Equine Vet www.modernequinevet.com
Vol 7 Issue 5 2017
Designing a Program for Young Horses
Making Anesthesia Safer Stress Relief? Stop and Smell the Lavender Rider, Horse Experience Prevents Injury Technician Update: Temporohyoid Osteoarthropathy
Table of Contents
Designing a Deworming
4 Program for Young Horses Cover photo: Shutterstock/Alesya Selifanova
Serum Antibody Titers Might Not Be Best Test for Lepto Uveitis in UK................... 3 Surgery
Making Anesthesia Safer............................................................................................................. 7 technician update
Case Study: Temporohyoid Osteoarthropathy..................................................................12 News
Know the Signs of EPM—A Master of Disguise....................................... 9 Rider and Horse Experience Important to Risk in National Hunt Flat Racing .......................................................................10 Stop and Smell the Lavender .................................................................10
advertisers Shanks Veterinary Equipment...............................3
Contact Matt Todd to advertise today.
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Serum Antibody Titers Might Not Be Best for Lepto Uveitis Diagnosis in UK Uveitis (left) is a common cause of ocular pain and blindness. Courtesy of the Equine Veterinary Journal
Leptospira have been implicated as a cause of equine recurrent uveitis in mainland Europe and the United States, but U.K. researchers found that it was not a significant cause of the condition in horses in the United Kingdom. Or at least they found a lack of Leptospira positive serum antibody titers, so it appears to be pretty low, according to a recent study out of the University of Liverpool in Neston. “Exposure to Leptospira spp. is common in horses, but serum antibody titers do not correlate well with ocular signs,” the researchers wrote. Because of this, the researchers found that serum antibody levels were not helpful in differentiating Leptospira-associated cases from other causes and suggested to veterinarians that testing of aqueous humor was required to confirm involvement of Leptospira in recurrent uveitis cases. The researchers did a histological examination of 30 eyes enucleated from recurrent uveitis cases and 45 eyes from control cases to look for signs of uveitis, a common cause of ocular pain and blindness. Blood and aqueous humor from all eyes were also tested for Leptospira antibody levels using a microagglutination test. All eyes from the uveitis group showed evidence of the condition, such as lymphocytic inflammation of choroid and ciliary body, uveal hemorrhage and retinal detachment. There was no evidence of disease in the control group. Just more than half of horses (65% uveitis cases and 41% controls) were serologically positive for Leptospira, the most commonly detected serovars being bratislava, autumnalis, copenhageni and australis. There was no significant difference in serum antibody titers between the groups. Six eyes (8%) had detectable Leptospira antibodies in the aqueous humor—all recurrent uveitis cases—meaning that a positive antibody titer in aqueous humor was significantly associated with equine recurrent uveitis, the researchers explained. When these cases were compared with recurrent cases without positive antibody titers in aqueous hu-
mor, there was no significant difference in serum antibody titers, suggesting serum antibody levels may not be helpful in differentiating Leptospira-associated equine recurrent uveitis from other initiating causes, according to the researchers. MeV
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For more information: Malalana F, Blundell FRJ, Pinchbeck GL, McGowan CM. The role of Leptospira spp. in horses affected with recurrent uveitis in the UK. Equine Vet J 2017 Apr 24 (Epub ahead of print). http://onlinelibrary.wiley.com/doi/10.1111/evj.12683/full
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Deworming Program Practice ESP when helping owners to develop a deworming program for their young horses, suggested Wendy Vaala, VMD, DACVIM-LA, to slow the development of resistance for cyathostomins and ascarids, two parasites of concern in this age group. This isnâ€™t extrasensory perception, but rather a tailored program that is effective, sustainable and selective, and includes a total parasite control program, Dr. Vaala explained at the annual meeting of the American Association of Equine Practitioners in Orlando, Fla. An effective plan incorporates fecal egg count reduction tests to make sure recommended dewormers are still working. Being sustainable means offering a program that makes financial sense in terms of manpower and costs to the owner. â€œOffering the $50 fecal on every horse every year can become cost-prohibitive for large farms and does not focus on testing the horses at highest risk for parasites. Some horses may need more than one fecal per year. When testing
