Ataxia: What the Research Says
Evidence from 30 peer-reviewed studies
4 Cohort Study
17 Case Report
9 Expert Opinion
What Professionals Should Know
- •Ataxia severity at presentation is a critical prognostic indicator—horses with grade ≥4/5 ataxia have poor prognosis for return to sport and high mortality risk
- •Development of urinary complications and vasculitis signs warrant guarded prognosis; horses with both complications showed zero return to previous performance
- •Most EHM-affected horses can return to some level of exercise, but pre-outbreak performance recovery is uncertain; owners should manage expectations and plan for potential permanent career changes
- •EHV-1 genotype alone should not be used to predict clinical severity or prognosis in horses with EHM; clinical management should focus on individual presentation rather than genotype
- •Expect urinary incontinence more commonly in horses infected with D752 genotype, which may influence monitoring and supportive care strategies
- •Both D752 and N752 genotypes cause clinically significant myeloencephalopathy requiring equivalent diagnostic and therapeutic approaches
- •TMS with motor evoked potential recording may offer an objective diagnostic complement to traditional neurological exams and radiography for evaluating ataxic horses
- •The Bayesian latent class approach provides a statistical framework for validating diagnostic tests when necropsy confirmation is not available in clinical cases
- •Consider TMS as a potential additional diagnostic modality when spinal cord dysfunction is suspected but conventional imaging findings are equivocal
- •Motion capture gait analysis provides objective measurement of ataxia when subjective clinical assessment is unreliable, particularly for mild cases
- •Blindfolding during neurological examination exacerbates movement variability in ataxic horses, making clinical signs more apparent and improving diagnostic discrimination
- •Distal limb kinematics (particularly hoof displacement) are more sensitive indicators of ataxia than proximal markers when assessed with motion capture
- •Recognize cerebellar abiotrophy as a differential diagnosis in neonatal foals presenting with ataxia and incoordination, particularly those showing poor response to supportive care.
- •Quarter Horse breeders should be aware that cerebellar abiotrophy is no longer limited to Arabian horses; genetic screening and pedigree investigation may be warranted.
- •Supportive therapy with antibiotics, corticosteroids, DMSO, and vitamins may provide temporary clinical improvement but does not alter the progressive nature of this condition; euthanasia may be the humane endpoint.
- •Computer-assisted surgery may offer a viable alternative to traditional intervertebral fusion for cranial articular process fractures, with potential for better functional outcomes and return to work.
- •Even with postoperative complications (ataxia, myopathy), careful management can result in resolution and return to ridden exercise within 1 year.
- •Minimizing callus formation through accurate internal fixation is critical to prevent secondary spinal cord compression in cervical fractures.
- •EHM cases presenting with recumbency may have favorable long-term prognoses with intensive supportive care including sling support, fluid therapy, and aggressive management of secondary complications.
- •Prolonged bladder catheterization and lavage, combined with systemic antimicrobials, effectively prevent and manage secondary urinary tract infections in recumbent EHM horses.
- •Monitor for multiple secondary complications (ophthalmic, dermatologic, urinary) in recumbent EHM cases and implement preventive measures early, as these resolve well with appropriate treatment.
