5-FU multifocal inflammatory leukoencephalopathy and dihydropyrimidine dehydrogenase deficiency.

Multifocal inflammatory leukoencephalopathy (MIL) is a cerebral demyelinating syndrome that develops after chemotherapy with 5-fluorouracil (5-FU) and levamisole. The authors report a patient who developed MIL after 5-FU administration not in association with levamisole. She was subsequently diagnosed with partial deficiency of dihydropyrimidine dehydrogenase, an enzyme necessary for 5-FU catabolism. The authors suggest that MIL is a direct result of 5-FU chemotherapy and that patients with dihydropyrimidine dehydrogenase deficiency are at increased risk for this and other toxic effects of 5-FU.