Headshaking study suggests new diagnostic aid for horses
Bottom line
Trigeminal-mediated headshaking study points to new diagnostic aids in horses
Researchers reporting in the Journal of Veterinary Internal Medicine evaluated two ways to assess trigeminal nerve function in horses with trigeminal-mediated headshaking, a painful and still difficult-to-confirm condition that’s largely diagnosed by exclusion. In the September-October 2026 issue, Melanie J. Käfer-Karrer, Claudia Spadavecchia, and Mathieu de Preux reported that horses with trigeminal-mediated headshaking had lower trigeminocervical reflex, or TCR, thresholds than controls, while quantitative sensory testing, or QST, identified altered facial sensation in a subset of cases. The paper builds on earlier work from the same group, including a 2025 case report, and adds evidence that objective neurophysiologic testing may help distinguish affected horses from healthy animals and horses with secondary headshaking. (academic.oup.com)
Why it matters: For equine veterinarians, the appeal is straightforward: there’s still no single definitive test for trigeminal-mediated headshaking, and current workups typically rely on history, clinical signs, and ruling out other causes such as dental, sinus, ocular, ear, upper airway, tack-related, or cervical problems. UC Davis notes that no specific or curative treatment exists, and severe cases can compromise welfare or even lead to euthanasia. Against that backdrop, a test with a reported area under the ROC curve of 0.83 for TCR threshold could become a useful adjunct, especially if future studies confirm repeatability, define cutoffs, and show how results change with seasonality or treatment response. QST may be more useful for phenotyping sensory abnormalities than as a stand-alone diagnostic, based on the available summary. (ceh.vetmed.ucdavis.edu)
What to watch: The next step is validation in larger cohorts and real-world referral settings, including whether TCR or QST can track disease severity, seasonal flare-ups, or response to interventions such as PENS or rTMS. (beva.onlinelibrary.wiley.com)
Key facts
- Study
- Diagnostic utility of trigeminocervical reflex and quantitative sensory testing in horses with trigeminal-mediated headshaking
- Journal
- Journal of Veterinary Internal Medicine
- Issue
- September-October 2026
- Condition
- Trigeminal-mediated headshaking
- Main finding
- Affected horses had lower trigeminocervical reflex thresholds than controls
- Secondary finding
- Quantitative sensory testing identified altered facial sensation in a subset of affected horses
- Diagnostic performance
- TCR threshold model had an AUC of 0.83
- Comparison groups
- Horses with trigeminal-mediated headshaking, controls, and horses with secondary headshaking
A new Journal of Veterinary Internal Medicine study suggests equine clinicians may be getting closer to an objective diagnostic aid for trigeminal-mediated headshaking, one of the more frustrating and welfare-relevant syndromes in equine practice. The September-October 2026 paper examined trigeminocervical reflex and quantitative sensory testing in affected horses and found that TCR thresholds, in particular, showed promise for distinguishing trigeminal-mediated headshaking from comparison groups. (academic.oup.com)
That matters because trigeminal-mediated headshaking remains a diagnosis that’s usually reached only after a long rule-out process. The condition, formerly often called idiopathic headshaking, is associated with a lowered activation threshold of the trigeminal nerve and can produce violent vertical, horizontal, or rotary head movements, snorting, nose rubbing, and signs consistent with neuropathic facial pain. Clinical signs are often triggered by wind, light, sound, or exercise, and many cases are seasonal. UC Davis says there’s still no single diagnostic test and no curative treatment, which helps explain why the search for practical, objective markers has become such a priority. (ceh.vetmed.ucdavis.edu)
According to the article summary on Oxford Academic, the investigators compared horses with trigeminal-mediated headshaking with controls and horses with secondary headshaking. They reported lower TCR thresholds in the trigeminal-mediated headshaking group, and a logistic regression model using TCR threshold as a predictor produced an R² of 0.73 and an AUC of 0.83, with a 95% confidence interval of 0.58 to 0.94. The same summary says QST was streamlined to two facial sites per modality to improve feasibility and horse cooperation, and that altered sensory findings were present in a subset rather than uniformly across all affected horses. (academic.oup.com)
The study also fits into a broader research arc. Earlier work established that affected horses can have abnormally low thresholds for trigeminal nerve activation on sensory nerve conduction testing, helping support the neuropathic pain model. More recent studies have looked at MRI asymmetry, pain scoring between episodes, and tools such as accelerometers and structured severity scoring to make diagnosis and monitoring less subjective. A 2025 clinical commentary accompanying the Bern group’s case report called QST and related threshold testing a promising technique, while also stressing that quantifying pain is important for welfare assessment, not just diagnosis. (academic.oup.com)
Industry and expert commentary around the condition has been consistent on one point: even incremental diagnostic progress is valuable. The UC Davis equine neurology group describes trigeminal-mediated headshaking as a globally recognized disorder affecting about 1% of horses, with serious consequences for performance, safety, and quality of life. In a recent The Horse overview drawn from Equine Disease Quarterly, the condition was again framed as severe facial pain tied to inappropriate trigeminal firing and a major management challenge. That context helps explain why a test that may reduce diagnostic uncertainty, even if it doesn’t replace a full workup, is likely to draw attention from referral clinicians. (ceh.vetmed.ucdavis.edu)
Why it matters: For veterinary professionals, the potential value of TCR and QST is less about replacing clinical judgment and more about sharpening it. Headshaking cases often require extensive exclusion of primary disease, and imaging studies have shown that a meaningful minority of horses presenting with headshaking do have treatable underlying causes. If TCR can reliably support a trigeminal-mediated diagnosis, it could help veterinarians triage cases, communicate prognosis more clearly to pet parents, and decide when to move from diagnostic escalation toward management of neuropathic pain. It could also support more standardized enrollment in future clinical trials, something the field needs if therapies are going to be compared meaningfully. (equimanagement.com)
There are still important caveats. The available summary suggests a relatively small study population, and the confidence interval around the AUC is fairly wide, which usually signals uncertainty that should be tested in larger cohorts. Seasonal expression is another unresolved issue. The 2025 commentary specifically noted that testing during seasonal exacerbation would be a logical next step, since trigeminal activation thresholds may not be static across the year. And while TCR appears more immediately promising as a diagnostic discriminator, QST may prove most useful for characterizing sensory phenotypes or monitoring change over time rather than serving as a binary test. (academic.oup.com)
What to watch: Watch for follow-up studies that establish practical cutoff values, assess repeatability across operators and seasons, and test whether these measures correlate with validated severity scores or response to interventions such as percutaneous electrical nerve stimulation and repetitive transcranial magnetic stimulation. If those data hold up, TCR could move from an intriguing research tool to a meaningful part of the referral-hospital workup for suspected trigeminal-mediated headshaking. (equimanagement.com)