- •Interbody fusion with polyaxial pedicle screws and rods can improve cervical ataxia in horses with vertebral compression, with 60-75% achieving meaningful functional improvement
- •Expect high seroma formation rates (90%) and postoperative pain in most cases; plan appropriate management protocols for these anticipated complications
- •This technique appears safer than traditional ventral fusion approaches with comparable outcomes, making it a viable alternative for referral cases
- •Include TBEV in your differential diagnosis list for horses presenting with acute neurologic signs (ataxia, proprioceptive deficits) if they are from or have travelled through endemic regions of Switzerland or other TBEV-endemic areas
- •Tick prevention and control measures are essential for horses in TBEV endemic regions, as the virus is transmitted by tick bites to multiple species including humans and horses
- •Request appropriate serological testing (virus neutralization test and TBEV-specific IgM antibodies) when neurologic disease is suspected in at-risk populations, as standardized diagnostic criteria are currently lacking
- •Recognize that T. micrantha leaves, despite being palatable to horses, cause rapid-onset neurological signs including ataxia and sialorrhoea that progress to recumbency and death within days of consumption
- •Counsel horse owners in regions where T. micrantha is present (throughout the Americas) to prevent access to this tree, as there is no identified treatment and poisoning is often fatal
- •Be aware that CNS lesions may occur without significant liver involvement, so hepatic parameters alone should not be used to rule out T. micrantha toxicity in horses with acute neurological signs
- •Hamartomatous myelodysplasia should be considered as a differential diagnosis in young horses presenting with unexplained progressive neurologic signs, particularly muscle rigidity or ataxia
- •The location and extent of spinal cord lesions (cervical vs lumbar, central vs peripheral) may influence the specific clinical presentation and severity of neurologic deficits
- •Definitive diagnosis requires advanced imaging (MRI) and histopathological examination; clinical signs alone cannot differentiate this condition from other myelopathies
- •Embryo transfer practitioners should be aware that placental abnormalities detected at delivery may indicate serious neoplastic disease with potential fetal transmission
- •Foals presenting with unexplained neurological signs (ataxia, lethargy) combined with urinary dysfunction warrant thorough investigation for metastatic neoplasia, particularly in cases where placental pathology was noted
- •This case highlights the importance of thorough placental examination and necropsy in embryo transfer programs to identify rare but critical complications
- •Atlanto-occipital CSF collection can be performed on standing horses using ultrasound guidance and sedation alone, avoiding the need for general anaesthesia in horses with severe neurological signs or where anaesthesia is contraindicated
- •Proper safety measures and close observation remain essential, as this is a novel application with limited evidence in ataxic horses
- •Further research on larger numbers of ataxic horses is needed before recommending this as standard alternative to anaesthetised collection
- •NAD/EDM in American Quarter Horses does not appear to be caused by mutations in the TTPA gene, suggesting the genetic basis differs from human vitamin E deficiency disorders
- •Understanding the true genetic cause of NAD/EDM is essential for developing accurate genetic testing and breeding programs to reduce disease incidence
- •Vitamin E supplementation recommendations for NAD/EDM prevention may require different approaches than those used for TTPA-related deficiencies
- •Myeloscopy should be considered when cervical myelography results do not correlate with clinical signs and imaging findings in suspected cervical vertebral stenotic myelopathy cases.
- •Relying solely on myelography for localizing cervical spinal cord compression may lead to incorrect diagnosis; direct endoscopic visualization can provide more accurate anatomical information.
- •In horses with progressive neurological deficits and equivocal imaging, cervical vertebral canal endoscopy offers a valuable diagnostic tool to guide treatment decisions before irreversible spinal cord damage occurs.
- •Include free-living nematode infection (H. gingivalis) in the differential diagnosis when horses present with progressive CNS signs that do not respond to standard treatment, though this remains an extremely rare cause
- •Be aware that this parasite's taxonomy has changed; older literature may refer to it as Micronema deletrix or Halicephalobus deletrix, which may affect literature searches
- •Recognize that despite the rarity of this condition, CNS helminthic infections in horses warrant comprehensive post-mortem examination and histopathology to establish definitive diagnosis
- •Ventral partial ostectomy of the dens is a viable surgical option when conservative closed reduction fails for atlantoaxial subluxation.
- •This technique can resolve clinical signs including ataxia and neck stiffness while maintaining long-term joint stability.
- •Successful outcomes depend on achieving decompression and anatomic re-alignment, requiring surgical expertise and intraoperative imaging.
