Anti-CASPR2 limbic encephalitis (CASPR2-LE) is a rare neurological disorder primarily affecting males over the age of 50. It is mediated by an autoimmune antibody response in the central nervous system (CNS) against the cellular adhesion molecule contactin-associated protein-like 2 (CASPR2). This protein plays an important role in the trafficking of KV1 channels under the myelin sheath in the juxtaparanodal region of myelinated axons. It is mostly present in the neurons of the limbic system, basal ganglia, and other motor related and sensation areas (Qin, Yang, Zhu, Wang, & Shan, 2021). This distribution explains the diverse clinical manifestations of the disease, primarily characterized by cognitive impairment. Other manifestations include cerebellar ataxia, hyperkinetic movement disorders (HMDs), seizures, and neuropathic pain, which all typically develop around 10.4 months after onset. At last visit, memory impairment is seen in 69% of the patients, cerebellar ataxia in 42% of the patients, and functional dependency in 25% of the patients. Even though most patients' symptoms improve with immune-active treatments, up to 69% of them have long-term memory impairments due to damage to hippocampal structures (Benoit et al., 2023). Research has primarily focused on understanding the disease's clinical features, underlying mechanisms, and potential treatment options. On the other hand, it is shown that MRIs performed at baseline show signal changes in the hippocampus in 62-71% of the patients, and these changes are subject to variations in subsequent follow-up scans, that differ widely among patients as mentioned before (Bien et al., 2017). And since the dynamics of hippocampal volume changes and its association with the development of hippocampal atrophy and long-term cognitive impairment are not well studied yet in CASPR2-LE, we primarily aim to examine the longitudinal changes of hippocampal volume in anti-CASPR2 Limbic Encephalitis (CASPR2-LE) patients to examine whether it correlates to the development of anterograde amnesia and hippocampal atrophy on follow-up.

Inclusion Criteria:

• Patients with a definite diagnosis of CASPR2-antibody-associated encephalitis
• available MRI records
• Ascertained positivity for CASPR2-antibodies in CSF

Exclusion Criteria:

• Positivity for another antibody against neural or glial antigens
• MRI images not available
• Not enough clinical data to ascertain outcome

Patients will be included from the from the database of the French Reference Centre for Paraneoplastic Neurological Syndromes and Autoimmune Encephalitis (Lyon, France)