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the efficacy of a specific drug class, it is imperative to perform a fecal egg count reduction test (FECRT) that requires collection of a pretreatment fecal and then a posttreatment FECRT 10 to 14 days later. A single fecal analysis will not help decide if the dewormers being used are still effective. Farms must see a return on investment. For example, a FECRT can be offered on a representative group of foals or weanlings rather than on all foals and/or weanlings on the farm,” she said. Be selective and target the correct parasite and the correct stage of its life-cycle. “It needs to be selective in terms of customizing the program for the farm and not assuming just because two breeding farms are in the same county, they necessarily have the same drug-resistance problem,” Dr. Vaala said. For good parasite control, provide a deworming protocol as well as a husbandry program that encourages owners to manage the environment in addition to just administering anthelmintics. The most concerning parasites prior to weaning are ascarids, and between weaning and yearling, focus in on cyathostomins. In some
areas, tapeworms are also a problem for this age group, she suggested. “No new drugs have come along [for this age group], so for the few drugs that are out there, I encourage you to know something about their different modes of action and spectrum of activity. Sometimes that will dictate which drugs you choose,” she said. She suggested that the veterinarian offers to give the farm a “physical.” This should be a chargeable service. Going over the farm can give some insight about any environmental controls that are in place and others that the veterinarian could suggest to decrease parasite exposure. “Look at risk assessment, get their drug use history on the farm, and start to offer some changes in management,” she said. “I think the other goal is ‘do more with less’. “Usually, an overall objective when you set foot on a breeding farm is to get the same or better parasite control results with decreasing drug frequency,” Dr. Vaala said. Consider the likely stage of the parasite that is being targeted and choose a product that attacks that life stage. If there are a large number of coughing, snotty-nosed
foals, one would probably want to target ascarid larvae in the lungs, rather than adults in the GI tract, for instance, Dr. Vaala suggested. That requires a larvicidal drug, not just an adulticide. In the first couple of days of an ascarid’s life cycle, the larvae migrate through the liver to the lungs. They spend two to three weeks randomly migrating through the lungs, causing inflammation, lowgrade fever and cough. They are then coughed up, swallowed and continue their development to adults in the small intestine. In the intestine, there is a prepatent period of 10 to 15 weeks, after which time infected horses begin to shed eggs on the pasture. “Nothing kills those ascarid eggs,” she said. “You can have resident ascarid eggs persist and over-winter on the pasture anywhere from five to 10 years.” Tapeworms have an indirect cycle; once the eggs are passed, they need to be ingested by a mite, where they develop for several months. The horse digests the mite, and then they take two to four months to become egg-laying adults. “Most of our fecals will underestimate tapeworm eggs.
for Young Horses
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ESP Against Parasites Effective Sustainable and selective Parasite control The Farm Physical You can throw a lot of drugs at horses for parasites, and it won’t fix the problem unless the owner also manages the environment. A farm physical enables a veterinarian to evaluate the farm and its practices to develop an individualized deworming program. It should be done yearly.
Here are things to consider: • The dewormers they are using, and how often they are given • Age range of the herd • Stocking density • Whether the herd is open or closed • Evaluate the farm’s biosecurity program • Perform fecal tests to assess control
Recommend environmental controls: • Mowing the pasture three times a year, which decreases strongyle eggs by exposing them to sunlight • Taking animals off the pasture when harvesting hay, rotation and harrowing. Do it during a hot, dry time of year, • Remove the manure weekly • Compost • Cross graze with another species.