- •Caudal cervical articular process joint disease should be considered in the differential diagnosis for horses presenting with ataxia and paresis, particularly older animals
- •Radiographic evaluation of the C5-C6 and C6-C7 joints may help identify articular process enlargement that could explain neurological signs
- •Age-related changes in cervical articular process joints appear to be a normal finding; the clinical significance of enlargement relative to neurological signs requires further investigation
- •Ventral locking compression plates offer a viable alternative to basket fusion in young/small horses for cervical stabilization, with documented long-term success
- •Careful screw selection is critical in immature horses—avoid self-drilling screws that may migrate; use appropriately sized non-self-drilling screws for secure fixation
- •Neurologic recovery in cervical stenotic myelopathy can be substantial (2.5 grade improvement) with appropriate surgical stabilization, even in very young foals
- •This condition represents a novel breed-specific cervical myelopathy in Texel and Beltex sheep with a distinct pathophysiology (fatty nodule prolapse) not previously documented in these breeds
- •Young sheep presenting with ataxia and weakness should be evaluated with CT myelography at C6-C7 to differentiate this adipose-related compression from other causes
- •Further research is needed to determine hereditary risk factors and etiology in order to implement breeding strategies to reduce incidence in affected breeds
- •West Nile virus should be included in differential diagnoses for horses presenting with acute ataxia, hindlimb paresis, or progressive tetraplegia, particularly during late summer and autumn months
- •Geographic regions with suitable climatological and environmental conditions may support WN virus transmission via mosquito vectors—implement appropriate vector control and biosecurity measures
- •Prognosis is relatively favorable with 57% recovery rate in this outbreak; however, cases progressing to recumbency may require intensive management and supportive care
- •Systemic complications such as urinary dysfunction and signs of vasculitis during EHM outbreaks are critical prognostic indicators—horses developing these require intensive monitoring and management as they have significantly worse outcomes regardless of initial neurological severity
- •Even identical EHV-1 strains can cause variable disease severity between outbreaks; clinical context matters for prognosis and the presence of secondary complications is more predictive than the causative strain alone
- •Early recognition and aggressive management of systemic signs (urinary/vascular complications) may be key to improving survival and return-to-competition rates in EHM cases
- •Recurrent fevers and infections should prompt immunodeficiency screening; diagnosis requires two separate IgG measurements below 10.00 g/L
- •Clinical management of CVID is intensive and expensive—early diagnosis is critical for discussing realistic prognosis and euthanasia decisions with owners
- •B cell counts alone are not diagnostic; immunological findings must be interpreted alongside clinical signs and serological data for definitive diagnosis
- •Diagnostic SI joint injections carry substantially higher complication rates than therapeutic injections; clinicians should weigh diagnostic benefit against risk of hindlimb ataxia (40% complication rate)
- •Hindlimb weakness/ataxia is the expected complication pattern across all injection types; owners should be counselled on this risk and appropriate monitoring protocols established
- •Although rare, serious complications including death have been reported; ensure informed consent, appropriate facilities for observation/emergency management, and consider whether diagnostic information could be obtained through alternative methods
- •Before administering antibiotics to horses, carefully review and optimize the specific drug choice, formulation, route, and dosage to minimize risk of serious adverse effects including diarrhea, colitis, and neurologic complications.
- •Be alert for adverse reactions with commonly used equine antibiotics (sulfonamides, penicillins, cephalosporins, fluoroquinolones) and monitor horses closely during treatment for gastrointestinal, renal, otic, cardiac, and neurologic signs.
- •Work with your veterinarian to balance the benefits of antibiotic therapy for bacterial infections against the documented risks of adverse effects specific to equine patients.
- •Use a systematic approach to neurological examination and localisation when evaluating ataxic horses rather than jumping to conclusions
- •Build your differential diagnosis list based on where the lesion is likely located in the nervous system and the patient's risk factors
- •Tailor your diagnostic plan (imaging, bloodwork, etc.) to the most probable conditions rather than running every test available
- •Not applicable - this review focuses on feline Borna disease and has limited direct application to equine practice
- •Recognize perennial ryegrass-associated tremor and ataxia as a variable clinical syndrome; affected horses may show subtle signs during rest but marked incoordination during movement or when vision is compromised
