What is the diagnostic approach to seizures in adult horses and how is equine epilepsy managed?

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The diagnostic workup for seizures in adult horses begins with classifying the episode as a reactive seizure, structural epilepsy, or primary epilepsy, using signalment, neurologic examination findings, and targeted diagnostics to guide the pathway.1 Electroencephalography (EEG) is a validated diagnostic tool for equine epilepsy, with recordings obtained under general anesthesia documented in horses across multiple studies.2 General anesthesia is a significant limitation for EEG interpretation, however, as it precludes assessment of cerebrocortical activity during arousal and sleep states essential for characterizing epileptic disorders, may obliterate paroxysmal discharges that support the diagnosis, and can cause burst suppression depending on the anesthetic agent used.2 Standing sedation with sublingual detomidine hydrochloride has been evaluated as an alternative approach, allowing EEG recording during slow-wave sleep (SWS), which facilitates detection of epileptic discharges.2 SWS induced by detomidine reliably produces second-degree atrioventricular (AV) block, which is a normal finding during this sleep state in horses and should not be interpreted as a pathologic cardiac event.2 Decreased heart rate and respiratory rate accompany this state and are expected.2 Sleep facilitates epileptic activity, and paroxysmal discharges supporting an epilepsy diagnosis are most likely to appear during SWS.2 A normal EEG does not rule out epilepsy. The absence of epileptic discharges during a recording is a recognized limitation of EEG in all species.24 For emergency management of active seizures in adult horses, diazepam is the first-line drug. The Merck Veterinary Manual identifies diazepam as the most commonly used drug for seizures and status epilepticus in horses; specific dosing is referenced to disease-specific chapters rather than a single universal protocol.3 Seizure classification in horses follows the same foundational framework used in small animals and dogs: an