeding them and nursing them until they could fend for themselves.
Horses came at bit later into her life after she had managed to talk her dubious parents into letting her have riding lessons and a pony of her own which she bought for $500 with her own money in her early teens.
Thus her ease around Mr. Fazo as she assesses each of the 12 cranial nerves.
First is the olfactory nerve, which she says can be difficult to assess but if the horse has a healthy interest in food, she said as she gives Mr. Fazo a snack, it probably has a normal olfactory nerve. She runs through the list of nerves demonstrating quick and easy tests. She waves her hand in front of the eye to test the optic nerve, adding that you can also use a penlight to see if the pupil constricts. The oculomotor (eye movement), the trochlear (eyes), trigeminal (face and mouth chewing) . . . and so on down to the final and 12th cranial nerve.
This one, the hypoglossal, is her favorite, Johnson said as she eases her fingers into Mr. Fazo's mouth and pulls out his tongue which he immediately with withdraws. His reaction shows a normal response by his hypoglossal, the nerve Johnson said is most affected by two neurological diseases, EPM (equine protozoal myeloencephalitis) and Lyme disease.
Mr Fazo "clearly passes all those tests so he has normal function," said Johnson.
"So now bring Mr. Red over," she said nodding to an assistant, "I'll show you the cranial exam on our other horse - I'm going to give it away that he's our abnormal horse, but you're going to figure this out."
Johnson quickly goes through the cranial nerve tests which Mr. Red passes until she reaches the final test, the hypoglossal. She pulls his tongue which comes out without resistance and just hangs out even after she lets go. The audience groans in sympathy.
"Little different from the last horse, right?" said Johnson. "You can see he's letting me pull it out of his mouth and not working to retract it at all. This is what I would consider an abnormal response.
"As you can see, these are all things you can do at home with no special equipment. So far I've just used a penlight and a pen [to poke him]." said Johnson..
The next tests involve movement of the horse: "First is cervical reflex test - we tap along the neck and we should get a little bit of an ear twitch and sometimes the mouth as well."
She paused and turned to her audience: "If you think a horse is neurological I don't want you riding him."
Johnson asks an assistant to walk and jog the two horses.
"I'm looking to see that they have a regular footfall. So that walk is a four-beat gait and he's not doing anything abnormal like stepping on himself. That he's not swaying to one side or another that he's not dragging his toes in the ground. He should keep his feet underneath himself at all time."
She checks for balance and recovery by pulling their hind ends to one side to try to unbalance them as the horses walk. Fazo recovers easily, Red is more awkward.
"Assess his strength and recovery. Both sides. So, as you do this you should also take into account their personality and breed. He didn't fight me but he recovered very well.
"If he were a Thoroughbred he'd probably be in another zip code by now," said Johnson to laughs from the audience.
Johnson and the assistant lead the horses in tight circles "to pick up ataxia abnormalities in a horse. [Fazo's] doing it appropriately . . . even, not pivoting . . . Both ways. He clearly knows where his feet are, where the ground is."
Mr. Red, though, moves more awkwardly,
"As he's walking, watch his back legs. They're a bit slower to move and a little wigglier to move. Even at the walk you can see his back legs are not moving quite as predictably as the last one. To Mr. Red's credit he's a Tennessee walker so his stride length tends to be a little bit longer than a normal horse's. He's over-reaching just a little bit and that's an indication of mild spinal cord disease."
In the tight circles, Red "does that pretty well but occasionally he gets a little discombobulated."
Johnson's diagnosis for Red: "Pending a full neurological work up, EPM is very high on the diagnosis . . . towards the mild end of the spectrum."
But, Johnson added, his symptoms are enough that she doesn't feel anyone should ride him.
The two teaching horses are sent back to their pastures and Johnson takes questions from the audience.
Asked if EPM can go dormant, Johnson said, "We don't really know … The only way to definitely know if the parasite is still there is to look at the spinal cord when the horse isn't alive.
"Even if we could do an MRI of the whole horses, we couldn't see it. [The parasites] are too small. We have no technology to test if the parasite is totally dead or just in hiding.
Lyme disease could also have similar symptoms with more cranial involvement: "Lots of issues with swallowing, facial twitching and fewer issue with the spinal cord. But not every horse reads the book."
Asked about the reliability of lab tests for EPM and Lyme, Johnson said they were "very reliable at telling whether or not the horse has antibodies against the causative organism. But if I went out and tested every horse in this county about 60 percent would be positive for EPM or positive for EPM in the blood samples.
"However, if I examined spinal fluid and compared it to what's in the blood then it's pretty darn accurate within 90 percent on predicting whether a horse has EPM or doesn't," Johnson said, adding that doing both samples was much more reliable than just doing blood.
Asked about prevention, Johnson said keeping horses in a safe area may be impossible and keeping them from eating possum manure was difficult.
There is "no absolute way to prevent it in this area other than keeping food covered and things like that."