Monocular ictal nystagmus in a dog: potentially a newly recognized focal seizure phenotype.

A 3-year-old, male neutered toy Chinese crested powderpuff dog was presented with an acute onset obtundation that progressed to status epilepticus. On presentation, neurological examination was localized to a right forebrain lesion. Bizarre episodes, consisting of disconjugate nystagmus of the left eye, medial strabismus of the right eye with convergent-retraction movements in both eyes, were recorded. Head magnetic resonance imaging revealed intra-axial multifocal lesions affecting the right fronto-temporal cortices and dorsal paramedian thalamus. Cerebrospinal fluid analysis revealed a marked mononuclear pleocytosis. Electroencephalographic recordings revealed recurrent medium-amplitude interictal isolated spikes, and suspected epileptic spikes alongside with eye movement that were mainly visible in the right hemisphere. The presumptive diagnosis was meningoencephalitis of unknown origin. Despite treatment, the dog died. This is a report of monocular nystagmus with a presumptive epileptic origin in veterinary medicine, a rare clinical sign in human patients.