[A case of late-onset SLE complicated with EDTA-dependent pseudothrombocytopenia]

A 57-year-old man was admitted to our clinic with complaints of proximal myalgia in extremities. He was diagnosed as late-onset SLE based on the findings of pleuritis, pericarditis, arthritis and antibodies to DNA and cardiolipin. Aggregation of the platelets and the decreased counts of platelets were observed when EDTA was used as anticoagulant for the blood tests. However, the platelet aggregation was not noted with normal counts of platelets when Heparin-Theophylline was used as anticoagulant. From this observation, EDTA-dependent pseudothrombocytopenia was diagnosed and IgM class of EDTA-dependent anti-platelet antibody was detected by means of flow cytometry. Administration of prednisolone at 40mg/day reduced the symptoms and EDTA-dependent pseudothrombocytopenia, and EDTA-dependent anti-platelet antibody disappeared. His clinical course suggested that EDTA-dependent pseudothrombocytopenia was closely associated with the disease activity of SLE.