Lambert–Eaton myasthenic syndrome

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Lambert–Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder that affects the neuromuscular junction, the site where nerve cells communicate with muscles. It is characterized by muscle weakness and fatigue, particularly in the proximal muscles, which are the muscles closest to the trunk of the body.

Pathophysiology

LEMS is caused by autoantibodies that target voltage-gated calcium channels (VGCCs) on the presynaptic nerve terminals. These autoantibodies inhibit the release of acetylcholine, a neurotransmitter essential for muscle contraction. The reduction in acetylcholine release leads to the characteristic muscle weakness seen in LEMS.

Symptoms

The primary symptoms of LEMS include:

• Muscle weakness, especially in the upper legs and hips
• Fatigue
• Difficulty climbing stairs or rising from a seated position
• Dry mouth
• Erectile dysfunction in men
• Autonomic dysfunction, such as constipation and blurred vision

Diagnosis

The diagnosis of LEMS is typically based on clinical evaluation, electromyography (EMG), and the detection of anti-VGCC antibodies in the blood. EMG studies often show a characteristic incremental response to repetitive nerve stimulation.

Treatment

Treatment for LEMS may include:

• Medications to enhance acetylcholine release, such as 3,4-diaminopyridine (3,4-DAP)
• Immunosuppressive therapies, such as corticosteroids and azathioprine
• Plasmapheresis or intravenous immunoglobulin (IVIG) to reduce the levels of autoantibodies

Prognosis

The prognosis for individuals with LEMS varies. Some patients respond well to treatment and experience significant improvement in muscle strength and function. However, LEMS is often associated with underlying malignancies, particularly small cell lung cancer, which can affect the overall prognosis.

Related Conditions

LEMS is often associated with other autoimmune disorders and malignancies. It is important to screen for underlying cancers, especially in older patients and smokers.

See Also

• Myasthenia gravis
• Autoimmune disease
• Neuromuscular junction
• Small cell lung cancer
• Electromyography