Interval magnetic resonance imaging in feline limbic encephalitis associated with LGI1-antibodies: a case series

Leucine-rich glioma-inactivated 1 antibody encephalitis (LGI1-Ab-E) is an autoimmune limbic encephalitis that is well described in humans and currently increasingly recognised in cats. Acute MRI findings have been reported, however longitudinal imaging data in feline cases are lacking. The present study describes three young domestic shorthair cats presented with cluster focal to generalized tonic-clonic seizures with variable neurological deficits. Brain MRI at onset revealed bilateral limbic abnormalities, characterised by T2-weighted and FLAIR hyperintensities involving the hippocampus and piriform lobes. One cat additionally showed thalamic and brainstem involvement. Cerebrospinal fluid findings were normal or showed mild mixed pleocytosis. Serum testing confirmed anti-LGI1 antibodies in all cats (titres 1:40–1:320). Follow-up MRI (eight weeks to 27 months) demonstrated persistent limbic T2-weighted and FLAIR hyperintensities in all cases. In one cat, contrast enhancement resolved over time without clear evidence of structural atrophy, although the detection of subtle atrophy may have been limited by the use of low-field MRI. In another cat, follow-up MRI showed progression to typical bilateral medial temporal lobe hyperintensities with contrast enhancement and additional brainstem abnormalities. In the third cat, follow-up MRI revealed diffuse cerebral atrophy, most pronounced in the hippocampal regions, with concurrent cerebellar atrophy. Clinical outcomes ranged from persistent refractory seizures to neurological improvement under anti-seizure and immunosuppressive treatment. To our knowledge, this is the first report of serial MRI findings in feline LGI1-Ab-E with serological confirmation. The imaging evolution mirrors human disease, progressing from inflammatory changes to chronic structural changes. Although only three cases were available, occasional extra-limbic MRI abnormalities may occur in feline LGI1-Ab-E; however, their frequency and pathogenic relationship to LGI1-associated inflammation remains uncertain. These findings could support feline LGI1-Ab-E as a naturally occurring translational model and highlight the value of longitudinal MRI in characterising disease progression.