Introduction Leucine-rich glioma-inactivated 1 (LGI1) is one of the most common surface neuronal autoantigens associated with autoimmune limbic encephalitis (LE) in humans, with hallmarks of personality change, amnesia and seizures. Recently, these autoantibodies were described in domestic cats with LE, likewise with a distinctive phenotype of behavioural change and orofacial seizures.

Methods Using a feline-specific cell-based assay for LGI1-autoantibodies, we tested serum from 123 cats with neurological signs, submitted by veterinary surgeons across Europe. Clinical presentation, investiga- tions, management and outcomes were captured by questionnaire and review of medical records.

Results 56 samples were positive for LGI1-autoantibodies. The median age was 45 months and 34/54 (63%) were female. Most (44/56, 79%) had LE but other clinical syndromes included epilepsy, encephalopathy and feline hyperesthesia syndrome. Focal seizures without generalisation were reported in 42/51 (82%) compared to 25/47 (53%) in seronegative cats (p=0.02). Among seropositive cats, MRI abnormalities were identified in 23/42 (55%), adverse drug reactions in 7/50 (14%), and 8/51 (16%) were euthanised due to refractory seizures or status epilepticus.

Conclusion Many features are common to humans and cats with LGI1-autoantibodies. Feline patients represent a naturally-occurring disease model and an opportunity to benefit health in both species via a bi-directional translational model.