However, constant method with centrifugation might give you the chance of seeing them if they are there,” she suggested. Luckily, foal diarrhea due to Strongyloides westerli has lessened with modern deworming programs and products. “It usually takes a tremendous number of strongyloides eggs to cause disease,” she said. “You will find that if you ask the right questions, many farms which insist on deworming their foals at 2 to 4 weeks of age usually live in fear of strongyloides, but it was a problem in the past.” If they are reluctant to stop deworming so early, offer to take fecals on young, 2-to 4-week-old foals to convince them that this age group is not shedding, and they do not have a strongyloides problem, she suggested. Use fecals selectively, but have a goal in mind when performing a FECRT and provide guidance for collecting samples and the assay to use to assure that the best information is available. Use the results as an opportunity to educate owners about the importance of preserving dewormers against the development of resistance. Unfortunately, owners are still doing rotational deworming, she said, often hearing “I wasn’t sure what dewormer to use, but you’ll be happy to know I used all of them last year,” she said. All too frequently, veterinarians do not become involved until there is an ascarid impaction. Horse owners are surprised and of-
to download a patient handout on deworming 6
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ten ask: “‘How can that possibly happen on my farm because I’ve been deworming my foals every 45 days?’ Therein lies part of the problem—way-too-frequent use of drugs, and often the wrong drug at the wrong time,” she said. Try to get owners to allow you to intervene before having to deal with a colicky foal with an ascarid impaction, she suggested. Resistance is becoming a serious problem, and veterinarians must educate owners about the best ways to delay the onset of drug resistance, she said: • Delay the time of the first deworming until foals are at least 60 days of age. • Use the longest deworming interval possible in the foal, preferably 8 to 10 weeks. • Don’t rely on one drug class, but be strategic when selecting which drug class to recommend. “If it is an open herd, consider adding larvicidal treatments to those mares and foals returning from other breeding farms since they may be harboring prepatent, drug resistant parasites,” she suggested. Although many veterinarians are trying to educate their clients, surveys in the United States and the United Kingdom show that veterinarians are not getting the message across. Owners continue to overtreat their animals with chemical dewormers. “The take home message [from the surveys] is that the traditional rotational deworming protocol is still alive and well despite evidence-based medicine that suggests a better and more selective strategy is available,” Dr. Vaala said. “Keep it simple, but include that farm physical as part of your offerings,” she suggested, “and be patient. Tradition has been out there a long time. Choose patience, wisdom and baby steps, but start with the first year of MeV life.”
Anesthesia Safer B
Because recovery from an-
esthesia is such a dangerous time for horses, even small differences among anesthetics could make a big difference to the animal, according to Alonso Guedes, MV, MS, PhD, DACVAA, who is associate professor of Veterinary Anesthesia and Pain Medicine, Veterinary Clinical Sciences Department of the College of Veterinary Medicine, University of Minnesota. â€œHorses can be disoriented, agitated and uncoordinated during re-
covery from anesthesia,â€? Dr. Guedes told The Modern Equine Vet, which makes recovery from anesthesia one of the most critical, but least controllable periods of a surgical procedure in the horse. Many sustain life-threatening injuries during that period. Dr. Guedes and his colleagues sought to determine whether a newer sedative, dexmedetomidine, would provide a better quality recovery than an older sedative, xylazine. They found that dexme-
detomidine was comparable with xylazine in horses recovering from sevoflurane anesthesia, but that it may be advantageous over xylazine in some specific situations. Six research horses were anesthetized for one hour on two separate occasions. On each occasion, the horse was treated with one of the two sedatives just prior to the anesthesia recovery phase. The horses were geldingsâ€”five Thoroughbreds and one Westphalian between the ages of 11 and 24. All
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Photo courtesy of Dr. Alonso Guedes
A horse in the recumbency position on a thick, rubberized pad, waiting to wake up.
of the horses were clinically healthy. After about 50 minutes under anesthesia, the researchers prepared the animal for rcovery—they catheterized and emptied the bladder, secured the endotracheal tube to the mandible, removed the monitoring equipment, secured a padded helmet on his head and transferred the horse to a padded recovery stall. They placed the horse in the recumbency position he was in during anesthesia. The recovery would be unassisted, so the stall had thick, rubberized flooring. Oxygen supplementation and respiratory support were provided during recovery from anesthesia. The endotracheal tube was removed within 10 minutes of the horse standing. There were no complications and all of the horses recovered from anesthesia without incident. “There were small differences in favor of the newer sedative, but overall these differences were not statistically significant,” said Dr. Guedes. For instance, the horses in the dexmedetomidine group moved a limb and tried to lift their heads a couple minutes sooner and there were fewer issues like head bangs. Most of the horses
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Tips for Helping Horses Through Recovery: Minimize flight-triggering stimuli. Maintain homeostasis. Talk to the horse during recovery. were recumbent for less time and made their first attempt to stand sooner on xylazine than dexmedetomidine, but none of the differences were significant. Although the data supported the use of either sedative, “dexmedetomidine may be advantageous in situations where even a small improvement in recovery quality is
clinically relevant and desirable. For example, the overall less head bangs with dexmedetomidine than with xylazine could be highly relevant to horses recovering from anesthesia for ophthalmic procedures, even though the difference was not statistically significant,” he explained. Dr. Guedes offered several tips for helping horses through recovery: 1. Minimize flight-triggering stimuli; 2. Maintain homeostasis and 3. Talk to the horse during recovery. “Horses are flighty animals and we won’t be able to change that. But we can minimize stimuli that would trigger a flight response in an awake horse,” he said. “Things like pain and sudden stimuli like startling sounds for example—maladaptive pain should be controlled and loud sounds avoided.” In addition, he suggested that veterinary anesthesiologists think of anesthesia as a continuum “with every phase potentially affecting the next. Horses that are in pain excited and stressed before anesthesia, that have poor homeostasis during anesthesia, will likely have an unfavorable recovery from anesthesia. Being proactive in correcting these problems is essential.” On talking to the horse during recovery, it may be helpful to remember that, as herd animals, horses rely on those around them— including humans in the case of the domestic horse—to keep them safe from danger. Emerging from pharmacologically induced sleep is not a familiar thing to most horses, and as such, could trigger a flight response. Talking to the horse in a calm, relaxed and confident manner during this period might enable the horse to connect to something familiar— the human voice and presence— and the experience may not seem so MeV strange and threatening.”
