What are the other Names for this Condition? (Also known as/Synonyms)

• Lambert-Eaton Syndrome (LES)
• LEMS (Lambert-Eaton Myasthenic Syndrome)
• LES (Lambert-Eaton Syndrome)

What is Lambert-Eaton Myasthenic Syndrome? (Definition/Background Information)

• Lambert-Eaton Myasthenic Syndrome (LEMS) is reportedly an autoimmune disorder that is characterized by progressive muscle weakness at rest, which typically originates from one’s thighs and upper arms
• The muscle weakness experienced may gradually spread to the peripheral and facial region, causing one to have drooping eyes and swallowing difficulties. A diagnosis of Lambert-Eaton Myasthenic Syndrome can be based on clinical signs and symptoms, past medical history, blood serum test, and electrodiagnostic studies
• The muscle weakness observed in Lambert-Eaton Myasthenic Syndrome is postulated to be caused by the immune system attacking one’s own nervous system (autoimmune response). Individuals with small-cell lung cancer or a family history of autoimmune disorders have greater risk for developing LEMS
• Treatment plans are often designed to combat the underlying disease, but medications, such as 3,4-DAP and immunosuppressants, are also available for treating the symptoms of Lambert-Eaton Myasthenic Syndrome
• As Lambert-Eaton Myasthenic Syndrome is a condition caused by an underlying diseases/disorder, the prognosis varies from one individual to another and is mainly dependent on the severity of the underlying causative condition

Who gets Lambert-Eaton Myasthenic Syndrome? (Age and Sex Distribution)

• More than 50% of the Lambert-Eaton Myasthenic Syndrome cases are associated with small-cell lung cancer (SCLC). Individuals that are diagnosed with both LEMS and SCLC are generally older males, aging around 60 years old
• The remaining cases of LEMS that are not associated with SCLC show equal gender distribution with a median age of onset between 50-60 years
• Although, it is rare to see cases of LEMS in children and adolescents, such cases have been reported
• Worldwide, individuals of all races and ethnic groups may be affected

What are the Risk Factors for Lambert-Eaton Myasthenic Syndrome? (Predisposing Factors)

The risk factors for Lambert-Eaton Myasthenic Syndrome (LEMS) include: 

• History of carcinoma, especially small-cell lung cancer
• History of smoking
• Family history of autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, and type I diabetes

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Lambert-Eaton Myasthenic Syndrome? (Etiology)

Lambert-Eaton Myasthenic Syndrome (LEMS) is believed to be caused by an autoimmune attack of nerves controlling muscle movements.

• The immune system generates antibodies that attack cells, infectious organisms, and foreign material in order to protect the body. Occasionally, when such antibodies attack normal cells within the body, it is called an autoimmune response. In other words, an autoimmune attack occurs when the immune system generates antibodies that targets one’s own normal cells
• In the case of LEMS, the individual’s immune system attacks nerves that control muscle movements and reflexes such as the knee jerk reflex. These specific group of nerves that are under attack are nerves that are responsible for making and releasing a chemical that transmits neuronal signal called acetylcholine
• In a majority of cases, individuals with LEMS may also have various cancers, the most common one being small-cell lung cancer (SCLC). In SCLC-LEMS, the immune system generates large amounts of patrolling immune molecules that target tumor cells. However, these molecules also end up attacking the acetylcholine-releasing neurons that controls muscle contraction
• Consequently, acetylcholine quantity decreases significantly. Without sufficient signaling molecules (acetylcholine), the nerves cannot adequately control muscle contractions. The breakdown of communication between one’s nervous system and muscular system ultimately manifest as muscle weakness and loss of tendon reflex

What are the Signs and Symptoms of Lambert-Eaton Myasthenic Syndrome?

The signs and symptoms of Lambert-Eaton Myasthenic Syndrome may include: 

• Progressive muscle weakness starting with the thighs and arms
• Impaired mobility in both lower and upper body
• Muscle pain
• Difficulty with breathing and swallowing 
• Droopy eyelids
• Dryness of mouth
• Diminished tendon reflex such as knee jerk reflex
• Erectile dysfunction
• Constipation

Additionally, the signs and symptoms of the underlying condition, if any present, may be noted.

