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Abstract

Abstract Background Anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) encephalitis is an autoimmune encephalitis with a wide range of clinical manifestations. Underlying conditions should be evaluated on a case-by-case basis, and the pathophysiology of fulminant anti-AMPAR encephalitis remains incompletely understood, with very few opportunities for pathological investigation. Case presentation An 84-year-old woman developed disorientation to date and place 7 days before admission and was admitted with a fever of 39 °C. On hospital day 3, she developed a decreased level of consciousness, with a Glasgow Coma Scale score of 8, along with tremor and rigidity of the limbs. Brain magnetic resonance imaging revealed bilaterally symmetric lesions in the frontal and temporal cortices and subcortical regions, basal ganglia, and limbic system. Cerebrospinal fluid analysis showed an elevated interleukin-6 level of 3,940 ng/L. Immunotherapy consisting of intravenous methylprednisolone pulse, plasma exchange, and intravenous immunoglobulin was administered for suspected autoimmune encephalitis. Although the cerebrospinal fluid interleukin-6 level decreased to 16.3 ng/L, impaired consciousness did not improve, and cerebral atrophy was observed. Subsequently, high-titer AMPAR antibodies were detected in the cerebrospinal fluid. However, the patient died on hospital day 39 from septic shock. Autopsy revealed infiltration of CD8-positive T cells, microglial accumulation, proliferation of reactive astrocytes, and neuronal loss in the hippocampus. No malignant tumors were identified. Conclusions Among cases of fulminant AMPAR encephalitis, some may exhibit severe inflammation associated with markedly elevated cerebrospinal fluid interleukin-6 levels and prominent CD8-positive T-cell infiltration. Longitudinal assessment of cerebrospinal fluid interleukin-6 levels should be considered to better characterize the disease course.