Know the Signs of EPM–A Master of Disguise More than 50% of all horses in the United States—and in some areas as high as 90%—have been exposed to equine protozoal myeloencephalitis. Most horses exposed to EPM will not develop clinical disease, but horses under stress are more likely to show signs, explained Sarah Reuss, VMD, DACVIM, Merial Veterinary Services. In some cases, horses may have an asymptomatic infection or not show signs for some time after becoming infected. Its ability to masquerade as other health issues makes it difficult to diagnose. Left untreated, it may lead to permanent damage. Dr. Reuss emphasized the importance of early detection. “These are the keys to stopping the progression of the disease. The faster treatment begins, the better the chance for the horse to recover.”
When it’s EPM, Be Ready
Ponazuril (Marquis, Merial) antiprotozoal oral paste is the first FDA-approved treatment for EPM. It crosses the blood-brain barrier to reach the CNS, killing the Sarcocystis neurona parasite. If treated quickly and properly, many horses can recover from EPM, according to a report from the American Association of Equine Practitioners. Veterinarians frequently use a loading dose to enable the ponazuril to reach a steady state more quickly. S. neurona is found in the opossum after it ingests contaminated tissue from intermediate hosts, such as the armadillo, skunk or raccoon. In its infective stage, the sporocysts are passed through the opossum’s feces, which the horse comes into contact with as it grazes, eats or drinks contaminated feed or water. Once consumed, the sporocysts travel from the intestine into the bloodstream and cross the blood-brain barrier where they can cause inflammation and damage the CNS. “EPM can evolve slowly or present suddenly with varied signs from mild to severe,” Dr. Reuss said. There are several factors that can determine its progression and severity, including: • How long the horse has been infected, • The points in the brain or spinal cord where the sporocysts have infected, • Stressful events during EPM infection. “Lesions, inflammation and pressure may develop in the brain, brain stem or spinal cord,” Dr. Reuss said.
“Depending on the location, they can affect how the disease presents itself and can make it tricky to diagnose.” Watch for these signs, noted by the AAEP: • Incoordination, weakness, abnormal gait, • Muscle loss on one side, usually along the top line or the hindquarters, • Paralysis of muscles of the eyes, face or mouth, evident by drooping eyes, ears or lips, • Loss of sensation of the face, • Difficulty swallowing, and • Head tilt with poor balance; horse may assume a splay-footed stand or lean against stall walls for support. She also noted that loss of coordination of the mouth, tongue and throat area may make picking up feed, chewing and swallowing it difficult, which can affect the choice of treatments. EPM also can be caused by a second organism, Neospora hughesi, but the life cycle is not well understood. Merial is now part of Boehringer Ingelheim. MeV Learn more about EPM and Marquis at http://marquis.merial.com.
