Long-term electro-clinical changes in the Lennox-Gastaut syndrome before, during, and after the slow spike-wave pattern.

Patients (64) with the Lennox-Gastaut Syndrome (LGS) were followed with EEGs (602) and clinical findings over a 42 yr period, up to 51 yrs of age. Before the slow spike-wave (SSW) complex appeared, in over one half of the patients focal discharges were seen and most often (71%) many discharges were noted, all associated with generalized seizures. With the SSW, two thirds of the patients showed additional focal discharges, again most often (72%) very many or many were noted. Clinical attacks were usually generalized but partial attacks also were seen. Although the largest absolute number of SSW complexes appeared in young children, the highest percentage of recordings with SSW was found between 25-29.9 yrs. Changes in the frequency of the spike-wave complexes were occasionally noted, not only decreasing in frequency from 3-6/sec down to 1-2/sec, but also increasing up to 3-6/sec. After the disappearance of the SSW in time, focal discharges, diffuse and focal slow waves were seen in nearly all records and complex partial seizures increased in number. This study has emphasized the importance of the cortex in the LGS and also the instability of the pattern that occasionally appears.