Diagnostic utility of trigeminocervical reflex and quantitative sensory testing in horses with trigeminal-mediated headshaking.

TCR testing shows promise as an objective adjunct diagnostic tool for trigeminal-mediated headshaking in horses.

This prospective case-control study evaluated trigeminal nerve (TN) function in horses with trigeminal-mediated headshaking (TMHS) using trigeminocervical reflex (TCR) testing and quantitative sensory testing (QST). Twelve horses with TMHS, four with secondary headshaking (sHS), and 14 headshaking-free controls were enrolled. TCR was assessed via automated threshold-tracking with infraorbital nerve stimulation and concurrent splenic muscle electromyography in unsedated horses. QST included mechanical nociceptive, tactile sensory, and thermal nociceptive threshold evaluations at bilateral sites. Horses with TMHS demonstrated significantly lower TCR thresholds compared to controls (0.82 ± 0.22 mA vs. 1.16 ± 0.30 mA; P = .003), with a large effect size (Hedges' g = 1.24). Univariate logistic regression yielded good predictive performance for TMHS (R² = 0.73; AUC = 0.83), supporting TCR as a potentially useful adjunct diagnostic tool. No significant bilateral asymmetry was found in TMHS horses, though sHS horses showed lower thresholds on the affected side. QST did not differentiate TMHS horses from controls, possibly reflecting heterogeneous somatosensory phenotypes or limitations in the QST protocol's sensitivity. The lower TCR thresholds observed provide objective neurophysiological evidence of altered TN function in TMHS. These findings suggest TCR testing may offer clinicians a more objective means of confirming TN sensitization in suspected TMHS cases, though further studies with larger populations are needed to validate its diagnostic utility in clinical practice.

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