For more information: American Association of Equine Practitioners. Horse Health, EPM: Understanding this Debilitating Disease. Available at: https://aaep.org/horsehealth/epm-understanding-debilitating-disease ModernEquineVet.com | Issue 5/2017
Photo courtesy of the Equine Veterinary Journal
Experience of Horse and Jockey Affect Injury Rate Among National Hunt Flat Racers Less-experienced jockeys and racehorses are more likely to receive fatal injuries, according to a recent study. The researchers studied 40,770 race starts to evaluate veterinary events and fatalities in all National Hunt flat races in the United Kingdom. They found that the incidence of fatalities in National Hunt flat races is 2.9 per 1,000 race starts. A veterinary event represented any injury or cause for the horse to be examined and/or treated by an oncourse veterinary surgeon. In total, 530 veterinary events were recorded, i.e. 13 per 1,000 starts. Fractures were the most common event, representing 23.5% of veterinary events and an incidence of 3.1 per 1,000 starts. Most (67%) involved the distal limb. Tendon and ligament injuries were the next most common event (16.4% or 2.2 per 1,000 starts), with the superficial digital flexor tendon being the most commonly injured structure. In 59 veterinary events, gait abnormalities (lameness or stiffness) were recorded.
The incidence of cardiovascular problems was 0.5 per 1,000 starts. Of these, vascular catastrophe accounted for 66%. The majority of respiratory events were epistaxis. Most of the 63 metabolic events related to heat exhaustion or fatigue. A fatal outcome was recorded in 117 (21.5%) veterinary events, giving an incidence of 2.9 per 1,000 starts. Most of these were due to bony injuries, which most commonly occurred in metacarpal III or metatarsal III. Nine tendon or ligament injuries described were fatal. All fatal cardiovascular events were due to vascular catastrophe. Races restricted to conditional jockeys were more likely to have a fatality and the odds of death were higher in horses in their first race compared with those which had run before, the researchers found. MeV
For more information: Allen SE, Rosanowski SM, Stirk AJ, Verheyen KLP. Description of veterinary events and risk factors for fatality in National Hunt flat racing Thoroughbreds in Great Britain (2000â€“2013). Equine Vet J. 2017 Apr 4 (Epub ahead of print).
Stop, and Smell the Lavender A recent study suggests that aromatherapy can help horses de-stress. Since inhaling certain scents may reduce stress in humans, researchers wanted to know whether aromatherapy could be helpful in veterinary medicine. Transporting competition horses from one location to another is stressful to the animals. The loud noises and confined spaces of a horse trailer and unfamiliar territory of a new venue may cause an increase in heart rate and levels of the stress hormone cortisol. This stress may provoke unpredictable behaviors such as running and an unwillingness to perform. Stress reduction therapies are highly regulated among competition horses, which often rules out the use of sedatives and herbal treatments. Kylie Heitman, a student at Albion College in Michigan, observed eight horses across two trips in horse trailers. Dur10
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ing each trip, the horses were individually hauled for 15 minutes. In one trial, the animals were exposed to an air diffusion of lavender oil during transport. In the other, the horses received a diffusion of distilled water. Ms. Heitman measured heart rate and blood cortisol levels before and after each animal's hauling. She found that cortisol levels were significantly lower when the horses were exposed to lavender. She also found a small, yet-not-statistically-significant decrease in the post-transport heart rate when the horses were exposed to lavender. The horses' heart rate increased slightly after spending time in the trailer without aromatherapy. These results warrant more study into lavender as another means for stress reduction in competition horses. She reported her results at the American Physiological Society (APS) annual meeting at Experimental Biology 2017 in Chicago. MeV
AAEV T M E M b E r s h i p Membership in the AAEVT is open to all veterinary technicians, assistants, support staff and those employed in the veterinary health care industry worldwide. Student membership is open to those currently enrolled in an AVMA/CVMA accredited veterinary technology program.
AAEVT Membership • • • • • • • • • • •
Bi-Annual Newsletter Weekly “HoofBeats” Email Newsblast Full access to www.aaevt.org, including the Career Center and the Library Up-to-date information on the AAEVT Discounted registration for AAEVT Regional Meetings and the annual AAEP/AAEVT Convention NTRA, Working Advantage and Platinum Performance Benefits The opportunity to participate in the AAEVT Online Certification Program or to become a member of the AEVNT Academy-Specialty in Equine Veterinary Nursing Scholarship opportunities. AAEVT’s Equine Manual for Veterinary Technicians (Blackwell Publishing 20% discount on purchase price) Opportunity to attend Purina’s Annual Equine Veterinary Technician Conference - All Expenses paid!
