Rituximab is a treatment option for patients with Lambert–Eaton myasthenic syndrome (LEMS) who do not respond to standard immunosuppressive therapy.
How rituximab works
LEMS is an autoimmune condition in which the immune cells (T and B-cells) mistakenly attack the neuromuscular junction — the point where nerve cells meet muscles. The attack blocks the communication between nerve cells and muscles, causing the symptoms of LEMS.
Rituximab is a monoclonal antibody that binds to a specific protein — CD20– present on the surface of B-cells. This binding triggers the lysis (disintegration) of B-cells, thereby decreasing their number in the blood and dampening their attack on the neuromuscular junction.
As a therapy for autoimmune conditions like LEMS, rituximab may have another mechanism of action. One of the functions of B-cells is to introduce the T-cells to their target to prime them for an immune attack. By reducing the level of B-cells, rituximab also may disrupt this function and prevent T- cells from attacking the target, which in the case of LEMS is the neuromuscular junction.
Rituximab research
Rituximab is prescribed for LEMS treatment based on its function to suppress the growth of B-cells. However, it has not been assessed in clinical trials involving LEMS patients, but its effectiveness has been described in LEMS patients who were prescribed rituximab by their healthcare team.
A reassessment of medical data from LEMS patients who were treated with rituximab highlighted its effectiveness as a therapeutic option for LEMS. In this study, researchers from the U.K. collected data from 10 patients with myasthenia gravis, a neuromuscular condition related to LEMS, and two patients with LEMS who underwent rituximab treatment. In 18 months, three patients (25%) achieved remission, while five (42%) showed clinically relevant improvements. Rituximab treatment alleviated symptoms in both LEMS patients, and both showed improvement during follow-up.
A case report of a 61-year-old man with LEMS who lacked muscle coordination, causing walking difficulty (gait ataxia), speech difficulty (dysarthria), and swallowing problems (dysphagia), was published in the journal Muscle & Nerve. Standard immunosuppressive treatment with azathioprine did not improve his condition, so doctors switched to rituximab, administered twice with a two-week interval between each infusion. Rituximab treatment led to a marked decrease in B-cell counts and an alleviation of symptoms after two courses of treatment. After 12 months, the B-cells increased in number again, but when the patient was given two more doses of rituximab at two-week intervals, this led to the depletion of B-cells and clinically relevant improvement in his condition. Rituximab’s effect was maintained even at the five-year follow-up.
Other information
Rituximab was initially developed as a cancer therapy. It is now a treatment approved by the U.S. Food and Drug Administration (FDA) under the brand name Rituxan for six conditions. These include two types of cancer (non-Hodgkin’s lymphoma and chronic lymphocytic leukemia), two inflammatory conditions (granulomatosis with polyangiitis and microscopic polyangiitis), and two autoimmune disorders (rheumatoid arthritis and pemphigus vulgaris).
Last updated: July 24, 2019
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