Nocturnal frontal lobe epilepsy

Nocturnal frontal lobe epilepsy (NFLE) is a condition primarily characterized by seizures occurring exclusively or predominantly during sleep, the semiology of which suggest a frontal lobe origin and, more specifically, the involvement of the orbitofrontal or mesial frontal regions. It is usually considered as a relatively benign and homogeneous epileptic syndrome, the neuropsychological impact of which should be minimal. However, several issues complicate this view. 1. NFLE is rather a heterogeneous disorder which includes both sporadic and familial forms, various seizure types, and drug resistance in about 30% of patients. 2. The frontal origin of seizures has rarely been demonstrated, and mainly relies on the presence of ictal signs suggestive of frontal lobe epilepsy, but which might only reflect the propagation of ictal discharges of extrafrontal origin. 3. NFLE-like seizures were recently found to be associated with temporobasal cortical dysplasia, or an insular epileptogenic zone, including one patient with autosomal dominant frontal lobe epilepsy (ADNFLE). 4. No study has yet specifically evaluated the neuropsychological profile of patients with NFLE. Available data suggest that behavioral problems and mental retardation might be associated with ADNFLE, especially when it is related to a mutation of the nicotinic receptor subunits. Conversely, the majority of NFLE patients does not seem to present with gross cognitive disturbance, even though many of these patients complain of chronically disrupted sleep and daytime sleepiness. Further research is warranted in this field, keeping in mind that the neural networks underlying NFLE remain poorly known and might primarily involve extrafrontal brain regions in some patients.