Magnetoencephalographic analysis of periodic lateralized epileptiform discharges (PLEDs)

Objective: To clarify the spatial and temporal distribution of the electroencephalographic (EEG) pattern termed ‘periodic lateralized epileptiform discharges’ (PLEDs), we performed magnetoencephalography (MEG) to analyze PLEDs in a patient with a right parietal metastasis associated with meningeal carcinomatosis. Methods: A 37-channel biomagnetometer was used to simultaneously record the EEG and MEG. Equivalent current dipole (ECD) source localization was calculated based on a single-dipole model and mapped onto a magnetic resonance image. Single-photon emission computed tomography with technetium-99-hexamethyl-propyleneamine oxime (HMPAO-SPECT study) was also performed during both presence and absence of PLEDs according to an EEG monitor. Results: By EEG the PLEDs, predominantly right-sided, consisted of a typical negative triphasic spike followed by a slow negative wave. By MEG the PLEDs had a sequence with 3 distinct components. ECDs in the 3 components were localized to the cortex around the lesion, although exact localization and dipole direction varied between components. HMPAO-SPECT demonstrated hypoperfusion of the lesion and adjacent cortex during both quiescence and appearance of PLEDs. Conclusion: Our results indicate that PLEDs originated from the hypoperfused cortex surrounding the lesion.