How is Lambert-Eaton Myasthenic Syndrome Diagnosed?

A diagnosis of Lambert-Eaton Myasthenic Syndrome (LEMS) may involve the following tests and procedures:

• A thorough physical examination and evaluation of individual’s medical history is essential for diagnosis
• Assessment of the presenting signs and symptoms
• Tendon reflex test, such as knee jerk reflex test, may be performed to support the diagnosis, as individuals with LEMS have a diminished tendon reflex
• Blood tests to detect the presence of autoantibodies that targets P/Q-type voltage-gated calcium channels in individual’s blood. These autoantibodies are responsible for the autoimmune attack of acetylcholine-releasing neurons which cause the muscle weakness
• Electrodiagnostic test that involves repetitive nerve stimulation (RNS) may also be performed to diagnose LEMS
• As many individuals with LEMS are also later on diagnosed with small cell lung cancer; therefore, lung checkups through modalities, such as X-ray or CT scan of chest, should also be performed to assist in early diagnosis of potential lung cancer
• Tensilon test, also known as an edrophonium test, is a test that may be used to differentiate myasthenia gravis from LEMS, in order to avoid a misdiagnosis

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Lambert-Eaton Myasthenic Syndrome?

The complications of Lambert-Eaton Myasthenic Syndrome may include the following:

• Severe and debilitating muscle weaknesses causing immobilization
• Complications may arise from the underlying malignancy, such as small-cell lung cancer, or from other associated conditions
• Treatment complications, such as arising from medications used in the treatment of LEMS symptoms. For example, treatment with 3,4-diaminopyridine (3,4-DAP) may result in side effects such as tingling sensation in the fingers and mouth

How is Lambert-Eaton Myasthenic Syndrome Treated?

Medications are often used to treat the symptoms of Lambert-Eaton Myasthenic Syndrome (LEMS). These include:

• 3,4-diaminopyridine, commonly known as 3,4-DAP, is often used to treat the syndrome. It works by stimulating acetylcholine-releasing neurons to release more acetylcholine in an attempt to elevate the concentration of this signaling molecule back to normal levels
• Immunosuppressive medication, such as the combination of prednisone/prednisolone and azathioprine, as well as Rituximab can be given to individuals to reduce autoimmune attacks in the body
• However, it should be noted that the above-mentioned medications only treat the symptoms of LEMS. But, more extensive therapies are necessary to treat the underlying conditions, such small-cell lung cancer, or other cancers and autoimmune disorders

How can Lambert-Eaton Myasthenic Syndrome be Prevented?

• Currently, there are no known methods to prevent Lambert-Eaton Myasthenic Syndrome
• Avoiding cigarette smoking and inhalation of second-hand smoke may reduce the risk of lung cancer
• An early detection and prompt treatment of autoimmune disorders (if any present) is mandated

What is the Prognosis of Lambert-Eaton Myasthenic Syndrome? (Outcomes/Resolutions)

The prognosis of Lambert-Eaton Myasthenic Syndrome (LEMS) depends on the severity of the underlying disease and associated conditions.

• Generally, the prognosis is much more favorable in the absence of associated small-cell lung cancer, with up to 80% of the individuals obtaining substantial improvements in their muscle strength following the administration of immunosuppressive medication
• The presence of LEMS often leads to an increase in the morbidity of the underlying diseases, by causing mobility difficulties and progressive weakness that rapidly worsens (sometimes within months)
• If there is an underlying associated condition, such as small-cell lung cancer, then the prognosis is usually poor; the survival may decrease to just a few months, due to the aggressive nature of this cancer type

Additional and Relevant Useful Information for Lambert-Eaton Myasthenic Syndrome:

The diagnosis of Lambert-Eaton Myasthenic Syndrome often precedes the diagnosis of small-cell lung cancer, or some other forms of cancer. Hence, a diagnosis of LEMS allows for an earlier detection of cancer that can help improve outcomes.