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Unusual radiographic presentation of methotrexate-induced leukoencephalopathy involving the internal capsule

© BMJ Publishing Group Limited 2022. No commercial reuse. See rights and permissions. Published by BMJ. DESCRIPTION A man in his early 20s with very highrisk Bcell acute lymphoblastic leukaemia on chemotherapy presented to emergency department (ED) as a strokecode activation for acute onset of focal neurological deficits of leftsided weakness and unsteady gait. He developed symptoms 2 hours prior to ED presentation. On examination, he had left lower facial weakness and left hemiparesis that was more pronounced in the distal musculature. He also had a widebased unsteady gait, positive Romberg and leftsided hyperreflexia. The patient received recent administration of intrathecal (IT) and intraventricular (IV) methotrexate 9 days prior as part of his treatment regimen. MRI performed in the ED less than 4 hours from symptom onset revealed an area of restricted diffusion in the posterior limb of the right internal capsule on diffusionweighted and apparent diffusion coefficient sequences without other areas of T2fluid attenuated inversion recovery (FLAIR) signal abnormality (figure 1) and normal MR angiography (not shown). The patient’s clinical presentation, MRI findings and recent history of administration of highdose IV and IT methotrexate was most suggestive of methotrexateinduced leukoencephalopathy. He was started on a cocktail treatment regimen of leucovorin, dextromethorphan, pyridoxine and folic acid with complete resolution within a few days and was discharged with a normal neurological examination. Strokes involving the internal capsule typically present with persistent symptoms of contralateral mixed sensorimotor deficits. However, in cases of methotrexateinduced leukoencephalopathy, symptoms are generally transient and selfresolve within a few days. In addition, T2 FLAIR lesions are not expected to appear on MRI in vascular strokes presenting less than a 6hour time frame from symptom onset. A pathognomonic feature of methotrexate toxicity is the appearance of both DWI and correlated T2 FLAIR lesion, as seen in our patient’s case. Neurotoxic effects of methotrexate and its radiological findings have been well established, especially in the young adult cancer population. Clinically, symptoms usually present within 2–14 days of methotrexate administration in acute onset methotrexate leukoencephalopathy. The typical radiologic findings of methotrexate toxicity in the brain are restrictive diffusion signals of a bilaterally asymmetric distribution crossing multiple vascular territories. However, unilateral and alternating lesions may also be seen. It can affect the centrum semiovale, with initial sparing of the subcortical U fibres. These lesions tend to be transient and disappear with symptom resolution. 2 Methotrexate is a folate antagonist and is a competitive inhibitor of dihydrofolate reductase in the folic acid cycle. In addition, certain neurotoxic metabolites accumulate such as adenosine in the cerebrospinal fluid (CSF) as well as homocysteine