[Primary central nervous system lymphoma: a case report and evaluation of the diagnostic value of IL-10 level in the cerebrospinal fluid].

We report a case of primary central nervous system lymphoma (PCNSL) that presented with visual disturbance. A 76-year-old man developed decreased bilateral visual acuity. He was diagnosed with bilateral retrobulbar neuritis by an ophthalmologist. Treatment with high-dose corticosteroids was initiated and resulted in mild improvement of visual acuity. However, the patient gradually became apathetic and bradykinetic, experiencing difficulty performing the activities of daily living; he was admitted to our hospital because of this progressive illness. Neurological examination revealed bradyphrenia and bradykinesia with frontal lobe release signs, disorientation, and ideomotor apraxia. Magnetic resonance imaging showed abnormal signals in the bilateral basal ganglia and thalamus. Cerebrospinal fluid (CSF) examination revealed no pleocytosis and slightly elevated protein levels: β2-microglobulin level was mildly increased, and IL-10 level in the CSF was markedly elevated. These findings suggested a diagnosis of PCNSL, and a brain biopsy specimen was obtained from the left caudate head. Pathological findings indicated diffuse large B-cell lymphoma. Nonspecific neurological manifestations and radiological findings can make the diagnosis of PCNSL difficult and result in delayed diagnosis. Visual impairment has been suggested as a feature of PCNSL, and an elevated IL-10 level in the CSF may be a useful marker for diagnosing PCNSL.