Why Should I Be Tested for Cancer if Diagnosed with LEMS?
If you have been diagnosed with Lambert-Eaton myasthenic syndrome (LEMS), a rare autoimmune disease that, among its symptoms, causes muscle weakness, it’s very important you be screened for cancer as soon as possible.
Around 60% of LEMS cases are associated with small cell lung cancer (SCLC), a very aggressive type of lung cancer, and LEMS onset can precede a finding of this cancer, especially among older patients.
How do doctors diagnose LEMS?
Diagnosing LEMS is a multi-step process. A physical exam in people complaining of problems with walking, climbing stairs, or lifting things generally reveals a weakness in muscles of the legs and arms. Doctors typically ask the person to next undergo a type of muscle test, called an EMG, that measures electrical impulses the brain sends to the muscles via nerve cells. Weakness in these signals can be an indicator of LEMS.
Doctors then perform a blood test to determine whether patients are producing autoantibodies against their own voltage-gated calcium channels (VGCC), proteins present at the neuromuscular junction — the point where nerve cells meet muscle cells. These antibodies decrease the nerve signals that the muscles can receive, slowing the muscle response. Over time, this can cause muscles to weaken and atrophy.
What’s the connection between LEMS and SCLC?
Cancer cells often produce proteins that healthy cells don’t. SCLC cells can produce VGCC, which is normally only present at the neuromuscular junction. In attempting to fight these cancer cells, the immune system generates antibodies against this protein.
However, these antibodies also attack the healthy neuromuscular junction, causing muscle weakness and the other symptoms of LEMS.
The presence of these autoantibodies can be an indication of cancer, but a LEMS diagnosis is not a definitive sign of cancer.
Small cell lung cancer is most often found in males diagnosed with LEMS at older ages, with a history of tobacco smoking.
LEMS and other cancers
An association between LEMS and other types of cancers is found in about 10% of cases. It’s not clear why, other than the possibility that these tumors are causing an immune system reaction much in the same way as SCLC.
Last updated: May 18, 2020
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