- •Clinical severity does not reliably correlate with plasma lolitrem B levels, so diagnosis cannot be ruled out based on toxin concentration alone
- •Manage affected horses by removing access to contaminated ryegrass pasture; monitor for associated dermatological and respiratory signs that may indicate multi-toxin exposure
- •Understanding cervical APJ anatomy is essential for diagnosing and treating horses presenting with neck-related ataxia and weakness
- •Clinicians should consider APJ involvement in cases of spinal cord compression, as disorders of these joints can produce severe neurological signs
- •This anatomical reference provides foundation for improved diagnostic imaging interpretation and surgical planning in cervical conditions
- •Magnetic motor evoked potentials provide a non-invasive, painless diagnostic tool to confirm cervical spinal cord lesions and assess motor pathway integrity in ataxic horses
- •This technique is sensitive enough to detect subclinical or subtle lesions that may not be apparent from clinical examination alone
- •Abnormal potentials may persist despite clinical improvement, so results should be interpreted alongside clinical progression rather than as a measure of recovery
Key Research Findings
68% of EHM-affected horses returned to exercise, with 52.9% achieving their pre-outbreak performance level
Horses with ataxia grade ≥4/5 at admission had increased fatality rate and only 10% chance of returning to pre-outbreak performance
None of the horses with both vascular and urinary complications returned to previous performance level
Prior EHV-1 vaccination and urinary complications were associated with 71.4% and 43.7% fatality rates respectively
EHV-1 genotype (D752 vs N752) did not significantly affect lethargy, fever, ataxia, or outcome in 65 horses with EHM (P > 0.05)
Urinary incontinence was significantly more frequent in horses infected with D752 genotype (P = 0.04)
No difference in frequency of D752 versus N752 genotypes was found among the 65 EHM cases, contrary to previous studies
Breed distribution differed between genotype groups, with Quarter Horses and Saddlebreds overrepresented in D752 group and Warmbloods underrepresented
Transcranial magnetic stimulation with magnetic motor evoked potentials shows promise as a diagnostic tool for spinal cord dysfunction in horses
A Bayesian latent class model was developed to overcome the absence of a gold standard for diagnosing spinal cord dysfunction in living horses
Current presumptive diagnosis relies primarily on neurological examination and cervical radiography
Coefficient of variation in maximum vertical displacement of pelvic and thoracic distal limbs provided good diagnostic yield for ataxia grade ≥2
Thoracic hoof marker achieved AUC of 0.81 with 64% sensitivity and 90% specificity in normal conditions
Blindfolding increased diagnostic accuracy with hoof marker AUC improving to 0.89 with 82% sensitivity and 90% specificity
Motion capture can objectively assess ataxia severity when clinical agreement among experienced assessors is poor
Evidence Base
Long-term performance of show-jumping horses and relationship with severity of ataxia and complications associated with myeloencephalopathy caused by equine herpes virus-1.
de la Cuesta-Torrado María, Velloso Alvarez Ana, Neira-Egea Patricia et al. (2024) — Journal of veterinary internal medicine
Cohort Study
Equine herpesvirus-1 genotype did not significantly affect clinical signs and disease outcome in 65 horses diagnosed with equine herpesvirus-1 myeloencephalopathy.
Pusterla N, Hatch K, Crossley B et al. (2020) — Veterinary journal (London, England : 1997)
Cohort Study
Accuracy of transcranial magnetic stimulation and a Bayesian latent class model for diagnosis of spinal cord dysfunction in horses.
Rijckaert Joke, Raes Els, Buczinski Sebastien et al. (2020) — Journal of veterinary internal medicine
Cohort Study
Kinematic discrimination of ataxia in horses is facilitated by blindfolding.
Olsen E, FouchÉ N, Jordan H et al. (2018) — Equine veterinary journal
Cohort Study
Cerebellar abiotrophy in a quarter horse foal.
Primo A L M, Assis D M, Santos V G S et al. (2025) — Journal of equine veterinary science
Case Report
Internal fixation of a fractured cranial articular process of the sixth cervical vertebra by means of computer-assisted surgery in a Warmblood gelding.
Käfer-Karrer Melanie J, de Preux Mathieu, Van der Vekens Elke et al. (2025) — Veterinary surgery : VS
Case Report
Medical management and positive outcome after prolonged recumbency in a case of equine herpesvirus myeloencephalopathy.
Mannini A, Ellero N, Urbani L et al. (2024) — Journal of equine veterinary science
Case Report
Outcomes after cervical vertebral interbody fusion using an interbody fusion device and polyaxial pedicle screw and rod construct in 10 horses (2015-2019).
Pezzanite Lynn M, Easley Jeremiah T, Bayless Rosemary et al. (2022) — Equine veterinary journal
Case Report
Neurological disease suspected to be caused by tick-borne encephalitis virus infection in 6 horses in Switzerland.
Magouras Ioannis, Schoster Angelika, Fouché Nathalie et al. (2022) — Journal of veterinary internal medicine
Case Report
Neurotoxicosis in horses associated with consumption of Trema micrantha.