AAEVT Objectives • • • •
Provide opportunities for CE, training, communication, and networking Educate the equine veterinary community and the public about our profession Inform Members of issues affecting our profession Assist in providing the best medical care to improve the health and welfare of the horse
AAEVT Online Equine Certification Program
• A three course, 10 module, equine-only online program offered through ACT • Geared toward Credentialed Veterinary Technicians, Assistants, Support staff, & Students • Areas of study include: equine medical terminology, anatomy and physiology, parasitology, laboratory, diagnostics, equine basics (breeds, wellness, husbandry,) diagnostic procedures, emergency medicine, restraint, pharmacology, surgical assistance and anesthesia, equine office procedures • A certificate of completion is awarded to those who: Successfully complete required courses Complete the list of required skills (per a supervising DVM who is an AAEP member) Attend an AAEVT regional CE symposium and participate in the we labs • Those individuals who successfully complete the programs will be recognized as AAEVT Certified Equine Veterinary Technicians / AAEVT Certified Equine Veterinary Assistants depending on their current designation. The certificate is recognized by the AAEVT and the AAEP but does not grant the credentialed status by the AVMA • For more information go to www.aaevt.4act.com or call 800-357-3182
AAEVT Mission Statement: To promote the health and welfare of the horse through the education and professional enrichment of the equine veterinary technician and assistant.
Fo r m o re i n f o r m a t ion v ist w w w.a ae vt.or g
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*American Association of Equine Veterinary Technicians and Assistants
Case Study: Temporohyoid Osteoarthropathy Shana Lemmenes, CVT, VTS-EVN
all of the major differentials. These included equine protozoal myeloencephalitis (EPM), Lyme disease, parasitic migration and equine herpesvirus (EHV). As we ruled out the various disease processes, the corresponding medications were discontinued.
Photos courtesy of Shana Lemmenes
A 20-year-old Quarter horse gelding presented to the University of Minnesota Equine Center on Initial treatment included: May 31, 2014. He had IV fluids: lactated Ringerâ€™s solution (DMSO was added been ridden early that morning and seemed fine. He to the fluids every 12 hours for the first 72.) was found in his stall showing signs of ataxia (priAntibiotics: oxytetracycline IV every 12 hours, which marily in the hind limbs) later that morning. When was discontinued on June 5; trimethoprim sulfonamide they found him, the owners called the primary vetevery 12 hours (discontinued on June 18); IV penicillin G erinarian. She administered IV flunixin meglumine potassium (KPen) every 6 hours (discontinued June 23); and referred him to us for further diagnostics. IV gentamicin IV every 24 hours (discontinued June 23); Upon arrival, he was severely ataxic. He also had Eye medications: triple antibiotic ointment in the left muscle fasciculations, tremors, horizontal nystagmus eye every 6 hours and in the right eye every 12 hours; and multiple abrasions that had been sustained during atropine ointment in the left eye every 24 hours (rethe trailer ride to our clinic. He was able to stand on his duced to every 48 hours on June 24); antiprotozoalown, but our doctors gave his ataxia a grade 4. Later that ponazuril (EPM treatment) once-a-day. The dose was afternoon in the stall, his muscle fasciculations had readjusted once and then discontinued on June 5. solved but he would only move back and forth between Parasiticide: Oral fenbendazole once-a-day for three his hay and water with a minor pivot. He was very hesidays; tant to move his hind legs. Steroid: IV dexamethasone once a day. The dose was adOur neurologic evaluation showed an intact menace justed several times during treatment: response, horizontal nystagmus Anti-inflammatory: IV flupresent bilaterally and quite ofnixin meglumine every 12 ten with a corresponding eye hours (discontinued June 8, and ear twitch. I immediately but reintroduced post-op every 12 hours for three doses); drew blood for packed cell volGastroprotectant: omepraume (PCV), total protein (TP), zole once daily: complete blood count (CBC) Anti-oxidant: Elevate (vitaand chemistry panels. His PCV min E) once daily; vitamin C was 30% and his TP was 7 g/ (diluted in IV fluids) once daidL, which were within normal ly (discontinued June 5); vitalimits. The CBC showed a min B-thiamine IV (diluted mild elevation in white blood in IV fluids) at 2,000 mg once cells (likely caused by the stress daily (discontinued June 5) of illness and transport). His Antiviral: oral valacyclovir chemistry showed an elevation every 8 hours (reduced to in creatinine kinase, a muscleevery 12 hours on June 3, disspecific enzyme, which was atcontinued the next day). tributed to his falls in the trailer en route to the clinic. A mild Testing done dehydration was also noted on During his stay, the following the initial blood work. tests were performed to elimiDue to the fact that his nate differentials: symptoms could have been Cerebrospinal fluid analycaused by a multiple of sis was performed on June 1. things, we initially comA CT scan revealed thickening of the top portion of both stylohyoid bones. The levels of protein, creatimenced with therapy to treat 12
