Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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May 2, 2016
Acute Methotrexate-Induced Encephalopathy
- Background:
- Acute methotrexate-induced leukoencephalopathy is the most common form of treatment-related acute neurotoxicity in children with hematologic malignancies.
- Clinical Presentation:
- Stroke-like events, confusion, tremor, and epilepsy. Symptoms appear between 6 hours and 11 days after chemotherapy administration
- Key Diagnostic Features:
- Well-defined area of restricted diffusion with mild hyperintensity on T2-FLAIR in the subcortical white matter sparing the U fibers
- Exact pathophysiology is unknown. The most admitted hypothesis is a reversible metabolic encephalopathy leading to cytotoxic edema in cerebral white matter.
- Recent studies show genetic predisposition.
- Differential Diagnosis: Other causes of restricted diffusion
- Pyogenic abscess: "Double rim sign" on T2WI (hypointense outer and hyperintense inner rim). Rims are significantly more hypointense on T2*-weighted imaging. Pyogenic abcesses are usually surrounded by vasogenic edema.
- Neoplasm (lymphoma or glioblastoma): There is associated enhancement. Glioblastomas usually do not restrict as strongly, are surrounded by vasogenic edema, and have increased rCBV. Lymphomas are usually deep-seated (periventricular white matter, corpus callosum, thalami, and basal ganglia), hyperdense to normal brain on NECT scans, may show microhemorrages on T2*-weighted imaging, and show minimal fall in signal intensity and characteristic rapid signal overshooting above the baseline on MR perfusion.
- Viral encephalitis: Diffusion restriction may be associated with transient splenial lesion of the corpus callosum. Basal ganglia, thalami cortex usually involved.
- Venous infarct: Direct or indirect signs of venous thrombosis, eg, filling defect of a venous sinus in time-of-flight MR venography. Focal swelling of the parenchyma and usually no or mild restricted diffusion.
- Postictal state: Restricted diffusion usually concerns the cortex, hippocampus, and splenium of the corpus callosum.
- Treatment:
- Deficits usually resolve completely and spontaneously after methotrexate is stopped. Coma and death are rare.
- Folate and vitamin B12 are often added (deficiency worsens symptoms).
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