To identify common imaging characteristics in LGI1- and CASPR2-antibody mediated disorders, and how these differ from non-autoimmune disorders such as infectious encephalitis and Creutzfeld-Jakob Disease; CJD.

LGI1- and CASPR2-antibody encephalitis can present with acute to subacute onset confusion, amnesia and seizures. Early recognition and treatment help optimise patient outcomes and salient MRI features can aid diagnosis. Two disorders commonly confused with these syndromes are viral encephalitis and CJD. Here, we asked whether patients with LGI1- and CASPR2-Antibody mediated encephalitis showed characteristic findings on MRI brain to help expedite diagnosis and distinguish the illness from these differentials.

This was a retrospective cross-sectional analysis of patients referred to the Oxford Autoimmune Neurology Group. MRI brains from 97 patients were reviewed blinded and independently by two neuroradiologists. Patients included those with antibodies against LGI1 (N=44), CASPR2 (N=17), LGI1 and CASPR2 (N=4),patients with proven viral encephalitis (N=22) and CJD (N=10). Statistical analyses (e.g. Chi-square test) were performed to identify differences between and within groups, and correlate imaging findings with clinical syndromes.

T2 hyperintensity of the mesial temporal lobe was common in LGI1- and CASPR2-Antibody mediated disease (43/65, 66%). Compared to viral encephalitis, this is more likely to be bilateral (24/43; 56% vs 5/18; 28%. P=0.046), and less likely to extend to other structures (8/43; 19% vs 17/18; 94%. P<0.001), or be associated with oedema (12/65; 19% vs 13/22; 59%, P<0.001). Notably, true diffusion restriction was not seen in any antibody-mediated cases (0/60 vs 16/22; 73%. P<0.001) and contrast enhancement was rare (1/22; 5% vs 7/17; 41%. P=0.013).

In the correct clinical context, highly characteristic imaging findings may be used to assist the diagnosis of LGI1- and CASPR2-Ab mediated encephalitis. In particular, the absence of diffusion restriction and contrast enhancement supports these diagnoses and differentiates them from other common differentials.