Abstracts

Rationale: Vertex waves of sleep often lateralize to the left or right frontocentral regions but can be mistaken for epileptiform discharges, especially when they are completely lateralized. This pitfall of electroencephalogram (EEG) interpretation may relate to the lack of information about this topic. The aim of this study is to assess the prevalence and significance of completely lateralized vertex waves of sleep in pediatric patients with and without epilepsy. We hypothesized that completely lateralized vertex waves are a normal phenomenon and occur with a similar prevalence in patients with and without epilepsy. Methods: We conducted a retrospective, blinded, case-control study evaluating completely lateralized vertex waves in 100 pediatric patients with a diagnosis of epilepsy and compared these findings to 100 age and gender-matched patients without epilepsy. Cases and controls were randomly selected from an EEG database. Cases were diagnosed with epilepsy and controls were patients who had an EEG obtained for spells but did not receive a diagnosis of epilepsy. At least three years had passed since the EEG to allow sufficient time for clarification of the diagnosis. Patients with an abnormal brain MRI were excluded. A five minute sleep epoch (beginning with the first definite vertex wave of sleep) was independently reviewed by both authors using a longitudinal bipolar montage. Although vertex waves often lateralize to some degree, we chose to study only completely lateralized vertex waves (maximal at the midline with a field to the left or right frontocentral region - see Figure) to improve objectivity. Results: Data is presented in Table. Completely lateralized vertex waves occurred in 62% of patients with epilepsy and in 65% without epilepsy (p=0.66). In those with completely lateralized vertex waves, the median number per five minutes of sleep was three in those with epilepsy and four in those without epilepsy (p=0.11). The percentage of patients with at least two vertex waves completely lateralized to only one hemisphere was identical between groups (14%). Within cases, the number of patients with completely lateralized vertex waves was similar in those with focal (54%) and generalized epilepsy (66%; p=0.24). The number of cases with multiple, completely lateralized vertex waves to one hemisphere only was identical between the focal and generalized epilepsy subgroups (14%). Conclusions: This is the first systematic study of the prevalence and significance of completely lateralized vertex waves of sleep. This study provides Class III evidence that completely lateralized vertex waves are a normal phenomenon and should not be confused with epileptiform discharges.