A 6 year-old girl presented with progressive weakness and sensory loss in both legs for three weeks. She had a recent history of acute lymphocytic leukemia treated with chemotherapy.

Nerve root enhancement can be seen in a variety of inflammatory and infiltrative disorders, including Guillain Barré syndrome and chronic inflammatory demyelinating polyneuropathy. Subsequent CSF evaluation of this patient demonstrated leukemic cells. Without a known primary tumor, the diagnosis of infiltration of the nerve roots from metastatic tumor can be very difficult to make. Even when the tumor cells are adherent to the nerve roots, CSF cytology often shows only a reactive lymphocytosis without frank tumor cells. In some cases, nerve root biopsy is necessary.