A case of acute encephalopathy with hemophagocytic lymphohistiocytosis and clonal T-cell expansion.

We report on a 9-year-old boy who presented with acute encephalopathy and hemophagocytic lymphohistiocytosis (HLH). The patient was referred to our hospital because of fever, seizures, and decreased consciousness. He showed moderately elevated levels of proinflammatory cytokines in the cerebrospinal fluid and plasma, and clonal expansion of highly activated CD8⁺ T cells in the peripheral blood.