Electroencephalographic Evaluation for Early Diagnosis of Limbic Encephalitis

Limbic encephalitis (LE) is an inflammation of structures of limbic system. It may be an autoimmune disease or secondary to a neoplasia. Onset is subacute within a few weeks and clinical presentation is characterized by behavioral changes, psychiatric symptoms, short-term memory loss, and epileptic seizures. Diagnosis is typically set after a magnetic resonance imaging (MRI) scan, revealing hyperintensity in limbic structures on T2, fluid-attenuated inversion recovery (FLAIR), and diffusion-weighted imaging (DWI) sequences or detection of antineuronal antibodies; EEG aspecific alterations on temporal areas usually match with MRI and laboratory findings. Specific diagnostic criteria are still under debate. We describe a case presenting with EEG alterations before MRI ones.A 36-year-old woman came to our attention for a first generalized tonic-clonic seizure, several episodes of likely epigastric auras and memory loss. Her clinical history was unremarkable. Neurological examination and brain MRI with gadolinium were normal. Electroencephalographic (EEG) recordings showed theta activity and sharp elements in frontotemporal regions. Therapy with levetiracetam 1000 mg/day was started, but she had another generalized seizure and episodes of epigastric auras increased to 10 per day. After 2 months, another cerebral MRI revealed areas of swelling and signal alteration in deep left temporal areas, especially in hippocampal and parahippocampal gyrus. A spectroscopic evaluation revealed decreased N-acetyl aspartate peak and increased choline and myo-inositol peaks in left frontotemporal areas. These findings were consistent with LE. Cerebrospinal fluid (CSF) analysis was normal; viral serology and onconeuronal antibodies on CSF and blood were negative. Patient was treated with high-dosage steroids, with improvement in memory, epileptic seizures and auras. A third MRI revealed no signal alterations.In conclusion, the clinical picture initially did not meet accepted diagnostic criteria for LE. Effective steroid therapy was consequently delayed. With this case report we would emphasize diagnostic relevance of EEG alterations early in suspected LE in order to start immunosuppressive therapy as soon as possible.