New Feline Epilepsy Syndrome: Levetiracetam Effective in Late-Onset Myoclonus

Spontaneous Late-Onset Myoclonic Epilepsy in Cats: 15 Cases (2015–2023)

Theofanis Liatis, Athina Karpozilou, Alberta De Stefani

Background

Myoclonus—brief, shock-like jerks due to sudden involuntary muscle activity—can be epileptic or non-epileptic. In cats, recognized epileptic phenotypes include temporal lobe epilepsy and feline audiogenic reflex seizures (FARS). This study reports a novel epileptic syndrome in older cats: spontaneous late-onset myoclonic epilepsy (SLOME), unrelated to auditory triggers, occasionally accompanied by generalized tonic–clonic seizures.

Methods

A retrospective, two-center case series (2015–2023) included cats with spontaneous, non-reflex myoclonus (head or body). Inclusion required complete medical records; exclusion ruled out audiogenic or photogenic triggers. Data collected: signalment, neurological exams, MRI/CT, CSF analysis, infectious/autoimmune serology, treatments, and follow-up. Myoclonus was confirmed by clinical or video assessment.

Results

Fifteen cats (median age 13.2 years; 73% domestic shorthair) were included. All exhibited head myoclonus; 20% also had thoracic limb involvement; 7% had generalized involvement. Episodes were brief (<1 min), daily or weekly in nearly half, and persisted despite distraction. Two cats also had generalized tonic–clonic seizures. MRI (6 cats) was normal in most, though one had cortical atrophy and another a pituitary mass. CSF was normal in all 4 tested cats. No infectious or LGI1 autoimmune antibodies were detected. Nine cats received antiseizure treatment: 7 levetiracetam, 1 phenobarbital, and 1 both sequentially. All treated cats improved, with marked reduction or cessation of myoclonus. One year after levetiracetam, recurrence in one cat was controlled with added phenobarbital. Median follow-up for treated cats was 128 days (range 30–300). Long-term owner questionnaires confirmed persistent but sporadic episodes in some untreated cats.

Limitations

This was a retrospective study with small sample size. Electroencephalography was not performed, so epileptic origin is inferred from clinical phenotype and levetiracetam responsiveness. Owner recall bias and incomplete follow-up may have affected data accuracy.

Conclusions

SLOME is a distinct seizure phenotype in older cats, presenting as spontaneous head-focused myoclonus, often progressive, occasionally with generalized seizures. Unlike FARS, it lacks audiogenic triggers. Levetiracetam provided consistent therapeutic benefit, suggesting an epileptic origin. Early recognition may improve quality of life and limit seizure progression.

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