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nine, and glucose were all within normal limits. The CSF also showed he was negative for EPM (therapy for EPM was continued until the diagnosis of THO was obtained). Skull radiographs were taken on June 2, which showed no obvious sign of temporohyoid osteoarthropathy (THO); however, the radiographs were not of diagnostic quality due to the depth of his skull and the necessary use of the portable machine in his isolation stall. He was negative for EHV-1 infection (tested nasal swab and whole blood). Fluorescein dye staining, which was to assess if he received a corneal laceration during his falls in the trailer (at the time of the test there were no ulcers present; however, after surgery, a corneal ulcer was noted in the left eye and treatment was initiated). A Shirmer Tear Test was performed to check for abnormal lacrimation (this can be seen with THO); he had normal values bilaterally. A CT scan was performed on June 10 under general anesthesia. The images revealed thickening of the top portion of both stylohyoid bones with fusion of the temporal bones to the stylohyoid bones bilaterally. No other factors were observed and the brain was considered normal. He recovered from anesthesia without complication. Once our doctors were able to definitively diagnose THO, the owners were consulted and they elected to proceed with surgery. During this procedure, an incision was made parallel to the mandible just lateral of midline on the right side of the skull. The ceratohyoid bones were identified and compared with the CT, and then the muscles/tissues were bluntly dissected away from the ceratohyoid. The periosteum was elevated from the bone and the joint was dis-articulated. After the bone was removed, the area was flushed with ster-
ile saline and the incision was closed. Due to the length of the procedure and concern about his ability to recover from anesthesia—combined with a slightly unusual anatomy—only the right ceratohyoid bone was removed and the left side was left intact. During recovery from anesthesia, he obtained a self-inflicted corneal ulcer. Otherwise, he recovered well and continued to show improvement in his motor function as well as a decrease in neurologic signs, as swelling in the area decreased. His successful post-surgery recovery made him a good candidate for continued home care with regular veterinary rechecks to monitor his recovery. He was discharged on June 25 with instructions that the owners monitor for neurologic signs (head tilt, incoordination, circling, weakness, difficulty swallowing, or head shaking). He was sent home with oral TMS to be given every 12 hours for seven days. They were also instructed to apply a one-quarter inch strip of triple antibiotic ointment to his left eye every 6 hours and his right eye every 12 hours for seven days. They were asked to phone our veterinarians on June 27 about his progress at home and instructed to have his primary veterinarian remove the staples along his incision site no earlier than July 1. He continues to do well at home and has not had any further neurologic symptoms. MeV
Prior to working with this case, I had little knowledge of temporohyoid osteoarthropathy (THO), which is a disorder of the hyoid apparatus (also known as the voice box) and surrounding structures. The hyoid apparatus and larynx are suspended from the skull via the temporohyoid joint (THJ), which is located in the temporal region of the horse’s head. THO is a bony growth of the tympanic bulla, proximal stylohyoid, and petrous temporal bones. This results in fusion of the temporohyoid joint—and in some cases—fracture of the small bones that make up the hyoid apparatus. Although the cause is unknown, horses with THO often display neurologic signs including vestibular deficits like a head tilt and ataxia, dysphagia (difficulty swallowing), facial paresis (weakness), head shaking, corneal ulcers, nystagmus and facial hyperesthesia (hypersensitivity to touch and sound). Once that joint fuses, a minor force can fracture the bones involved. These fractures can cause the clinical onset of signs or death. There have been reports of horses returning to athletic activity (approx. 60%) after surgery. Since he still has this condition on the left side, it will be important for his owners to continue monitoring for the development of left-sided neurologic deficits as time progresses.
About the author
Shana Lemmenes, CVT, VTS-EVN, is a senior largeanimal technician at the University of Minnesota. She is also a regional contact (Canada) for AAEVT and holds the Member at Large position with AEVNT. She enjoys spending time with her family, friends, dogs and horses. ModernEquineVet.com | Issue 5/2017
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