Rituximab, a chimeric anti-CD20 monoclonal antibody, is used to treat rheumatologic and hematologic
diseases. Serum sickness, a Type III delayed hypersensitivity reaction, has been reported with rituximab treatment.
Traditionally, drug desensitization has been used to treat Type I IgE-mediated hypersensitivity reactions. We report the
first case of successful drug desensitization to rituximab in a patient with medication-induced serum sickness. In our case,
a 37-year-old woman with Sjogren’s syndrome and papillary thyroid carcinoma developed serum sickness 72 hours
following rituximab infusion for gastric mucosal associated lymphoma tissue (MALT). Her MALT progressed after
stopping rituximab. She underwent a rapid 12-step intravenous rituximab desensitization without recurrence of serum
sickness. Following the completion of 4 rituximab desensitizations, she had gastric MALT remission. She received 25
maintenance rituximab doses using this desensitization protocol quarterly without complications. This is the first report
documenting rituximab desensitization for the treatment of delayed drug reactions like serum sickness.
Keywords: Desensitization, hypersensitivity, mucosa associated lymphoid tissue, rituximab, serum sickness.
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