More one health: analysis of 315 cats confirms cross-species relevance of naturally- occurring feline LGI1-antibody encephalitis

<h3>Introduction</h3> Encephalitis with antibodies to leucine-rich glioma-inactivated 1 (LGI1-Ab-E) is one of the most common human autoimmune encephalitides. At the 2022 conference, we described 56 spontaneously-occurring feline cases. This update describes 151 LGI1-Ab-E cats from 12 European countries. <h3>Methods</h3> We have screened &gt;300 samples from seizuring cats with our feline-specific LGI1- autoantibody cell based assay (CBA). Paraclinical and clinical features were captured from veterinary and study records. <h3>Results</h3> Of 315 participants, 151 (48%) were CBA-positive (79/148 (53%) female, median age 47 months). Clinical details confirmed an explosive seizure disorder akin to human LGI1-Ab-E with focal seizures (119/129, 92%) and status epilepticus or cluster seizures (103/121, 85%) significantly enriched (p&lt;0.001) in seropositive cases after multiple comparison. Seropositive group mean onset seizures of 16/day significantly exceeded 9 for seronegative cases (p&lt;0.001), and 47/103 (46%) had bilateral hippocampal high signal on MRI (21/81 (26%) seronegative cases, p&lt;0.05). Immunotherapies included steroids, ciclosporin, and IVIG. At last follow-up, 92/113 (81%) had improved seizure control, but 13% (19/146) were euthanised, disproportionately those with refractory seizures. <h3>Conclusion</h3> Naturally-occurring feline LGI1-Ab-E mirrors human LGI1-Ab-E and represents a resource to discover cross-species causation mechanisms. Future research should study long-term outcomes in comparison to human LGI1-Ab-E, and expand feline autoantibody screening.