OBSOLETE: Sea-blue histiocytosis

Sea-blue histiocytosis (also known as sea-blue histiocyte syndrome) is a rare condition characterized by the accumulation of distinctive lipid-laden macrophages (histiocytes) in various organs, particularly the spleen, liver, and bone marrow. These histiocytes appear sea-blue or blue-green when stained and examined under a microscope, which gives the condition its name. The Orphanet entry for this condition is marked as OBSOLETE (Orphanet code 158029), meaning it is no longer classified as a distinct disease entity. This is because sea-blue histiocytosis is now generally recognized not as a single independent disorder but rather as a histopathological finding that can occur secondary to a variety of underlying conditions. Sea-blue histiocytes can be observed in the context of lipid storage disorders such as Niemann-Pick disease (particularly types B and C), as well as in conditions including chronic myeloid leukemia, myelodysplastic syndromes, hyperlipidemia, and other metabolic or hematologic disorders. When occurring as a primary (idiopathic) condition, patients may present with hepatosplenomegaly (enlargement of the liver and spleen), thrombocytopenia (low platelet count), and occasionally mild liver dysfunction or pulmonary involvement. Bone marrow examination typically reveals the characteristic sea-blue histiocytes. Because this entity is now considered obsolete as a standalone diagnosis, patients found to have sea-blue histiocytes are evaluated for underlying conditions that may be driving the accumulation. Treatment is directed at the underlying cause rather than the histiocytic finding itself. In cases previously classified as primary sea-blue histiocytosis, management has been largely supportive, addressing complications such as bleeding due to thrombocytopenia or organ enlargement. Splenectomy was historically performed in some cases with severe splenomegaly or significant cytopenias.

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