Management of CNS Involvement in Pediatric ALL

Rationale for Intrathecal Chemotherapy

The National Comprehensive Cancer Network recommends CNS-directed therapy with intrathecal chemotherapy as the cornerstone of treatment because systemic chemotherapy cannot adequately penetrate the blood-brain barrier to clear leukemic cells from the CNS 1, 2, 3
CNS involvement is classified based on the presence of lymphoblasts in the CSF, requiring specific CNS-directed treatment, with the goal of clearing leukemic cells from the CNS 1, 2, 3

Anticonvulsants may be needed for symptomatic management of seizures, but they do not address the underlying leukemic infiltration of the CNS, and convulsions are a symptom of CNS leukemia, not the primary problem requiring treatment 1, 2
Systemic chemotherapy alone cannot adequately cross the blood-brain barrier to achieve therapeutic concentrations in the CSF, and the aim of CNS treatment is to clear leukemic cells from sites that cannot be readily accessed by systemic chemotherapy due to the blood-brain barrier 1, 2, 3
A VP shunt addresses hydrocephalus but does not treat leukemic cells in the CSF, and there is no indication for VP shunt placement in the management of CNS leukemia 1, 2

The National Comprehensive Cancer Network states that all patients with ALL require CNS prophylaxis, as over 50% would develop CNS leukemia without CNS-directed therapy, and the complete approach includes intrathecal chemotherapy, high-dose systemic chemotherapy with CNS penetration, and cranial radiation in specific cases 1, 2, 3
Intrathecal chemotherapy is the primary modality, and high-dose systemic chemotherapy with CNS penetration, such as methotrexate, cytarabine, and pegaspargase/calaspargase, is also used 1, 2, 3
Cranial radiation is reserved for specific protocols and CNS-3 disease, but is increasingly avoided due to late neurotoxic effects 1, 2, 3

The National Comprehensive Cancer Network recommends not delaying intrathecal therapy while waiting for systemic chemotherapy to take effect, as the blood-brain barrier prevents adequate systemic drug penetration, and CNS disease will progress 1, 2, 3

The American Society of Clinical Oncology and other guidelines recommend transfusing platelets to achieve a count >50,000/μL before performing lumbar puncture with intrathecal chemotherapy, as this is the minimum safe threshold for therapeutic anticoagulation and invasive procedures in cancer patients with thrombocytopenia 4
For patients with platelet counts between 20,000-50,000/μL, the risk of bleeding with invasive procedures is significantly elevated, and half-dose anticoagulation is the maximum recommended 4
The National Comprehensive Cancer Network recommends that lumbar puncture, if performed, be done concomitantly with initial intrathecal therapy rather than as a separate diagnostic procedure 5, 6

The ASCO/CAP/ASH guidelines provide a strong recommendation that for patients with ALL receiving intrathecal therapy, the treating clinician should obtain a CSF sample with cell count and blast enumeration 7, 8, 9, 10
Ensure cell count is performed with examination and enumeration of blasts on cytocentrifuge preparation reviewed by pathologist 7, 8, 9, 10
Flow cytometry should be used in CSF evaluation for superior sensitivity over conventional cytology, particularly for detecting low levels of CNS infiltration 7, 11

Monitor platelet counts closely during chemotherapy, as severe thrombocytopenia (<20,000/μL) requires holding therapeutic anticoagulation 4
Consider prophylactic platelet transfusions before scheduled intrathecal chemotherapy sessions 4