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. These CD8⁺ T cells were found to be larger cells that stained positive for T-cell receptor Vβ13.6, and decreased shortly after steroid therapy. Our findings suggest that his acute encephalopathy was likely a clinical manifestation of HLH, and that immunophenotypic analysis may be helpful for early recognition of HLH in such rare encephalopathy.