Lorenzett M P, Pereira P R, Bassuino D M et al. (2018) — Equine veterinary journal
Case Report
Spinal Cord Hamartomatous Myelodysplasia in 2 Horses With Clinical Neurologic Deficits.
Taylor K R, MacKay R J, Nelson E A et al. (2016) — Veterinary pathology
Case Report
Equine placental mixed germ cell tumor with metastasis to the foal.
Bockenstedt M M, Fales-Williams A, Haynes J S (2015) — Veterinary pathology
Case Report
Ultrasound-guided atlanto-occipital puncture for cerebrospinal fluid analysis on the standing horse.
Depecker M, Bizon-Mercier C, Couroucé-Malblanc A (2014) — The Veterinary record
Case Report
Pedigree analysis and exclusion of alpha-tocopherol transfer protein (TTPA) as a candidate gene for neuroaxonal dystrophy in the American Quarter Horse.
Finno C J, Famula T, Aleman M et al. (2013) — Journal of veterinary internal medicine
Case Report
Cervical vertebral canal endoscopy in a horse with cervical vertebral stenotic myelopathy.
Prange T, Carr E A, Stick J A et al. (2012) — Equine veterinary journal
Case Report
Fatal equine meningoencephalitis in the United Kingdom caused by the panagrolaimid nematode Halicephalobus gingivalis: case report and review of the literature.
Hermosilla C, Coumbe K M, Habershon-Butcher J et al. (2011) — Equine veterinary journal
Case Report
Partial ostectomy of the dens to correct atlantoaxial subluxation in a pony.
Cillán-Garcia Eugenio, Taylor Sarah E, Townsend Neil et al. (2011) — Veterinary surgery : VS
Case Report
Radiographic retrospective study of the caudal cervical articular process joints in the horse.
Down S S, Henson F M D (2009) — Equine veterinary journal
Case Report
Ventral locking compression plate for treatment of cervical stenotic myelopathy in a 3-month-old warmblood foal.
Reardon Richard, Kummer Martin, Lischer Christoph (2009) — Veterinary surgery : VS
Case Report
Compressive cervical myelopathy in young Texel and Beltex sheep.
Penny Colin, Macrae Alastair, Hagen Regine et al. (2007) — Journal of veterinary internal medicine
Case Report
Show 10 more references
Clinical and neuropathological features of West Nile virus equine encephalomyelitis in Italy.
Cantile C, Di Guardo G, Eleni C et al. (2000) — Equine veterinary journal
Case Report
Comparison of clinical variables and outcome of 2 natural equine herpesvirus myeloencephalopathy outbreaks induced by equine herpesvirus-1 A2254/N752 strain in sport horses.
de la Cuesta-Torrado María, Velloso Alvarez Ana, Cárdenas-Rebollo José Miguel et al. (2025) — Journal of veterinary internal medicine
Expert Opinion
Equine common variable immunodeficiency: lessons from 100 clinical cases.
Julia M, Felippe B (2024) — Equine veterinary education
Expert Opinion
Complications following diagnostic and therapeutic sacroiliac joint region injections in horses: A study describing clinicians' experiences.
Nagy Annamaria, Dyson Sue (2023) — Equine veterinary journal
Expert Opinion
Adverse Effect of Antibiotics Administration on Horse Health: An Overview.
Khusro Ameer, Aarti Chirom, Buendía-Rodriguez German et al. (2021) — Journal of equine veterinary science
Expert Opinion
Evaluation of ataxia in the horse
Alcott C. J. (2017) — Equine Veterinary Education
Expert Opinion
Borna disease virus infection in cats.
Wensman Jonas Johansson, Jäderlund Karin Hultin, Holst Bodil Ström et al. (2014) — Veterinary journal (London, England : 1997)
Expert Opinion
Clinical expression of lolitrem B (perennial ryegrass) intoxication in horses.
Johnstone L K, Mayhew I G, Fletcher L R (2012) — Equine veterinary journal
Expert Opinion
The 3D anatomy of the cervical articular process joints in the horse and their topographical relationship to the spinal cord.
Claridge H A H, Piercy R J, Parry A et al. (2010) — Equine veterinary journal
Expert Opinion
The use of magnetic motor evoked potentials in horses with cervical spinal cord disease.
Nollet H, Deprez P, Van Ham L et al. (2002) — Equine veterinary journal
Expert Opinion