EEG and magnetic resonance imaging abnormalities in patients with acute limbic encephalitis

Abstract

OBJECTIVE: To describe the characteristics of electroencephalography (EEG) and MRI in patients with acute limbic encephalitis (LE). PATIENTS AND METHODS: We retrospectively reviewed medical records of 57 patients with diagnosis of LE from May 1994 to April 2010 and selected those with available EEG and MRI records. We analyzed EEG characteristics (type of abnormality, location and periodicity), reviewed MRIs and compared both. RESULTS: We included 22 patients, age ranging from 3 months to 71 years. EEG was abnormal in 21 patients (95.5%): Periodic lateralized epileptiform discharges (PLEDs) in 9 patients (40.9%), epileptiform discharges and/or temporal slow waves in 7 (31.8%) and 5 (22.7 %) with only background slowing. MRI showed abnormalities in temporal lobes of 19 patients (86.4%). The presence of PLEDs was strongly associated with hyperintense MRI-FLAIR signal involving hippocampus and temporal lobe cortex. Bilateral periodic lateralized epileptiform discharges (Bi-PLEDs) seen in two patients were related to extensive symmetrical bitemporal hyperintense MRI-FLAIR signal. Three patients with PLEDs had only mild ipsilateral FLAIR-hyperintense abnormalities, while contralateral temporal areas were moderate to severely affected on MRI. In four patients with smaller asymmetric bilateral lesions we observed PLEDs in the most affected side. Diffuse slow waves were observed in three patients with discrete hyperintense signal on MRI. CONCLUSION: PLEDs are a typical EEG finding in LE, but not present in all cases. However EEG may predict the extension of MRI abnormalities: slow, mild and nonspecific EEG abnormalities may be related to discrete MRI lesions, while PLEDs to extensive lesions. Moreover, in bilateral, asymmetrical and widespread lesions PLEDS may be contralateral to the most affected ("burned-out") area on MRI.