18F-FDG Superscan Caused by Extensive Bone Marrow Involvement in Hemophagocytic Lymphohistiocytosis.

An 82-year-old woman who initially presented with pulmonary infection had persistent pancytopenia, which presented a diagnostic dilemma requiring multiple bone marrow biopsies for eventual diagnosis of hemophagocytic lymphohistiocytosis. This case highlights the utility of FDG PET in (a) focusing attention on the bone marrow and reticuloendothelial system as the primary site of pathology and (b) excluding underlying malignancy and infection in this rare but potentially fatal hyperinflammatory condition caused by a highly stimulated but ineffective immune response.