Purpose: To describe the incidence of acute neurotoxicity (NT) in children with lower risk B-precursor acute lymphoid leukemia (ALL) treated with intermediate-dose methotrexate (MTX) or divided dose oral MTX with or without intravenous (i.v.) mercaptopurine (MP) and extended intrathecal triple therapy.

Patients and methods: Thirteen hundred four patients were entered onto Pediatric Oncology Group (POG) 9005, a randomized phase III trial, between January 11, 1991 and September 1, 1994. After remission induction, patients were randomized to one of three 24-week intensification schedules: regimen A, MTX 1,000 mg/m2 i.v. infused over 24 hours and MP 1,000 mg/m2 i.v. infused over 6 hours; regimen B, low-dose repetitive MTX 30 mg/m2 orally every 6 hours for six doses and i.v. MP; or regimen C, i.v. MTX alone. Intensification was given every 2 weeks for 12 courses. CNS prophylaxis was age-adjusted intrathecal MTX (ITM). In August 1992, the CNS prophylaxis was changed to age-adjusted triple intrathecal therapy (TIT). Reports of grades 3 and 4 acute NT were reviewed.

Results: Acute NT was reported in 95 of 1,218 (7.8%) eligible patients treated on POG 9005. The incidence by regimen was regimen A, 46 of 543 patients (8.3%); regimen B, 13 of 354 patients (3.7%); and regimen C, 36 of 321 patients (11.2%) (P < .001). The majority of events were seizures and the median number of days to first occurrence of symptomatic NT after ITM or TIT was 10 to 11 days. Computed tomography (CT) or magnetic resonance imaging (MRI) evidence consistent with leukoencephalopathy (LE), with or without the presence of cerebral calcifications, was observed in 75% and 77.1 % of symptomatic patients treated on regimens A and C, respectively, but in only 15.4% of symptomatic patients treated on regimen B (P < .001). Factors associated with an increased incidence of NT included increased cumulative exposure with repeated i.v. MTX (regimens A and C v B), increased MTX-leucovorin (LCV) ratio (regimens A and C v B), and choice and timing of TIT therapy. The use of i.v. MP during intensification did not appear to contribute to these complications. The switch to TIT CNS prophylaxis was associated with an inferior overall 4-year continuous complete remission (CCR) (P=.031) when compared with ITM.

Conclusion: Intensification with repeated i.v. MTX in the setting of low-dose LCV rescue was associated with a higher risk for acute NT and LE, especially in patients who received concomitant TIT. The long-term consequences for affected patients remain unknown.