Prospective neurophysiological study in children treated for acute lymphoblastic leukaemia: Serial EEG during treatment and long-term follow up with evoked potentials

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Abstract
In 79 children treated for acute lymphoblastic leukaemia according to protocol ALL-BFM 81, serial EEG examinations were performed before, during and after therapy. Diffuse changes of the background activity were observed in 64% of the children at the time of diagnosis. During induction and reinduction treatment with vincristine andl-asparaginase, and with some delay after CNS irradiation, a marked slowing developed in up to 65% of patients. Children who had not been irradiated showed transient disturbances during treatment with medium-dose-methotrexate. Reinduction induced more abnormal EEGs in the children who had been irradiated. At the end of maintenance therapy, only slight EEG changes were found. No differences between the irradiated and non-irradiated group were then seen. Children with CNS leukaemia or seizures differed from those with an uncomplicated treatment in that they more often showed focal and persistent disturbances. In 39 patients who stayed in first remission for at least 18 months after the termination of treatment, a follow up investigation was performed. From the EEG examination, including power spectral analysis, no differences were found between irradiated and non-irradiated patients. Slowing of the dominant frequency was seen in the patients with more severe leukaemia and in those whose EEG had been markedly abnormal at diagnosis. The visually evoked potentials were normal in all groups of patients. In the brainstem auditory evoked potential, a prolongation of the latency of wave I and a decrease of the I–V interval was found in irradiated patients. We conclude that the diffuse EEG changes frequently emerging during treatment are reversible. Persistent or lateralized changes can indicate a neurological complication. Neurophysiological abnormalities found at long-term follow up, for the most part cannot be attributed to side-effects of the treatment but rather to disease related factors.