Lambert Eaton Myasthenic Syndrome

Question 1

What is lambert eaton syndrome?

Answer 1

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease — a disease in which the immune system attacks the body’s own tissues. The attack occurs at the connection between nerve and muscle (the neuromuscular junction) and interferes with the ability of nerve cells to send signals to muscle cells.

Specifically, the immune system attacks the calcium channels on nerve endings that are required to trigger the release of chemicals (acetylcholine). With fewer calcium channels, the nerve ending releases less acetylcholine. Acetylcholine is a chemical messenger that triggers muscle contraction. In people with LEMS, the lowered levels of acetylcholine are not sufficient to cause normal muscle contractions, causing muscle weakness.

Question 2

What are the symptoms of LEMS?

Answer 2

• weakness in the upper legs and hips
• leads to difficulty walking
• can result in weakness of the eye muscles and those in talking, swallowing, chewing (normally mild- more likely in MG)

Question 3

What are the features of lambert eaton syndrome?

Answer 3

repeated muscle contractions lead to increased muscle strength (in contrast to myasthenia gravis)
in reality, this is seen in only 50% of patients and following prolonged muscle use muscle strength will eventually decrease
limb-girdle weakness (affects lower limbs first)
hyporeflexia
autonomic symptoms: dry mouth, impotence, difficulty micturating
ophthalmoplegia and ptosis not commonly a feature (unlike in myasthenia gravis)

Question 4

What would you see on EMG in lambert eaton syndrome?

Answer 4

incremental response to repetitive electrical stimulation

Question 5

What is lambert eaton syndrome seen in?

Answer 5

Seen in association with small cell lung cancer and to a lesser extent breast and ovarian cancer
Can also occur independently as an auto immune disorder

Question 6

What is the management of lambert eaton syndrome?

Answer 6

treatment of underlying cancer
immunosuppression, for example with prednisolone and/or azathioprine
3,4-diaminopyridine is currently being trialled
works by blocking potassium channel efflux in the nerve terminal so that the action potential duration is increased. Calcium channels can then be open for a longer time and allow greater acetylcholine release to the stimulate muscle at the end plate
intravenous immunoglobulin therapy and plasma exchange may be beneficial