Case Report: Coexistence of Anti-AMPA Receptor Encephalitis and Positive Biomarkers of Alzheimer's Disease

Anti–α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor encephalitis is a rare autoimmune disease that is characterized by acute cognitive impairment, mental symptoms, and seizures. The high comorbidity rate between anti–AMPA receptor (AMPAR) encephalitis and other somatic diseases, such as malignancy, has revealed the possibility of potential copathogenesis. However, there have not yet been reports about anti-AMPAR encephalitis with concomitant cerebrospinal fluid (CSF) biomarkers consistent with Alzheimer disease (AD). Herein, we present the case of an elderly male patient with autoimmune encephalitis (AE) presenting with anti–AMPA1-R and anti–AMPA2-R antibodies, as well as CSF biomarkers of AD. The patient was hospitalized with acute memory decline for 1 week. Anti–AMPA1-R and anti–AMPA2-R antibodies were positively detected in CSF, and the anti–AMPA2-R antibody was also present in the serum. Additionally, the biomarkers of AD were concurrently present in CSF (Aβ(1−42) = 245.70 pg/mL, t-Tau = 894.48 pg/mL, p-Tau = 78.66 pg/mL). After administering a combined treatment of intravenous immunoglobulin and glucocorticoids, the patient recovered significantly, and his cognitive function achieved a sustained remission during 2 months' follow-up. This case raises the awareness of a possible interaction between AE and changes of CSF biomarkers. We speculated that the existence of AMPAR antibodies can induce changes of CSF, and other pathological alterations. This present report highlights that a potential relationship exists among AE and provides a warning when making the diagnosis of AD.