Lambert-Eaton Myasthenic Syndrome (LEMS)
A rare autoimmune disorder of nerve-to-muscle signaling
Quick Facts
- Type: Autoimmune neuromuscular disorder
- Hallmark: Leg weakness, often eases briefly with use
- Linked to: Small cell lung cancer in many cases
- Other signs: Dry mouth, reduced reflexes
Overview
Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder that affects the junction where nerves communicate with muscles. The immune system produces antibodies against calcium channels on nerve endings, which reduces the release of a chemical messenger needed to activate muscles. The result is muscle weakness, most noticeably in the thighs and hips.
In a substantial proportion of cases, LEMS occurs alongside cancer, most often small cell lung cancer, and the muscle symptoms can appear before the cancer is detected. In other people, no cancer is found and the disorder is purely autoimmune. Because the weakness can be subtle and resembles other conditions, diagnosis can be delayed, but recognizing its distinctive features is important for both treating the weakness and prompting a search for an underlying cancer.
Symptoms
The most prominent symptom is muscle weakness, with some features that help distinguish LEMS from similar conditions:
- Weakness in the muscles of the hips and thighs, causing difficulty climbing stairs or rising from a chair
- A waddling gait and trouble walking
- Weakness that may briefly improve after a short period of activity, then worsen again
- Reduced or absent reflexes (such as the knee-jerk)
- Dry mouth, constipation, and other signs of autonomic nervous system involvement
- Sometimes mild drooping eyelids or double vision, though these are usually less prominent than in myasthenia gravis
If weakness affects the muscles used for breathing or swallowing, this is serious and needs urgent medical attention.
Causes
LEMS is an autoimmune disorder, meaning the immune system mistakenly attacks the body's own tissue. Specifically:
- Antibodies against calcium channels: These antibodies target voltage-gated calcium channels on nerve endings, reducing release of acetylcholine and weakening muscle activation.
- Cancer-associated form: In many people, the trigger is a cancer, most often small cell lung cancer, in which the tumor sets off the immune response.
- Non-cancer (autoimmune) form: In others, no tumor is found and the autoimmune process occurs on its own, sometimes with other autoimmune conditions.
Risk Factors
- Smoking and other factors that increase the risk of small cell lung cancer
- Older age, particularly for the cancer-associated form
- A history of other autoimmune conditions
- The disorder can occur in people without any of these factors
Diagnosis
Diagnosing LEMS involves confirming the neuromuscular problem and searching for any underlying cancer:
- Neurological exam: Testing strength, reflexes, and how weakness changes with activity.
- Nerve conduction studies and electromyography (EMG): Specialized tests can show the characteristic increase in muscle response after brief exercise.
- Blood tests: Detecting antibodies against calcium channels supports the diagnosis.
- Cancer screening: Chest imaging, often a CT scan, is done to look for lung cancer, sometimes repeated over time.
Because LEMS can be the first sign of an undiagnosed cancer, evaluation for malignancy is a key part of the workup.
Treatment
Treatment targets both the weakness and any underlying cancer:
- Treating the cancer: When LEMS is linked to cancer, treating the tumor often improves the muscle symptoms.
- Medications to improve nerve signaling: Drugs such as amifampridine help nerves release more of the messenger that activates muscles.
- Immune-directed therapies: Corticosteroids, other immunosuppressants, intravenous immunoglobulin (IVIG), or plasma exchange may be used to reduce the harmful antibodies.
Care is usually coordinated by a neurologist, and when cancer is involved, by an oncology team as well. Treatment is tailored to each person and the underlying cause.
Prevention
LEMS itself cannot be reliably prevented, but some steps reduce related risk and support management:
- Do not smoke, which lowers the risk of small cell lung cancer linked to LEMS
- Attend recommended follow-up and cancer screening if you have been diagnosed
- Report new or worsening weakness promptly so treatment can be adjusted
- Keep your care team informed about all medications, as some can worsen neuromuscular weakness
When to See a Doctor
See a doctor for unexplained, persistent muscle weakness, especially in the hips and thighs, or weakness with dry mouth and reduced reflexes. Seek emergency care immediately if you develop:
- Difficulty breathing or shortness of breath
- Trouble swallowing or choking on food or liquids
- Rapidly worsening weakness
Because LEMS can be associated with lung cancer, any new diagnosis should prompt appropriate cancer evaluation, and persistent unexplained weakness should always be assessed by a doctor.
Frequently Asked Questions
What is Lambert-Eaton syndrome?
It is a rare autoimmune disorder in which antibodies disrupt the signal between nerves and muscles, causing weakness most noticeable in the hips and thighs. It is often associated with small cell lung cancer, and the muscle symptoms can appear before the cancer is found.
How is Lambert-Eaton syndrome different from myasthenia gravis?
Both affect the nerve-muscle junction, but in LEMS weakness mainly affects the legs and may briefly improve with activity, and reflexes are reduced. Myasthenia gravis more often affects the eyes and face and worsens with use. They involve different antibodies and are confirmed by specific tests.
Is Lambert-Eaton syndrome linked to cancer?
Yes, in many people it is associated with cancer, most commonly small cell lung cancer, and the weakness may be the first clue. In others no cancer is found. Because of this link, anyone diagnosed with LEMS undergoes cancer screening, often including chest imaging.
How is Lambert-Eaton syndrome treated?
Treatment includes addressing any underlying cancer, medications such as amifampridine that improve nerve-to-muscle signaling, and immune therapies like steroids, IVIG, or plasma exchange to reduce harmful antibodies. Care is coordinated by a neurologist and, when cancer is present, an oncology team.
When is Lambert-Eaton syndrome an emergency?
Seek emergency care if weakness affects breathing or swallowing, causing shortness of breath, choking, or rapidly worsening weakness. These signs mean vital muscles may be involved and require urgent treatment. Any unexplained, progressive muscle weakness should be evaluated by a doctor.
References
- National Institute of Neurological Disorders and Stroke (NINDS). Lambert-Eaton myasthenic syndrome.
- Genetic and Rare Diseases Information Center (GARD).
- Mayo Clinic. Lambert-Eaton myasthenic syndrome.
- MedlinePlus, U.S. National Library of Medicine.