Serum Sickness Reaction to Rituximab with Positive Immediate Intradermal Skin Test: A Case Report

Background: Rituximab is a chimeric murine/human monoclonal antibody against CD20. It can be used off-label in autoimmune diseases. Its administration can lead to several types of reactions; immediate infusional reactions and also delayed reactions like Serum Sickness Reaction (SSR). Case presentation: This is a case study of a 48 years old woman diagnosed with rheumatoid arthritis/systemic lupus erythematosus who developed refractory immune thrombocytopenic purpura and received treatment with rituximab. After treatment, she developed erythematous-violet lesions accompanied with fever of 38ºC, dyspnea, joints arthralgia and edema. In the emergency department, hypotension, fever, dyspnea, and shivering were observed, for which, intramuscular epinephrine, intravenous corticosteroids, antibiotics and salbutamol nebulization were administered. In our allergy unit, we performed an intradermal test (IDT) with rituximab (1mg/ml), which was positive at immediate (20min) and late (48h) reading. Based on the clinical manifestations and test carried out, she was diagnosed with rituximab SSR. We also studied the molecular mass of the IgE-reactive proteins present in rituximab product by SDS-PAGE Immunoblotting method according to Laemmli, in reducing and non-reducing conditions, with high sensitivity and using three different polyvinylidene difluoride (PVDF) membrane blocking substances (skimmed cow's milk, fish collagen and egg white). We did not detect IgE-binding to rituximab product. Conclusion: The pathogenesis of SSR is not well known. The patients after reinfusion can develop immediate reactions suggesting involvement of IgE hypersensitivity. Nevertheless, there are patients who tolerated reinfusion. Further studies and assays are needed for a better understanding of these reactions and to lead to a safer re-administration if needed.