Methotrexate-induced neurotoxicity (MTX-Ntox) is a frequent complication of methotrexate (MTX) therapy for patients with both malignant and inflammatory diseases. MTX-Ntox can occur after intrathecal MTX or after low-, intermediate-, or high-dose systemic administration. Symptoms can present in the acute, subacute, or late setting form, and can range from affective disorders, malaise, and headaches, to somnolence, focal neurologic deficits, and seizures. While the pathogenesis of MTX-Ntox is likely multifactorial, one potential biochemical pathway leading from MTX to neurotoxicity involves the folate dependent remethylation of homocysteine (Hcy). MTX therapy is known to cause elevations of both plasma and CSF Hcy. Hcy is directly toxic to vascular endothelium and it and its metabolites are excitatory agonists of the N-methyl-D-aspartate (NMDA) receptor. Competitive or noncompetitive antagonists might afford protection from or reversal of MTX-Ntox. Using high-performance liquid chromatography (HPLC) with coulometric electrochemical detection, the authors measured CSF Hcy in sequential patients with severe subacute MTX-Ntox. CSF Hcy was higher in these patients (n = 9, median = 0.93 microM) than in asymptomatic patients (n = 11, median 0.2 microM, p < .01). Five patients with severe subacute MTX-Ntox (most with dysarthria and/or hemiplegia) were treated with 1-2 mg/kg oral dextromethorphan (DM), a noncompetitive antagonist of the N-methyl-1-aspartate (NMDA) receptor. All five had resolution of symptoms. These data provide additional clinical support for elevated CSF Hcy in the induction of MTX-Ntox through activation of the NMDA-receptor. These data provide support for a placebo-controlled clinical trial to examine the ability of DM to prevent or alleviate MTX-Ntox.

To the Editor Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasm of childhood with nearly half of all patients relapsing within 3 years [1,2]. More than 90% of JMML patients present with initiating mutations in NF1, KRAS, NRAS, RRAS, RRAS2, CBL, and PTPN11, all leading to hyperactivation of the Ras pathway [3]. Patients with additional molecular alterations including cytogenetic abnormalities, and in particular, point mutations in SETBP1 have inferior outcomes [4]. At present, hematopoietic stem cell transplantation (HSCT) is the only curative therapy, with the primary cause of death being relapse or progression to acute myeloid leukemia (AML) [5]. Recently, JMML patients who did not display Ras pathway mutations were found to have ALK and ROS1 fusions that were sensitive to ALK inhibition [6]. Given the poor overall survival of JMML patients even after intensive treatments such as HSCT, opportunities to implement precision medicine should be

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