Subtle neurologic signs in horses can challenge even experts
Bottom line
The Horse on October 14 highlighted a familiar but often underrecognized clinical problem in equine practice: horses with neurologic disease don't always present with dramatic deficits, and early cases can look more like vague poor performance, unevenness, resistance under saddle, or subtle gait changes. The article points to a 2017 Journal of Veterinary Internal Medicine study in 97 horses showing that even experienced board-certified clinicians had only "good" overall agreement when assessing neurologic abnormalities, with the most variability in mild cases and in judging asymmetry, muscle atrophy, hypermetria, and overall severity. (thehorse.com)
Why it matters: For veterinary professionals, the takeaway isn't just that neurologic disease can be easy to miss, but that the exam itself has recognized subjectivity. That matters when differentiating neurologic disease from lameness, poor performance, or behavioral complaints, and when working up differentials that can include EPM, arboviral encephalitides such as Eastern equine encephalitis and West Nile virus, EHV-1 myeloencephalopathy, degenerative disease, trauma, and metabolic or inflammatory conditions. AAEP and other equine references emphasize a consistent, standardized neurologic examination and careful neuroanatomic localization, while Merck notes that serology alone can be misleading for EPM without appropriate interpretation, including serum:CSF context. (thehorse.com)
What to watch: Expect continued emphasis on standardized field exams, earlier referral of subtle cases, and more discussion of how to distinguish mild neurologic disease from lameness in performance horses. (thehorse.com)
Key facts
- Article date
- October 14, 2026
- Main point
- Horses with neurologic disease may present with vague poor performance, unevenness, resistance under saddle, or subtle gait changes
- Study
- 2017 Journal of Veterinary Internal Medicine study
- Sample size
- 97 horses
- Study setting
- Ohio State veterinary teaching hospital
- Examiner design
- Two board-certified veterinarians examined each horse the same day, one with history and one without
- Agreement finding
- Overall agreement was good, but worse in mild cases
- Hardest findings to judge
- Asymmetry, muscle atrophy, hypermetria, truncal sway, and overall severity grading
- Differential examples
- EPM, Eastern equine encephalitis, West Nile virus, EHV-1 myeloencephalopathy, degenerative disease, trauma, and metabolic or inflammatory conditions
A new article from The Horse is putting a spotlight on one of equine medicine's more frustrating realities: a horse with neurologic disease may not look obviously neurologic. Published October 14, 2026, the piece argues that horses can present as merely "off," uneven, resistant, or underperforming, rather than showing the classic severe signs many pet parents and even referring barns expect. (thehorse.com)
That framing fits with a broader shift in equine practice. Over time, clinicians have become more alert to subtle neurologic presentations, especially in performance horses where mild incoordination, weakness, or abnormal limb placement can be mistaken for lameness or training issues. The Horse ties this challenge to a 2017 JVIM study by Workman and colleagues, conducted at The Ohio State University, which assessed how consistently experienced clinicians recognized neurologic abnormalities in horses. (thehorse.com)
The study included 97 horses examined at the Ohio State veterinary teaching hospital. One board-certified veterinarian examined each horse with knowledge of the history, and a second board-certified internist repeated the exam the same day without that history, using the same standardized protocol. The authors found better agreement in moderately to severely affected horses, but more disagreement in horses with mild signs. According to both the study and The Horse's summary, agreement was strongest for broad determinations such as whether neurologic abnormality, lameness, or ataxia was present, and weakest for deficit asymmetry, muscle atrophy, hypermetria, truncal sway, and overall severity grading. (thehorse.com)
That matters because the differential list is broad, and some of the most important causes are time-sensitive or high-consequence. Merck and AAEP resources note that EPM remains a common infectious neurologic disease in horses in the Americas, while arboviral encephalomyelitides including Eastern equine encephalitis and West Nile virus can produce variable neurologic signs and, in the case of EEE, severe and often fatal disease. AAEP field guidance also advises veterinarians to confirm that a horse is truly neurologic, localize the lesion, and contact state animal health authorities if diseases such as EHV-1 myeloencephalopathy, EEE/WEE/VEE, WNV, or rabies are suspected. (merckvetmanual.com)
Expert commentary in the surrounding equine literature reinforces the same point. An AAEP field-exam paper stresses that clinicians need a repeatable system for the neurologic exam so abnormalities aren't overlooked, and a recent The Horse conference report on neurologic disease signs, diagnosis, and management says subtle changes in gait, posture, or behavior can be the earliest clues. Another recent Horse article on neurologic conditions versus lameness notes that delayed reactions, leaning, and hind-end gait abnormalities can redirect a case away from orthopedic explanations. (ivis.org)
Why it matters: For equine veterinarians, this is less a single-study news item than a reminder about diagnostic process. Mild neurologic disease is exactly where observer variability is highest, yet those are often the cases with major implications for rider safety, biosecurity, treatment selection, and prognosis. In practice, that supports a low threshold for a structured neurologic exam, clear documentation, serial rechecks, and, when warranted, referral for advanced workup. It also argues against overinterpreting isolated test results: Merck specifically notes that EPM serology alone can yield false positives without appropriate serum:CSF interpretation, underscoring that laboratory data should support, not replace, localization and clinical judgment. (pubmed.ncbi.nlm.nih.gov)
The article also lands in a seasonally relevant context. The Horse's own recent coverage includes fall vaccination reminders and a fresh West Nile case report, both of which underscore that infectious neurologic disease remains part of routine risk management, not just referral-hospital medicine. For clinicians, the practical message is that a horse described as resisting, bucking, drifting, or simply going poorly may justify a more deliberate neurologic screen than the presenting complaint alone would suggest. (thehorse.com)
What to watch: The next development to watch isn't likely to be a new drug or regulatory filing, but wider uptake of standardized neurologic scoring, better field differentiation of lameness versus neurologic disease, and continued education around when subtle cases should trigger infectious disease precautions, CSF-based diagnostics, or referral. (aaep.org)