The frequency, clinical characteristics and outcome of children with isolated midline spikes in the EEG, and comparison of those with and without epilepsy, were analyzed by researchers at Children’s Hospital, Boston, MA. In a total of 12,000 EEGs performed from 2005 to 2009, 69 had Cz-Pz discharges as the only epileptiform abnormality. Midline spikes were defined as focal epileptiform discharges localized to or of highest amplitude at one of the vertex scalp electrodes, Cz or Pz. Midline spikes were differentiated from transient vertex waves of sleep by their occurrence during the awake stage as well as sleep. EEGs with discharges at additional sites were excluded. The prevalence of isolated midline spikes was 0.54%; 45 (65%) were in boys. Median age was 6 years (range, 4 mo -23 yrs); 2-3 yr-olds were the most common age group (16 cases), followed by the 4-5 yr-olds (11 cases). Forty-three (62%) had a history of seizures, and 26 (37%) without epilepsy presented with symptoms suggestive of seizures. In the group with seizures, Cz and Pz spikes occurred in 33% (14 of 43 cases); Cz spikes only in 49% (21 of 43 cases), and Pz spikes only in 18% (8 of 43 cases). Seizures were partial in 25 (58%); complex partial in 22 (51%), and focal myoclonic in 3. MRI was abnormal in 56% cases with seizures, and 26% of those without (P<0.05). The group with seizures was 5 times more likely to develop new discharges at additional sites than the nonepilepsy group. In the nonepilepsy group, 46% had developmental delay, 19% pervasive developmental disorder, and 15% had ADHD; these disorders were significantly more frequent in the nonseizure group than in those with seizures (P<0.05). Computerized source analysis in 12 random cases showed that isolated midline spikes were localized to the midline convexity, similar to the EEG localization by surface electrodes. 
COMMENT. The authors conclude that isolated midline spikes do not invariably signify an increased susceptibility to seizures, but also occur in normal children and in children with developmental and behavioral problems. A repeat EEG in a child with midline spikes and epilepsy is more likely to show new discharges in additional sites.