A possible case of serum sickness after ocrelizumab infusion.

A 41-year-old female diagnosed with multiple sclerosis began ocrelizumab treatment. She received her first treatment course without significant complication. After receiving the first maintenance dose 6 months later, she developed weakness, myalgias, gastrointestinal symptoms, headache, and intermittent fever persisting for 4 weeks. A working diagnosis of serum sickness was determined after excluding other probable entities. She received 3 days of 1 g methylprednisolone intravenously and five plasma exchanges, experiencing gradual improvement. Serum sickness has occurred with monoclonal antibodies including rituximab. This case of possible ocrelizumab-associated serum sickness suggests that clinicians should remain vigilant about this possibility with this medication.