Lambert Eaton syndrome

Lambert-Eaton Myasthenic Syndrome Lambert-Eaton Myasthenic Syndrome (LEMS) is a rare autoimmune disorder characterized by muscle weakness of the limbs. It is often associated with certain types of cancer, most notably small cell lung cancer. This condition is named after Edward Lambert and Lee Eaton, who first described it in the 1950s.

Pathophysiology

LEMS is caused by an autoimmune attack on the voltage-gated calcium channels (VGCC) located on the presynaptic membrane of the neuromuscular junction. This attack reduces the release of acetylcholine, a neurotransmitter essential for muscle contraction, leading to muscle weakness.

Autoimmune Mechanism

The immune system mistakenly targets the VGCCs, which are crucial for the release of acetylcholine. This results in impaired neuromuscular transmission. The exact trigger for this autoimmune response is not fully understood, but it is often associated with the presence of a tumor, particularly small cell lung cancer, which may express similar antigens.

Clinical Features

Patients with LEMS typically present with proximal muscle weakness, which affects the muscles closest to the trunk, such as the hips and shoulders. Other symptoms may include:

• Fatigue
• Difficulty climbing stairs or rising from a seated position
• Dry mouth
• Erectile dysfunction
• Reduced or absent reflexes

Diagnosis

Diagnosis of LEMS involves a combination of clinical evaluation, electromyography (EMG), and blood tests to detect antibodies against VGCCs. A chest CT scan may be performed to check for the presence of an underlying tumor.

Electromyography (EMG)

EMG studies in LEMS show a characteristic pattern of low-amplitude muscle responses that increase after exercise or repeated stimulation, known as facilitation.

Treatment

Treatment of LEMS focuses on managing symptoms and addressing any underlying cancer. Options include:

• 3,4-Diaminopyridine (3,4-DAP): A potassium channel blocker that enhances acetylcholine release.
• Immunosuppressive therapy: Such as corticosteroids or azathioprine to reduce the autoimmune response.
• Plasmapheresis or intravenous immunoglobulin (IVIG): To remove antibodies from the blood.

Prognosis

The prognosis of LEMS varies depending on the presence and treatment of an associated tumor. Patients without cancer generally have a better prognosis, while those with small cell lung cancer may have a more guarded outlook.

See Also

• Myasthenia Gravis
• Autoimmune Disorders
• Neuromuscular Junction
• Lambert, E. H., & Eaton, L. M. (1957). "The syndrome of myasthenic weakness with small cell carcinoma of the lung."
• Lennon, V. A., & Lambert, E. H. (1989). "Autoantibodies to calcium channels in the Lambert-Eaton myasthenic syndrome."

NIH genetic and rare disease info

• NIH info on Lambert Eaton syndrome

Lambert Eaton syndrome is a rare disease.