Diagnostic Significance of Paraneoplastic Neuronal Antibodies in Japanese Adults with Autoimmune Encephalitis: A Case Series Study in an Adult Epilepsy Clinic.

Purpose: Recently, the role of autoimmune mechanisms in epileptogenesis and intractability has attracted attention. The clinical features of autoimmune encephalitis (AE) vary; thus, diagnosis can be difficult and often delayed. Paraneoplastic neurological syndromes are usually associated with malignant cancers; however, paraneoplastic antibodies (PAs) can be present in the absence of overt cancers. In this single-center, retrospective study, we evaluated the diagnostic significance of PAs in adult Japanese patients with AE.

Patients and methods: We retrospectively analyzed the medical records of all patients who visited our epilepsy clinic and underwent a thorough diagnostic evaluation for AE between April 2021 and October 2022. Patients who met the criteria for AE and presented to our epilepsy clinic with new-onset seizures or acute or subacute seizure aggravation were included. Data from the PA panel, including anti-amphiphysin (AMPH), CV2, paraneoplastic Ma antigen 2 (PNMA2), Ri, Yo, Hu, recoverin, SRY-related HMG-box gene 1 (SOX1), titin, zic4, glutamate decarboxylase 65 (GAD65), and Tr/DNER antibodies, were evaluated.

Results: Of 32 patients who were investigated, 6 (19.0%; 2 males, age: 38.0 ± 18.0 years) were positive for PAs (anti-AMPH: 1, PNMA2: 1, Yo: 1, recoverin: 2, SOX1: 1). No patients had malignant tumors. Serum anti-SS-A/Ro antibodies were detected in one patient, and the cerebrospinal fluid showed a slightly elevated protein level. Intravenous high-dose methylprednisolone was administered to four patients and was effective in three.

Conclusion: Approximately one-fifth of AE cases were attributable to PAs, although there were no signs of malignant tumors, in adult epilepsy clinics in Japan.