Methotrexate(MTX) Induced Leukoencephalopathy(LE) and Relation of Vitamin B12, Folate and / or Homocysteine Levels with MTX Toxicity: A Prospective Study

Background: MTX-induced neurotoxicity is often associated with leukoencephalopathy, and the diagnostic radiological feature in magnetic resonance imaging (MRI) is white matter hyper intensities. The clinical significance of these white matter changes is unknown. The risk factors of MTX-induced acute leukoencephalopathy are not well established. Few authors have suggested increased homocysteine or alteration of Central Nervous System (CNS) folate, vitamin b12 homeostasis may be associated with CNS toxicity. It is a usual clinical practice to withhold methotrexate during further duration of chemotherapy after an episode of leukoencephalopathy but the risk of neurotoxicity must be weighed against the risk of relapse of leukemia. Moreover, there is limited data on continued treatment with High-dose methotrexate (HD-MTX) or Intrathecal Methotrexate (IT-MTX) or Oral-MTX in patients who developed leukoencephalopathy.

Objective: The study aims to 1) identify the risk and prevalence of leukoencephalopathy in patients of Acute Lymphoblastic Leukemia (ALL) receiving intrathecal or high dose or oral methotrexate therapy through sequential MRI Brain study. 2) Safety of re-administration of methotrexate in patients with documented toxic leukoencephalopathy 3) The relationship of serum homocysteine, vitamin b12 and folate levels with methotrexate induced leukoencephalopathy

Methods: Our study enrolled 34 newly diagnosed pediatric ALL / Lymphoblastic Lymphoma (LBL) patients (age ≤18 years) between June 2019 & June 2020. Induction chemotherapy was initiated as per modified ALL IC BFM 2002 protocol after obtaining informed consent. Apart from the Hematological investigations, Bone Marrow Aspiration and Biopsy, Flow Cytometry/Immunohistochemistry (IHC), Cytogenetics, Molecular study were done. All the patients underwent MRI Brain and Serum homocysteine, Vitamin B12, Folate level measurement (sequentially as per protocol at 4 different time points). 1st time point - AT DIAGNOSIS, i.e. before starting methotrexate, 2nd time point - POST CONSOLIDATION, 3rd time point - POST EXTRACOMPARTMENT THERAPY, 4th time point - IN MAINTENANCE, thus analyzing leukoencephalopathy secondary to different modes of administration of methotrexate therapy. At all-time points serum folate, vitamin b12 or homocysteine level were done before administering methotrexate and any association with development of leukoencephalopathy was analyzed.

Results: We identified Leukoencephalopathy secondary to methotrexate in 6.03% (7/116) on MRI brain in 5 of 33 (15.15%) patients of which 1 (3.03%) had symptomatic LE and 4 (12.12%) were clinically asymptomatic. All our LE patients were in the age group more than or equal to 10 years. We found no increase in the incidence of leukoencephalopathy secondary to methotrexate: leucovorin ratio, also there was no difference in the incidence with respect to mode of administration of MTX (IT/HD/ORAL), even there was no increase in incidence after 4 courses of high dose methotrexate. MRI at baseline was not a predictor of development of leukoencephalopathy. 3 out of 5 patients with LE had abnormal b12/folate/homocysteine with corresponding abnormal MRI Brain at pre-specified time point. Also 4 patients with abnormal b12/folate/homocysteine levels had intractable cytopenias while on chemotherapy and more after HD MTX therapy which got corrected after supplementation with vitamin b12 and folic acid.

Conclusion: MTX-induced clinical leukoencephalopathy is transient, and most patients can be re-challenged with subsequent MTX without recurrence of acute or subacute symptoms. MRI at baseline was not a predictor of development of leukoencephalopathy. More multi institutional prospective studies of large number of patients are needed to study the incidence of MTX-induced leukoencephalopathy and its relation with folic acid, vitamin b12 and homocysteine level.