Electroencephalography features of primary epileptogenic regions in surgically treated MRI-negative infantile spasms

To evaluate the surgical outcome for intractable, MRI-negative infantile spasms (IS), and to identify diagnostic targets in the focal epileptogenic area by methods other than MRI.

We retrospectively studied 9 patients who had had surgery for intractable IS, and whose lesions did not appear on MRI. We analyzed video/electroencephalography (EEG), single photon emission computed tomography (SPECT) and positron emission tomography (PET) findings and their surgical outcomes. In 7 patients who were seizure free after surgery, we analyzed the EEG parameters for characteristics expected in the primary epileptogenic region.

All patients underwent resective surgery including frontal lobectomy and multilobar resection. Seven patients showed an Engel class I outcome, and 2 patients showed a class III outcome. Interictal SPECT results showed 66.7% concordance for the hemisphere affected (lateralization), and 55.6% for lesion location (localization). Ictal SPECT showed 71.4% concordance for lateralization and localization. PET showed 66.7% concordance for lateralization, and 55.6% for localization. EEG parameters, including localized paroxysmal fast activities, spindle-shaped fast activities, repetitive or rhythmic sharp/spike wave discharges, and subclinical seizures showed highly localized specificity, and may serve to identify the epileptogenic lesion.

Surgical treatment of MRI-negative IS should be justified using a combination of diagnostic methods.