Utility of the Clinical Assessment Scale for Autoimmune Encephalitis (CASE) Score to Define Relapse in the Scarcity of Biomarker Footprints in Anti-Leucine-Rich Glioma-Inactivated Protein 1 Encephalitis: A Case Report

Anti-leucine-rich glioma-inactivated protein 1 (anti-LGI1) encephalitis is an autoimmune encephalitis caused by autoantibodies against LGI1 and often presents with subacute cognitive decline, behavioral symptoms, and seizures. Relapses can occur after a favorable treatment response to the first-line immunotherapy, whereas decision-making on relapses may sometimes be challenging. Here, we report the case of a 71-year-old woman who developed cognitive decline, psychiatric symptoms, and faciobrachial dystonic seizures over three months. The patient was diagnosed with anti-LGI1 encephalitis based on high signal intensity on fluid-attenuated inversion recovery in the medial temporal lobes and antibody test results. One month after improvement with first-line immunotherapy, psychiatric symptoms and cognitive decline relapsed. The neurological findings and anti-LGI1 antibody profiles at the relapse did not converge on the typical constellation of diagnostic signatures of anti-LGI1 encephalitis. However, the deterioration of the Clinical Assessment Scale for Autoimmune Encephalitis (CASE) score indicated substantial worsening of symptoms. The case highlights that the assessment using the CASE score over time may be beneficial to define relapse in a setting with insufficient laboratory evidence of anti-LGI1 encephalitis.