Autoimmune Encephalitis Associated With Anti-Contactin-Associated Protein-Like 2 (Anti-CASPR2) Antibodies in an Elderly Patient: A Case Report.

The leading cause of epilepsy in the elderly is cerebrovascular disease. Autoimmune encephalitis (AE) is an increasingly recognized cause of new-onset seizures in older adults, particularly when no structural lesion or infectious aetiology is identified and when there are unexplained new-onset seizures, particularly in focal status epilepticus. We report the case of a 77-year-old male with anti-contactin-associated protein-like 2 (anti-CASPR2) encephalitis whose initial brain MRI and routine labs were unremarkable. Despite the negative imaging and routine blood tests, clinical evaluation yielded a high Antibody Prevalence in Epilepsy and Encephalopathy (APE2) and the Response to Immunotherapy in Epilepsy 2 (RITE2) scores (8 points), justifying the early initiation of methylprednisolone and intravenous immunoglobulin. Following intensive management and antibody confirmation in serum and cerebrospinal fluid tests, the patient achieved significant clinical improvement, seizure control, and successful tapering of antiseizure medications. This case emphasizes that AE is an important and potentially treatable cause of new-onset epilepsy in the elderly. Early recognition using validated clinical scales such as APE2 and RITE2 can support prompt immunotherapy and improve outcomes beyond antiseizure treatment alone.