Misdiagnosis of sitosterolemia in a patient as Evans syndrome and familial hypercholesterolemia

Sitosterolemia is a rare form of dyslipidemia that has diverse clinical manifestations, and insufficient knowledge of the disease frequently leads to a delay in diagnosis. We report a case of sitosterolemia in a 26-year-old Chinese woman, characterized by anemia, thrombocytopenia, persistent hypercholesterolemia, premature atherosclerosis, extensive xanthoma, and arthralgia-tenosynovitis. Successive misdiagnoses of Evans syndrome and familial hypercholesterolemia had been made, and the patient had responded minimally to steroid therapy, splenectomy, and statin treatment; therefore, she was referred to our hospital. On admission, a peripheral blood smear revealed the presence of abnormally shaped erythrocytes and giant platelets. Multiple atherosclerotic lesions, sites of tenosynovitis, and carotid sheath xanthomas were identified on ultrasonography. Compound heterozygous mutations of the ABCG5 gene, including a hot variant (c.1,336, exon10 C>T, p.(R446*)) and a novel variant (c.1,325-3(IVS9)_c.1325-2(IVS9)delCA) were separately identified in her parents by pedigree analysis. Plant sterols analysis by high performance liquid chromatography method revealed remarkably elevated plasma plant sterol concentrations after drug withdrawal but reduced rapidly after restarting ezetimibe during follow-up period. After 21 months of treatment with ezetimibe and a low-plant sterol diet, her hematologic abnormalities, tenosynovitis, and hypercholesterolemia had significantly improved; and ultrasonography showed that her skin and carotid sheath xanthomas had resolved or shrunk. This case demonstrates that morphological changes in blood cells on a peripheral blood smear, ultrasonographic findings and ABCG5/ABCG8 gene screening are valuable, and plant sterol analysis in serum is crucial to confirm diagnosis and assess treatment adequacy for sitosterolemia.