[A case of lymphomatosis cerebri rapidly confirmed by brain biopsy].

Lymphomatosis cerebri (LC) is a variant of primary central nervous system lymphoma, which demonstrates diffuse white matter infiltrates without showing definite enhanced mass lesions on MR scans. We present a case of seventy-one year-old immunocompetent male who manifested with progressive truncal ataxia and drowsiness. The MRI exhibited diffuse white matter lesions from brainstem to cerebral hemispheres with minimum enhanced lesions at the first presentation. Because the diagnosis of LC was suspected, we performed a brain biopsy from the enhanced lesion near the right thalamus, which revealed diffuse large B cell lymphoma. After he underwent methylprednisolone pulse therapy and methotrexate chemotherapy, he obtained remission. Making a diagnosis of LC is often difficult because image findings resemble those of inflammatory or autoimmune diseases. LC is an important differential diagnosis to be considered in patients presenting with diffuse white matter disease. Performing a brain biopsy at the early phase is essential for the correct diagnosis and the favorable prognosis.