Focal abnormalities in idiopathic generalized epilepsy: A critical review of the literature

Conventionally, epilepsy is dichotomized into distinct "focal" and "generalized" categories. However, many studies have reported so-called focal features among patients with idiopathic generalized epilepsy (IGE) in the domains of semiology, electroencephalography, neuropsychology, neuropathology, and neuroimaging. We sought to review such features and clinical implications. A Web of Science database search was conducted to identify relevant publications. Our search yielded 145 papers describing focal features involving different domains in IGE, with 117 papers analyzed after excluding abstracts and case reports. Focal semiologic features are commonly seen in IGE. There are conflicting data from studies in the domains of electroencephalography, neuroimaging, and neuropathology. Studies on neuropsychology are suggestive of frontal lobe functional deficits in juvenile myoclonic epilepsy. Most advanced neuroimaging studies demonstrate the involvement of both the thalamus and the cortex during generalized spike-wave discharges (GSWDs). A few electroencephalographic and neuroimaging studies indicate that the cortex precedes the thalamus at the onset of GSWD. Focal features may contribute to misdiagnosis of IGE as focal epilepsy. However there are methodologic limitations in the studies that affect the results.