Anti-SEZ6L2 antibody-associated autoimmune encephalitis initially misdiagnosed as cerebral infarction: a case report and narrative literature review

Anti-SEZ6L2 antibody-associated autoimmune encephalitis is a rare immune-mediated disorder characterized predominantly by progressive cerebellar ataxia. Due to its rarity and variable presentation, it remains under-recognized and is frequently misdiagnosed as cerebrovascular or neurodegenerative disease. We report a 53-year-old female who developed subacute dysarthria and progressive gait ataxia over several weeks in December 2024. Despite the absence of acute infarction on initial imaging, the presence of a patent foramen ovale (PFO) led to a presumptive diagnosis of embolic cerebral infarction at a local hospital. She received antiplatelet therapy and underwent PFO closure without clinical benefit. Upon transfer to our hospital, neurological examination revealed scanning speech, bilateral limb ataxia, mild left central facial weakness, positive bilateral Hoffmann signs, and a positive Romberg sign. Neurophysiology demonstrated brainstem and somatosensory pathway dysfunction. Serum and CSF anti-SEZ6L2 antibodies were positive (1:1000 and 1:100, respectively). The patient had a history of cervical carcinoma treated with surgery and chemoradiotherapy 11 years earlier, with no evidence of recurrence. She was treated with double-filtration plasmapheresis, mycophenolate mofetil, and rituximab, with stabilization of symptoms but residual deficits. We also conducted a narrative literature review and summarized the clinical features of 24 previously reported cases. This case illustrates that anti-SEZ6L2 antibody-associated encephalitis can be misdiagnosed as cerebral infarction, particularly when PFO is present. A careful history of symptom progression, absence of acute infarction on MRI, and lack of response to stroke therapy should prompt early autoimmune antibody testing. Diagnosis requires integration of clinical phenotype, antibody testing, and exclusion of alternative causes. Further studies are needed to establish standardized treatment protocols.