To report successful rituximab desensitization in two patients with refractory anti-muscle specific kinase (MuSK) myasthenia gravis (MG) and prior hypersensitivity reactions.

Rituximab, a monoclonal anti-CD20 antibody, has emerged as a preferred treatment in MuSK MG to improve clinical status and/or reduce the number or dose of immunosuppressive agents. Unfortunately, a conservative estimate of 20% of patients receiving rituximab for various indications may experience hypersensitivity/infusion reactions, which can limit its use.  

Two patients with refractory MuSK MG at our tertiary referral center had hypersensitivity reactions to rituximab. Patient 1 was a 29 year-old female, who reported hives on her face and throat closing. Patient 2, a 35 year-old female, had chest tightness. These symptoms were suspicious for IgE-mediated or mast cell activation reactions. The patients had limited therapeutic options outside of rituximab and required additional treatments. For subsequent rituximab infusions, they underwent intermediate desensitization protocols. The protocols were based on experience from the consulting Allergy team and published literature on rituximab desensitization mainly in patients with lymphoma. As part of the protocol, both patients were admitted to an intensive care unit and received an oral antihistamine on the morning of and 1 hour prior to rituximab infusion, as well as standard pre-medication with acetaminophen, antihistamines and steroids. Patient 2 was also pre-medicated with montelukast sodium and ipratropium bromide/albuterol sulfate. Rituximab dose and infusion rate were gradually increased over multiple steps. Patient 1 experienced subjective throat and scalp itching, which required rituximab to be stopped temporarily.  With additional intravenous diphenhydramine, she completed the infusion. Patient 2 tolerated the infusion without issues. 

Two patients with MuSK MG, who previously experienced IgE-mediated or mast cell activation reactions during rituximab infusions, successfully received subsequent infusions via an inpatient desensitization protocol. This process allowed them to continue rituximab treatment and maintain favorable disease control.