Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disease that mainly affects muscles in the lower limbs. It is named after Edward Lambert and Lee Eaton, neurologists at the Mayo Clinic in Rochester, Minnesota, who described the syndrome in the 1950s and ’60s.
How LEMS affects the body
LEMS is characterized by muscle weakness that starts in the lower limbs, making walking and climbing stairs more difficult. As the disease progresses, the arms and shoulders are also affected and everyday tasks can become a challenge.
LEMS can also cause problems with speech, chewing, and swallowing. A weakening of the eye muscles can lead to double vision and eyelid drooping.
Most patients also have signs of autonomic (involuntary) nervous system dysfunction, such as dry mouth and eyes, constipation, little sweating, and impotence.
What causes LEMS?
LEMS is an autoimmune disease, a disorder in which the immune system attacks the body’s own tissues. More specifically, immune cells target calcium channels in the nerve cell endings that control muscle movement. Calcium channels are involved in the release of the neurotransmitter acetylcholine, a chemical messenger that triggers muscle contraction. When the levels of acetylcholine are too low for proper muscle contraction, the result is muscle weakness.
There are two forms of LEMS. One form is associated with small-cell lung cancer and accounts for about 50–60% of cases. The calcium channels that are attacked by the immune system are also present on the surface of the cancer cells. It is thought that the antibodies generated to fight cancer cells mistakenly attack the calcium channels on nerve cells.
In people without small-cell lung cancer, the disease’s cause is not well-understood, but there likely is a genetic association.
How is LEMS diagnosed?
The extent of muscle weakness is assessed during a physical exam, as are tendon reflexes because they are often poorer in people with LEMS.
Electromyography (EMG) is performed to determine muscle-nerve cell interaction.
The presence of antibodies against calcium channels is highly specific for the condition, and detectable in about 85% of LEMS patients. They are found in patients with and without small-cell lung cancer.
People without this cancer who are positive for calcium channel antibodies will likely undergo a chest CT scan to look for tumors in the lung.
How is LEMS treated?
The treatment of LEMS depends on whether or not it is associated with cancer. This is because cancer treatment is a priority, and usually leads to an easing of LEMS symptoms.
Firdapse (amifampridine) is a U.S. Food and Drug Administration (FDA)-approved medication for the relief of LEMS symptoms. It is a potassium channel blocker that increases the calcium influx into the nerve endings, stimulating the release of acetylcholine.
Cholinesterase inhibitors such as pyridostigmine block the enzyme that breaks down acetylcholine (cholinesterase), so that acetylcholine is around longer.
Immunosuppressive medications such as prednisone can help control immune system attacks; it suppresses the production of autoantibodies by specific immune cells.
Plasmapheresis is a procedure that filters the blood to remove harmful antibodies, and can help relieve LEMS symptoms.
Intravenous immunoglobin (IVIG) replacement therapy involves the injection of nonspecific antibodies (immunoglobins) from donated blood, which are thought to inhibit the immune system’s production of autoantibodies.
Last updated: August 1, 2019
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