High‐dose intravenous immunoglobulin to treat spontaneous heparin‐induced thrombocytopenia syndrome

Essentials Spontaneous HIT syndrome clinically/serologically resembles HIT but without proximate heparin. Rarely, spontaneous HIT syndrome complicates total knee arthroplasty surgery. Mesenteric vein thrombosis is a rare presentation of spontaneous HIT syndrome. IVIg rapidly corrects thrombocytopenia by inhibiting heparin‐independent platelet activation.Summary Spontaneous heparin‐induced thrombocytopenia ( HIT ) syndrome is an autoimmune HIT ( aHIT ) disorder characterized by thrombocytopenia, thrombosis, and HIT antibodies despite no proximate heparin exposure. For unknown reasons, many cases occur after total knee arthroplasty. A 52‐year‐old woman presented 12 days posttotal knee replacement (aspirin thromboprophylaxis) with gastrointestinal bleeding (superior mesenteric vein thrombosis); the platelet count was 63 × 10 9 L −1 . After bowel resection and a brief course of heparin, treatment was changed to argatroban followed by fondaparinux. In addition, high‐dose intravenous immunoglobulin ( IVI g), 1 g kg −1 on 2 consecutive days, resulted in abrupt platelet count rise from 21 (nadir) pre‐ IVI g to 137 (post‐ IVI g), and 2 days later to 200 × 10 9 L −1 . Heparin‐independent serum‐induced serotonin‐release abruptly decreased from 91% (pre‐ IVI g) to 14% (post‐ IVI g); although serotonin‐release later rebounded to 49%, the patient's platelet counts remained normal. Our observations support the emerging concept that high‐dose IVI g is effective for treating aHIT disorders, including spontaneous HIT syndrome.