The Multiple Faces of Myoclonus in Dogs and Cats

Presentation Description / Summary: Myoclonus refers to a sequence of repeated, variably rhythmic, brief shock-like jerks resulting from the sudden involuntary contraction (positive) or inhibition of contraction (negative) of one or more muscles, leading to movement of the affected body part. In veterinary neurology, although there is no official classification system, an informal classification into “epileptic” and “non-epileptic” myoclonus is usually made at a clinical level based on clinical features, accompanying neurologic signs, and response to antiseizure drugs. Over the last ten years, multiple studies and case reports have highlighted the occurrence of new and different forms of myoclonic syndromes in dogs and cats. During this lecture, we will investigate the many faces of myoclonus in dogs and cats. We will explore both old and new additions to the myoclonic syndromes in these species, such as juvenile myoclonic epilepsy, feline audiogenic reflex seizures, spontaneous late-onset myoclonic epilepsy, drug-induced myoclonus, encephalitis-associated myoclonus, degenerative encephalopathy-associated myoclonus, post-hypoxic myoclonus, propriospinal myoclonus, spinal myoclonus, and their mimics (hyperekplexia, dystonic facial seizures). A deeper insight into the pathophysiology, possible classification, and treatment will be provided based on recent literature. Finally, we will discuss the newest (2025) classification of myoclonus in human neurology, developed by the International Association of Parkinsonism and Related Disorders, which classifies myoclonus based on Axis Ia (clinical features), Axis Ib (neurophysiological features), and Axis II (etiology).