SUN-698 - Sea Blue Histiocytosis: Beyond A Histopathologic Finding - A Case Report

Sea blue histiocytosis (SBH) is a rare histopathologic finding that affects histiocytes in any hematopoietic organ, most commonly the spleen and bone marrow (1). The histiocytes appear blue-green on Wright–Giemsa staining due to the accumulation of phospholipids and glycosphingolipids (2). SBH can result from mutations in the apolipoprotein E (APOE) gene, leading to lipid accumulation in a syndrome known as inherited lipemic splenomegaly (3). SBH has also been described in lipid storage disorders, autoimmune diseases such as autoimmune neutropenia and immune thrombocytopenia (4), myeloproliferative disorders (5), and other conditions.
Our patient is a 41-year-old woman with a medical history significant for type 2 diabetes mellitus, hypertriglyceridemia, morbid obesity, hepatic steatosis, and hypertension who was referred to endocrinology for hypertriglyceridemia in the setting of SBH. The patient had undergone splenectomy one year earlier for progressive symptomatic splenomegaly. Subsequent spleen pathology demonstrated sea blue histiocytosis. The patient had no history of autoimmune disease, bariatric surgery, or total parenteral nutrition use. Her lipid panel at evaluation showed a total cholesterol level of 176 mg/dL (reference range: < 200 mg/dL) and triglycerides of 171 mg/dL (reference range: < 150 mg/dL). She was referred to hematology and underwent bone marrow biopsy, flow cytometry, karyotype analysis, and molecular testing, none of which showed evidence of myeloproliferative or myelodysplastic disease. Her rheumatologic workup was unremarkable. The patient was also referred to genetic medicine and underwent a screening panel for lipid storage disorders, which was unrevealing. Whole-exome sequencing identified a mutation in the intraflagellar transport protein complex (IFT140) gene, which is associated with polycystic kidney disease (PKD); however, no APOE gene mutations were detected.
This case highlights the significant gaps that remain in the understanding of SBH. Although this finding may be associated with inherited lipemic splenomegaly, particularly in isolated splenic involvement, this association is not the rule. The differential diagnosis is broad, and neoplastic and non-neoplastic conditions must be carefully excluded (1). SBH may also be associated with hypertriglyceridemia (1); however, our patient had only mild hypertriglyceridemia, for which lifestyle modifications were recommended. A review suggests an association between SBH and thrombocytopenia (6); however, our patient did not have thrombocytopenia and instead developed mild thrombocytosis, likely reactive to splenectomy. One report describes a patient with lupus nephritis and bone marrow SBH deposition (7). Ultimately, SBH remains a rare finding, but recognition of this entity is important for clinicians to ensure appropriate diagnostic evaluation and timely referral.

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