Rituximab seen as safe, effective in treating MuSK-positive MG
Analysis found fewer symptoms, stable disease in majority of patients
Rituximab can safely and effectively control myasthenia gravis (MG) in patients with antibodies against muscle-specific kinase or MuSK, according to a new analysis.
“Rituximab has demonstrated effectiveness and safety as a treatment for anti-MuSK MG. It has the potential to help patients with any baseline severity, especially those with mild to moderate disease, achieve [a state of minimal manifestations] or better. Additionally, rituximab reduces the required maintenance dose of prednisolone,” a corticosteroid, the researchers wrote.
Findings from the analysis were detailed in the study, “Efficacy and safety of rituximab in anti-MuSK myasthenia Gravis: a systematic review and meta-analysis,” published in Scientific Reports.
Rituximab is used off-label in MG, other autoimmune diseases driven by B-cells
An autoimmune disease, MG is caused by antibodies that interfere with the communication between nerve and muscle cells, leading to disease symptoms of muscle weakness and fatigue. In a minority of patients, MG-driving antibodies specifically target a protein called MuSK.
Rituximab, sold as Rituxan and biosimilars, is an antibody-based therapy that works to lower the number of B-cells, the immune cells that produce antibodies. It was originally developed to treat B-cell cancers, but in recent years it has been increasingly used off-label to help manage autoimmune diseases like MG that are driven by B-cells.
“Despite emerging evidence, comprehensive data regarding rituximab dosage, efficacy, and safety in anti-MuSK MG patients are still lacking,” the researchers wrote.
This led scientists in Thailand to conduct a systematic review and meta-analysis into the effects of rituximab in MG patients with anti-MuSK antibodies. A meta-analysis is a technique where researchers pool data from multiple studies and analyze their findings collectively.
This work included data from 12 studies covering 111 adults with anti-MuSK MG who were treated with rituximab. Responses to treatment were evaluated using a standardized tool called the MG Foundation of America Postintervention Status (MGFA-PIS).
Majority of 95 patients went into stable remission with rituximab
Results showed that, as of the latest follow-up, 82% of the 111 patients achieved a state of minimal manifestations or better on the MGFA-PIS — essentially meaning they had few symptoms, or none at all. Additionally, more than half (56%) of the 95 rituximab-treated patients who were evaluated for pharmacological or complete and stable remission met that criteria as of the latest follow-up. Essentially, this finding means these people had no notable symptoms while still being on some form of therapy (pharmacological remission), or in the absence of treatment (complete stable remission).
The proportion of patients responding to rituximab was similar among those with more severe MG and those with mild to moderate disease.
“These results suggest that rituximab offers similar benefits across different severities and can be initiated at any stage of the disease,” the researchers wrote.
Rituximab also led to notable reductions in the dosage of corticosteroids, which dropped by a mean of 17.15 mg, the researchers noted. Corticosteroids are anti-inflammatory medications that are commonly used to help manage MG, though high doses taken for long periods of time can cause a series of side effects.
Common side effects reported to be mild, but longer studies needed
Rituximab was generally well tolerated. The most common side effects were mild and included malaise (a general feeling of being sick), flushing in the face, and skin rash. One patient experienced osteomyelitis, a type of bone infection, that was considered a serious side effect.
Researchers noted that most of the studies included in this meta-analysis were fairly short in duration and observational rather than randomized and controlled clinical trials. As such, more work is needed to assess the long-term safety and efficacy of rituximab in anti-MuSK MG.
“Future studies with extended observation periods and standardized monitoring of [antibody] levels and infection rates are essential to fully assess the long-term benefit-risk profile of rituximab in anti-MuSK MG,” they wrote.
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