Rituximab is effective in treating myasthenia gravis (MG), especially in patients with antibodies to muscle-specific kinase (MuSK), however, may increase the risk of severe infections, according to a study published in Neuromuscular Disorders.

During the study, all 12 patients with anti-MuSK antibodies achieved minimal manifestation status (MMS) or remission, but only 33% (6/18) of patients with antibodies against acetylcholine receptors (AChR) achieved similar success. After 1 year of follow-up, 11 of the 12 anti-MuSK patients and 3 of the 6 anti-AChR patients remained in MMS or remission.

Nine severe infections were observed in 5 of the patients, all of whom were anti-AChR positive. The infections included pneumonia (n=4), gastrointestinal infection (n=2), cytomegalovirus (n=1), methicillin-resistant Staphylococcus aureus (MRSA; n=1), and progressive multifocal leukoencephalopathy (PML; n=1). 

Read more about MG prognosis

Two of the patients died from their infections, one with MRSA and the other with PML. A third patient is suspected of having PML and is currently being treated with periodic plasma exchange without any other immunosuppressants.

Of the 5 patients who developed an infection, 3 had hypogammaglobulinemia with immunoglobulin G (IgG) levels <7 g/L. Hypogammaglobulinemia was also observed in 33% (7/21) of patients who did not develop an infection.

In general, mean IgG levels dropped as the study progressed, with levels of 10.7 g/L at baseline, 9.1 g/L at 3 to 15 months after treatment, and 8.5 g/L at 24 to 48 months post-treatment with rituximab. Patients who developed infections had lower IgG levels in general before and after treatment with rituximab: 8.2 vs 11.2 g/L at baseline (P =.03); 5.8 g/L vs 9.4 g/L at 3 to 15 months (P =.03); and 5.9 vs 8.9 at 24 to 48 months (P =.036).

“Our data confirm previous reports showing that rituximab is highly effective in patients with MG, especially those with anti-MuSK antibodies. However, we observed a relatively non-negligible infection rate after administration of rituximab, potentially due to low IgG levels,” the authors said.

Reference

Caballero-Ávila M, Álvarez-Velasco R, Moga E, et al. Rituximab in myasthenia gravis: efficacy, associated infections and risk of induced hypogammaglobulinemia. Neuromuscul Disord. Published online June 21, 2022. doi:10.1016/j.nmd.2022.06.006