Figure 2. Electroencephalogram (EEG) at the time of presentation in the neurology clinic (A) and 3 months later (B). The initial EEG (A) reveals periodic bursts of high-amplitude, slow-wave complexes. (Onset of the complexes is indicated by solid arrows; offset, by open arrows.) The background rhythm is normal, except for bifrontal slowing. This "burst-suppression" pattern is highly characteristic of subacute sclerosing panencephalitis (4). EEG 3 months later, when the patient's clinical status has worsened (B), again shows periodic high-amplitude slow waves (again, between the solid and open arrows), but they now arise from a diffusely slowed background rhythm, which nearly obscures the periodic slow waves. In both A and B, the interval between each vertical dotted line is one second.