High Dose Corticosteroid Therapy for Anti-Thymocyte Globulin Associated Severe Serum Sickness in an Adult Patient with Aplastic Anemia

C lassic serum sickness is a type III immune complex-mediated hypersensitivity disease caused by immunization of the host by non-human serum proteins [1] .Anti-thymocyte globulin (ATG) is one of the agents mostly responsible [2] .Steroids are mainly added to the treatment protocol of aplastic anemia (AA) in order to prevent ATG-associated serum sickness [3] . Case ReportIn March 2021, a 33-year-old female patient applied to our clinic with the complaint of fatigue with unremarkable personal medical history.Physical examination revealed pallor and vulvar erythema.The patient's hemoglobin level was 7.5 g/dl, white blood cell count was 1000/µl and platelet count was 5000/µl.The bone marrow cellularity was 10% and hereby the patient was diagnosed as very severe AA.Fluorescein-labeled proaerolysin test revealed 11% paroxysmal nocturnal hemoglobinuria clone at granulocytes.Diepoxybutane test was normal.Equine ATG (40 mg/kg/day for four days) and cyclosporine (5 mg/ kg/day to be added on the 14 th day) protocol was initiated as there was no readily available HLA (human leukocyte antigen)-matched sibling donor.Both epicutaneous and intradermal skin testing were performed before ATG administration.In order to prevent serum sickness, 2 mg/ kg/day intravenous methylprednisolone was applied.After four days of 40 mg/kg/day ATG administration, methylprednisolone dose was reduced to 1 mg/kg/day on the 5 th day.However, on the 8 th day of the treatment, the Classical serum sickness is a type III immune complex-mediated hypersensitivity disease caused by immunization of the host by non-human serum proteins.Anti-thymocyte globulin is one of the agents mostly responsible.Prophylactic steroids are used in the treatment protocol of aplastic anemia in addition to anti-thymocyte globulin.A 33-year-old female patient diagnosed with aplastic anemia developed severe serum sickness with anti-thymocyte globulin, despite the administration of a prophylactic dose of methylprednisolone.The patient responded dramatically to a single dose of pulse steroid therapy.There are reports that high-dose steroids (1-2 mg/kg/day to 500-1000 mg/day methylprednisolone) and/or therapeutic plasma exchange are beneficial treatment options.Our report shows the benefit of a single pulse dose of steroid and gradual tapering of the dose in this case.