Approved Treatments for LEMS
Lambert-Eaton myasthenic syndrome (LEMS) is a rare disease in which the immune system mistakenly attacks a protein on the nerve endings, resulting in muscle weakness and other symptoms. There is currently no cure for LEMS, but there are treatments to manage symptoms and improve patients’ quality of life. Scroll down to learn more about some of the ways LEMS can be treated.
Firdapse (amifampridine) is the first and only oral treatment approved in the U.S. for the symptomatic treatment of LEMS patients age 17 and older. It is a small molecule therapy designed to restore the acetylcholine that is required for the transmission of nerve signals to the muscles, thereby improving muscle function in people with LEMS.
Guanidine is a small molecule oral medication that has been used to treat the symptoms of LEMS, although, due severe side effects, it is not the preferred treatment for the disorder. Guanadine may improve muscle function by binding to potassium channels and prolonging the nerve signal. This facilitates the absorption of calcium by the remaining healthy calcium channels.
In LEMS, muscles weaken and atrophy as the immune system attacks the nerve cell endings, weakening nerve signals. Cholinesterase inhibitors block the enzyme that breaks down acetylcholine, meaning that a stronger, longer-lasting nerve signal can be sent. These medications are prescribed off-label for LEMS, with pyridostigmine the most commonly used.
Medications known as immunosuppressants can be used in autoimmune diseases such as LEMS to reduce the severity of symptoms. LEMS is caused by the body’s immune system mistakenly attacking the nerve cell endings, leading to the destruction of calcium channels that release the neurotransmitter, or cell-signaling molecule, acetylcholine. Immunosuppressants work by suppressing the activity of the immune system so that the autoimmune attack on the nerve cell endings is reduced.
Azathioprine is used to prevent organ rejection following a transplant and to treat certain autoimmune conditions. If symptoms are not sufficiently controlled by first-line treatment with Firdapse, patients may receive long-term treatment with the immunosuppressive medications prednisone and azathioprine.
Mycophenolate is an oral medication that dampens immune system reactions by blocking the function of inosine monophosphate dehydrogenase. Another mechanism of action described for mycophenolate is the disintegration of activated T-cells, which are immune cells programmed to attack a particular target, like nerve cell endings in the case of LEMS.
Prednisone is a man-made corticosteroid used in the treatment of LEMS. It acts in a similar way to the corticosteroid hormones synthesized by the outer layer of the adrenal glands, such as cortisol. Prednisone has anti-immune and anti-inflammatory effects; it suppresses the production of autoantibodies by immune system cells called B-cells, thereby alleviating LEMS symptoms.
Rituximab is a treatment option for patients with LEMS who do not respond to standard immunosuppressive therapy. Rituximab is a monoclonal antibody that binds to a specific protein — CD20 — present on the surface of B-cells. This binding triggers the disintegration of B-cells, thereby decreasing their number in the blood and dampening their attack on the neuromuscular junction.
Other treatments that may be beneficial for LEMS patients include IVIG replacement therapy and plasmapheresis. Both procedures are designed to combat the presence of autoantibodies in the blood to ease disease symptoms. These treatments provide only temporary relief and need to be repeated regularly.
IVIG Replacement Therapy
Intravenous immunoglobulin (IVIG) replacement therapy is approved in the U.S. to treat patients with compromised immune systems. The therapy also can be used to treat LEMS. IVIG is a component prepared from human blood. Using donor blood, antibodies of a particular type — immunoglobulins — are isolated and purified of potential contaminants, such as other blood components. This mixture of antibodies is injected directly into the bloodstream of a LEMS patient.
Plasmapheresis, or plasma exchange, is a treatment commonly used in autoimmune diseases to remove circulating harmful antibodies — known as autoantibodies — that mistakenly recognize the body’s own proteins as foreign. It is generally used to stabilize LEMS patients and restore the normal signaling between the nerve cells and the muscle cells at the neuromuscular junctions. That, in turn, improves muscle contraction.