Long-term neurological implications of somnolence syndrome in children with acute lymphocytic leukemia.

A longitudinal study of 49 children with acute lymphocytic leukemia (ALL) assessed the long-term effects of central nervous system (CNS) prophylaxis on brain function. From 10 to 12 electroencephalograms (EEGs) were done before and at intervals during after 30 months of treatment that included 2,400 rads of CNS irradiation plus intrathecal methotrexate therapy. None of the children had CNS leukemia, and all remained in first complete remissions. All 49 had abnormally slow EEG background frequencies during the four-year study, and 29 (60%) developed somnolence syndrome six to eight weeks after CNS prophylaxis. During this syndrome, EEG background frequencies decreased more than 3 standard deviations below the expected mean values for normal children. Thereafter, 7 of the 29 began to show signs of learning disabilities and 7 developed recurrent seizures. Of the 20 children who did not have the syndrome, none showed later evidence of CNS dysfunction. Somnolence may be an early indicator of long-term neurological sequelae after cranial irradiation.