Rett syndrome and the electroencephalogram.

The EEG is almost always abnormal in patients with Rett syndrome. This is demonstrated in a study based upon 230 EEG records obtained from 44 patients. Rhythmical slowing (mostly 3-5/sec) represents the most common EEG abnormality (30 patients). Diffuse, scattered or bilateral-synchronous spikes or sharp waves were found in 22 patients. Slow spike-wave complexes were present in 9 patients. With advancing age, the EEG abnormalities tend to decline and ill-defined low voltage records may develop. These changes may parallel an intrinsic disease course with an early active phase followed by a phase of residual impairment.