The case of a 10-year-old immunocompetent male who initially presented with fatigue and ataxia following a viral illness, and MRI findings compatible with acute disseminated encephalomyelitis (ADEM), and who later was diagnosed with systemic lymphoma is reported from Children’s Memorial Hospital, Chicago, Illinois. Brain MRI showed white matter signal abnormalities in frontal and parietal lobes, the right temporal lobe, and in the basal ganglia, cerebral peduncles, and left brachium pontis. CSF contained 7 white cells/mcL, protein 28 mg/dL, glucose 68 mg/dL, and negative cytology. Ataxia and fatigue improved following treatment with a 5-day course of methylprednisolone 20 mg/kg/day, and the MRI showed resolution of the lesions. An acute exacerbation of the fatigue and ataxia occurring within 1 month was unresponsive to IV immunoglobulin, and the patient was referred for a second opinion. Examination revealed a horizontal nystagmus, and left hemiplegia, left axillary lymphadenopathy, and halo nevi on the back. The white blood cell count was 2.5 x 103/mcL, serum lactate dehydrogenase 944 IU/L, and serum neopterin 58 (normal <10 nmol/L). CSF showed 12 wbc/mcL, protein 196 mg/dL, and glucose 66 mg/dL. MRI revealed new areas of abnormal signal in the right caudate head, basal ganglia, and internal capsule. T-cell lymphoma was diagnosed by supraclavicular lymph node biopsy, and confirmed by stereotaxic biopsy of the right caudate. Chemotherapy and radiotherapy resulted in significant resolution of the tumor on MRI, but the patient died of overwhelming bacterial sepsis. 
COMMENT. The diagnosis of lymphoma should be considered in cases of ADEM that recur, deteriorate, or are accompanied by lymphadenopathy, halo nevi, elevated neopterin, lymphopenia, and elevated lactate dehydrogenase. The initial presentation in this case was typical for acute disseminated encephalomyelitis. The dramatic neurologic decline was unlike an ADEM recurrence, and the lymphadenopathy and laboratory findings led to the final diagnosis of occult systemic T-cell lymphoma.
Cognitive outcome after treatment for primary CNS lymphoma is evaluated in a cohort of 19 patients who were in complete remission after treatment with IV and intrathecal methotrexate followed by whole brain radiotherapy . Cognition was impaired in 12 (63%) patients despite a complete tumor response, and the degree of impairment correlated with age. White matter abnormalities and cortical atrophy occurred in 14, and cortical atrophy correlated with cognitive functioning and age. The neurocognitive decline is multifactorial, including the disease itself, age-related comorbidity, and the toxicity of treatment . The tumor infiltrates beyond the margins of the tumor bulk and may resemble encephalitis. The median age at diagnosis is 60 years, and many patients have other pathology. The risk of neurotoxicity with treatment increases with patient age, and chemotherapy and radiation have a synergistic toxic effect, especially when radiation precedes chemotherapy.