Electroencephalographic Evaluation for Early Diagnosis of Limbic Encephalitis

Abstract

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.

CSF in acute and chronic infectious diseases

“…Specific EEG features can however give clues as to the diagnosis: In HSE, in addition to background slowing, there is a temporary temporal focus showing periodic epileptiform discharges. The EEG in subacute sclerosing panencephalitis (SSPE) shows a typical generalized periodic EEG pattern repeating with intervals between 4 and 15 seconds and synchronized with myoclonus of the patient (Westmoreland, 1987;Gaspard et al, 2015;Martins and Palmini, 2015;Cag et al, 2016;Pessa et al, 2016;Saini et al, 2016). Due to the strong separation of blood and brain by the blood-brain barrier, the peripheral blood results in viral meningitis and encephalitis can be normal or only slightly abnormal and nonspecific.…”

Differences in epileptic symptoms depending on the type of autoimmune-mediated limbic encephalitis

“…The emergence of this phenomenon is associated with a more prolonged illness [57]. Pessa et al [104] reported a case of autoimmune-mediated LE whose EEG changes preceded the radiological changes; therefore, we should consider the diagnostic value of early EEG changes in autoimmune-mediated LE, which may be helpful for early therapy and the improvement of prognosis.…”

Autoimmune Limbic Encephalitis – literature review

“…• Electroencephalography (EEG): EEG may show signs of inflammation in the temporal lobe area, such as slow waves and epileptiform discharges. These changes, even when the MRI image is normal, allow us to suspect ALE and should prompt further diagnostics and repeat MRI in order to assess the possible progression of changes over time [33]. However, in some patients with ALE, the EEG examination may be normal [34].…”