Lambert-Eaton myasthenic syndrome

The Lambert-Eaton syndrome (LEMS) is a disorder with symptoms very similar to those of myasthenia gravis, in which there is muscle weakness related to the blockage of communication between nerves and muscles.

About 60% of people with LEMS have an underlying malignancy most commonly small cell lung cancer; therefore, it is considered a paraneoplastic syndrome (a condition that arises as a result of cancer in other parts of the body). It is the result of antibodies against presynaptic voltage-gated calcium channels, and probably other nerve terminal proteins, at the neuromuscular junction (the connection between nerves and the muscle they supply). Diagnosis is usually confirmed with electromyography and blood tests..; these also distinguish it from myasthenia gravis, a related autoimmune neuromuscular disease.

Etiology and epidemiology

It is due to an autoimmune response against presynaptic calcium channels. It is rare. More frequent in men than in women (ratio 5:2). In 70% of men (40% of women) it is associated with neoplasia, such as paraneoplastic syndrome, especially small cell carcinoma. Less frequently, it can be seen in breast cancer, prostate cancer, stomach cancer, rectal cancer, lymphomas. In almost a third of the cases no associated tumor is found, especially in children.

Clinical manifestations

Syndrome characterized by marked paresis (weakness) of the proximal muscles (scapular and pelvic girdles), trunk, and lower extremities; morning, which improves as the day progresses.

It may present hyporeflexia (dulled deep tendon reflexes) that characteristically improves with use, which is useful for the differential diagnosis with myasthenia gravis, since in this case the opposite occurs. Areflexia (complete abolition of reflexes) is rare, a finding that forces us to consider the possibility of a polyneuropathy or other lesions in the nerve itself and not in the neuromuscular junction.

The syndrome can be accompanied by paresthesias, periarticular pain, and autonomic dysfunction (dry mouth, constipation, voiding difficulties, impotence). These symptoms are rare in myasthenia gravis.

Diagnosis

Shows marked sensitivity to curare and an inconspicuous response to neostigmine.

Electromyography is helpful in confirming the diagnosis:

• Repetitive stimulation: at high stimulation frequencies (50 stimulations per second), pathological increase responses can be revealed (105 % increase in amplitude). A voluntary contraction of the muscle for 10-15 seconds causes a striking post-ethnic empowerment.
• Simple fiber electromyography: Displays an increase in jitter

Treatment

The syndrome is relieved with polychemotherapy. If treatment is unsuccessful, it may be beneficial to administer diaminopyridine, 10-25 mg orally, 4 times a day. The symptoms worsen with the use of calcium antagonists, so these drugs are contraindicated in this syndrome.