Methotrexate-induced acute toxic leukoencephalopathy.

Acute lymphoblastic leukemia (ALL) is one of the most common malignancies of childhood, which is treated with high doses of methotrexate (MTX), as it crosses the blood-brain barrier and can be administered intravenously and via intrathecal route to eradicate leukemic cells from central nervous system (CNS). Additionally, high doses of MTX not only prevent CNS recurrence but also hematologic relapses. Although, standard treatment protocol for ALL includes multimodality therapy, MTX is usually associated with neurotoxicity and affects periventricular deep white matter region. Methotrexate-induced 'acute toxic leukoencephalopathy' has varying clinical manifestations ranging from acute neurological deficit to seizures or encephalopathy. Diffusion weighted magnetic resonance imaging (DW-MRI) is widely available and routinely used in clinical practice to identify acute stroke and also to distinguish acute stroke from non-stroke like conditions. We report a local teenage Chinese girl who developed 2 discrete episodes of left upper and lower limb weakness with left facial nerve paresis after receiving the 2 nd and 3 rd cycle of high dose of intravenous and intrathecal methotrexate, without having cranial irradiation. After each episode of her neurological deficit, the DW-MRI scan showed focal restricted diffusion in right centrum semiovale. Her left sided focal neurological deficit and facial nerve paresis almost completely subsided on both these occasions within 3 days of symptom onset. Follow-up DW-MRI, after her neurological recovery, revealed almost complete resolution of previously noted restricted diffusion in right centrum semiovale, while the lesion was not evident on concurrent T2W (T2-weighted) and FLAIR (Fluid-Attenuated Inversion recovery) sequences, nor showed any post contrast enhancement on post gadolinium enhanced T1W (T1-weighted) sequences. No residual neurological deficit or intellectual impairment was identified on clinical follow up over a 2 year period.