Abstracts

RATIONALE:Midline spikes are uncommon compared to other scalp electrode locations. They have been reported to be most common in children, and are most frequently associated with complex partial or generalized tonic-clonic seizures. The aim of this study was to characterize the clinical and the EEG features of patients with midline spikes as the only epileptiform abnormality. METHODS:From the EEG database of the University of Michigan EEG laboratory, we identified 34 (17 male; 17 female) patients with midline spikes as their only epileptiform abnormality. Midline spikes were defined as focal epileptiform discharges localized to, or of highest amplitude at one of the vertex scalp electrodes Fz, Cz, or Pz. All EEGs were 21 channel recordings with scalp electrodes placed according to the 10-20 System. RESULTS:The spikes were localized or of highest amplitude at Cz in 19 (56%), at Fz in 8 (24%), Pz in 5 (15%) and equipotential at Fz and Cz in 2 (6%) patients. 41% of patients had additional non-epileptiform EEG abnormalities such as focal or generalized background slowing. Of the 18 patients with recording during both wakefulness and sleep, the latter led to an increase in spike frequency in 12 patients (67%). 86% of patients had a history of seizures, with onset before 5 years of age in 76%. 44% of the seizures were complex partial, 17% were secondarily generalized tonic-clonic, 11% were simple partial, 8% were myoclonic, 8% were generalized tonic, 6% were generalized tonic-clonic, 3% were atonic and 3% were gelastic. 29 patients had MRI scans which were normal in 70%. CONCLUSIONS:Midline spikes are most commonly maximum at the Cz electrode and are often activated by sleep. Patients with midline spikes commonly have an early age of onset of epilepsy, partial onset seizures and normal neuroimaging.