It is sometimes caused bysmall-cell lung cancers, but other times has no apparent trigger.
The term myasthenic just means muscle weakness.
Instead, they generally begin slowly and gradually worsen with time.
Verywell / Katie Kerpel
Fatigue and muscle weakness are key symptoms of LEMS.
The fatigue may be intense and worse after exercise.
The muscle weakness usually first affects the muscles of the upper legs.
This leads to problems with climbing stairs or getting oneself up out of a deep chair.
Weakness of the upper arms usually comes next.
Eventually, the weakness may spread to the lower arms and legs and eventually to the hands and feet.
These might include:
Some people with LEMS also have symptoms related to their eyes.
These might includedrooping eyelidsor double vision.
LEMS also sometimes causes difficulty swallowing or speaking.
However, these symptoms tend to be mild and temporary, if present.
Causes
LEMS occurs because of problems at an area called the neuromuscular junction.
Normally, a signal from the brain sends a message through this neuron to move the muscle.
To send this signal, the neuron receives a nerve signal that causes some calcium channels to open.
This causes some calcium ions to rush inside the neuron.
This, in turn, triggers the release of certain signaling molecules, called neurotransmitters.
These neurotransmitters are taken up by the nearby muscle cells, and they cause it to tighten.
In LEMS, antibodies to these calcium channels are produced.
Because of this, fewer of these channels can work properly.
That means that less neurotransmitter signal to the muscle can be released.
Sometimes antibodies to the other parts of the neuromuscular junction are present as well.
Because of all this, the involved muscle doesnt contract as well.
That leads to the symptoms of LEMS.
This can happen from a punch in of lung cancer known as small-cell lung cancer.
Smoking is by far the most important risk factor for developing small-cell lung cancer.
However, most people with small-cell lung cancer never get symptoms from LEMS.
No one knows for sure why some people with small-cell lung cancer develop such antibodies and why some dont.
Sometimes LEMS that is associated with cancer is called T-LEMS.
Idiopathic LEMS
Some people get LEMS, even though they dont have an underlying cancer.
Its thought that antibodies to these calcium channels are also present, as they are for people with T-LEMS.
These individuals are said to have idiopathic LEMS.
People with T-LEMS are more likely to be men than women.
Diagnosis happens around an average age of 60.
When brought on by an underlying cancer, LEMS belongs to a larger group of conditions known asparaneoplastic syndromes.
Diagnosis
Unfortunately, a correct diagnosis of LEMS doesnt always happen right away.
Because it is such a rare disease, its important that clinicians think of it as a possibility.
Neurologists can bring special expertise to the diagnostic process.
Because LEMS is sometimes due to cancer, it is important to be correctly diagnosed as quickly as possible.
Medical History and Clinical Exam
Medical history and clinical exam are critical parts of diagnosis.
Through these alone, a clinician might suspect LEMS.
Your clinician should ask about all your current symptoms as well as your other medical conditions.
It’s especially important to ask about autonomic symptoms.
The medical exam itself, especially a completeneurological exam, also gives important clues.
Its also important to investigate medical symptoms or exam findings that might make lung cancer more likely.
For example, your healthcare provider should ask about whether youve ever smoked and whether you have a cough.
Healthcare providers need to distinguish LEMS from other possibilities that might cause some similar symptoms.
For example, a condition calledmyasthenia gravishas some similar symptoms, and it is much more common than LEMS.
However, it is more likely to cause eye symptoms than LEMS.
If a clinician is concerned about LEMS, some other diagnostic tests can be helpful.
Antibody Tests
Antibody tests are very helpful in confirming a diagnosis.
(You might see these written as P/Q pop in VGCCs.)
However, these tests are not perfect.
Also, a small percentage of people with LEMS do not have high amounts of these antibodies.
On the other hand, some types of antibody tests can help to eliminate other possible causes.
Your healthcare provider might also order antibody tests for acetylcholine receptors.
Electrophysiology Tests
Sometimeselectrophysiology testscan help confirm a diagnosis as well.
A test like electromyography (EMG) can provide some helpful information.
In both, an electrode is inserted into your muscle and the electrical activity is monitored.
These two types of tests are usually performed during the same visit.
For example, you may need a biopsy of the cancerous area.
However, we do have some therapies that can help reduce symptoms.
This may be helpful both for people with idiopathic LEMS and people with LEMS from cancer.
The most recommended treatment is Firdapse.
(The generic name is amifampridine or 3,4-DAP).
The version of the medication that has been FDA approved for children is sold under the name Ruzurgi.
This drug allows more of the calcium channels to open when the nerve signals, decreasing symptoms.
Unfortunately, this treatment can cause some side effects, especially as the dose increases.
This may limit the amount you could take.
If this is the case, your clinician may want to try additional medications or therapies.
Other options are therapies that tone down a persons immune response.
For example, you might take a steroid such asprednisolone.
Another immunosuppressive agent, like azathioprine, might be taken in addition to the steroid.
Other possible treatment options are intravenous immunoglobulin and plasma exchange therapy.
However, none of these other choices are as well-established as Firdapse.
With successful cancer treatment, the symptoms of LEMS often go away.
If so, you might benefit from the same medications used for idiopathic LEMS.
Tumor Surveillance
Tumor surveillance is another key part of treatment.
This can ensure that a potential cancer is detected and treated as soon as possible.
Factors that increase risk include history of smoking, age of 50 or older, and recent weight loss.
People at high risk might need to be screened every six months over a period of two years.
People without risk factors might need only one repeat imaging test.
People who have LEMS without an underlying cancer do not seem to have a shortened life span.
However, you might still have some physical limitations, even after youve explored all your treatment options.
Though you might have some residual symptoms, these seem to plateau with treatment and time in most people.
11(8):e5450.
doi:10.7759/cureus.5450
Ivanovski T, Miralles F.Lambert-Eaton myasthenic syndrome: early diagnosis is key.Degener Neurol Neuromuscul Dis.
2:31-37. doi:10.2147/ITT.S31971
Kesner VG, Oh SJ, Dimachkie MM, Barohn RJ.Lambert-Eaton myasthenic syndrome.Neurol Clin.
(2):CD003279.
doi:10.1002/14651858
National Institutes of Health.
National Cancer Institute.Small cell lung cancer treatmenthealth professional version.
2020 Feb 4;94(5):e511-e520.
