Summary about Disease
Lambert-Eaton Myasthenic Syndrome (LEMS) is a rare autoimmune disorder that affects the connection between nerves and muscles. It is characterized by muscle weakness, primarily affecting the limbs, and often associated with small cell lung cancer. In LEMS, the body's immune system mistakenly attacks the voltage-gated calcium channels (VGCCs) on nerve endings at the neuromuscular junction, disrupting the release of acetylcholine, a neurotransmitter crucial for muscle contraction.
Symptoms
Common symptoms of LEMS include:
Muscle weakness, typically starting in the legs and progressing upwards.
Fatigue
Dry mouth
Constipation
Erectile dysfunction in men
Drooping eyelids (ptosis)
Double vision (diplopia)
Difficulty swallowing (dysphagia)
Impaired speech
Decreased or absent reflexes A characteristic feature of LEMS is that muscle strength may temporarily improve with repeated exertion or exercise.
Causes
LEMS is an autoimmune disorder. In most cases, it's triggered when the body's immune system mistakenly attacks voltage-gated calcium channels (VGCCs) at the nerve endings that control muscle movement. These channels are essential for releasing acetylcholine, a neurotransmitter that signals muscles to contract.
Associated with Cancer: About 50-60% of LEMS cases are associated with an underlying cancer, most commonly small cell lung cancer (SCLC). The immune system targets the cancer cells, which also express similar VGCCs, leading to the autoimmune attack on nerve endings.
Without Cancer (Idiopathic LEMS): In cases where LEMS is not associated with cancer, the trigger for the autoimmune response is unknown.
Medicine Used
Treatment for LEMS focuses on improving neuromuscular transmission and managing the underlying cause, especially if cancer is present. Medications include:
3,4-Diaminopyridine (3,4-DAP): This medication enhances the release of acetylcholine from nerve endings. It's often the first-line treatment.
Immunosuppressants: Medications like prednisone, azathioprine, mycophenolate mofetil, and rituximab can suppress the immune system's attack on the nerve endings.
Intravenous Immunoglobulin (IVIg): Provides temporary relief by supplying healthy antibodies to modulate the immune system.
Plasma Exchange (Plasmapheresis): Removes harmful antibodies from the blood.
Amifampridine phosphate (Firdapse): Another form of 3,4-DAP. If LEMS is associated with small cell lung cancer, treatment of the cancer is crucial and can often improve LEMS symptoms.
Is Communicable
LEMS is not a communicable disease. It is an autoimmune disorder, meaning it cannot be spread from person to person through any form of contact.
Precautions
While there are no specific precautions to prevent LEMS, individuals with LEMS should:
Manage Underlying Conditions: If LEMS is associated with cancer, focus on cancer treatment.
Avoid Certain Medications: Certain drugs can worsen muscle weakness. Discuss all medications with your doctor. These include: Certain antibiotics (aminoglycosides, fluoroquinolones), Beta-blockers, Calcium channel blockers, Muscle relaxants, Quinine.
Avoid Excessive Heat: Hot environments can exacerbate muscle weakness.
Maintain a Healthy Lifestyle: Balanced diet, moderate exercise as tolerated, and adequate rest.
How long does an outbreak last?
LEMS is a chronic condition, not an outbreak. Symptoms are typically ongoing and require continuous management. There may be fluctuations in symptom severity, but it doesn't resolve on its own like an infectious disease. The course of the disease depends on whether it is associated with cancer and how effectively the underlying cause (cancer or the autoimmune response) is managed.
How is it diagnosed?
Diagnosis of LEMS involves:
Clinical Evaluation: Assessment of symptoms, medical history, and physical examination.
Neurological Examination: Testing muscle strength, reflexes, and nerve function.
Electrophysiological Studies:
Repetitive Nerve Stimulation (RNS): Shows a characteristic increase in muscle response with repeated stimulation at faster rates.
Single-Fiber Electromyography (SFEMG): Can detect subtle abnormalities in neuromuscular transmission.
Blood Tests:
Voltage-Gated Calcium Channel (VGCC) Antibody Test: Detects antibodies against VGCCs, which are highly specific for LEMS.
Chest Imaging: If LEMS is suspected, especially in smokers or those with a history of smoking, chest X-ray or CT scan to look for lung cancer.
Timeline of Symptoms
The onset of LEMS symptoms can be gradual. A typical timeline includes:
Early Symptoms: Often, the first symptom is weakness in the legs, leading to difficulty walking or climbing stairs. Other early symptoms might include fatigue, dry mouth, or constipation.
Progression: Over weeks to months, weakness may progress to involve the arms and other muscle groups. Other symptoms like drooping eyelids, double vision, or difficulty swallowing may appear.
Diagnosis: Diagnosis can be delayed due to the rarity of the disease and the similarity of symptoms to other neuromuscular disorders.
Treatment: After diagnosis, treatment is initiated, which may improve symptoms.
Long-Term: LEMS is a chronic condition requiring ongoing management. The long-term prognosis depends on the underlying cause (especially the presence or absence of cancer) and the effectiveness of treatment.
Important Considerations
Cancer Screening: If diagnosed with LEMS, especially if a smoker or former smoker, a thorough cancer screening is crucial to rule out small cell lung cancer.
Drug Interactions: Be aware of medications that can worsen muscle weakness. Discuss all medications, including over-the-counter drugs and supplements, with your doctor.
Pregnancy: LEMS can affect pregnancy. Discuss family planning with your doctor.
Support Groups: Joining support groups can provide valuable emotional support and information.
Neurologist Specialization: Seek care from a neurologist with experience in neuromuscular disorders.