199. Lambert-Eaton Myasthenic Syndrome

Question 1

What is Lambert-Eaton myasthenic syndrome (LEMS)?

Answer 1

An autoimmune channelopathy that results in decreased release of acetylcholine (ACh) at the neuromuscular junction due to autoantibodies against calcium channels.

Question 2

What occurs at the neuromuscular junction during normal functioning?

Answer 2

An action potential opens voltage-gated calcium channels, allowing calcium ions to enter, bind to proteins on ACh vesicles, prompting the release of ACh.

Question 3

What is the effect of LEMS on muscle contraction?

Answer 3

Results in muscle weakness due to insufficient ACh release.

Question 4

What is the approximate prevalence of LEMS?

Answer 4

Affects approximately 1 in 100,000 individuals, with a slightly higher prevalence in males.

Question 5

At what age does LEMS typically present?

Answer 5

Typically affects persons over the age of 40, but age of onset can vary.

Question 6

What are the most common neoplasms associated with LEMS?

Answer 6

Small cell lung cancer and gastrointestinal malignancies.

Question 7

What percentage of individuals with LEMS do not have an associated neoplasm?

Answer 7

Approximately 40%.

Question 8

What is a distinguishing feature of muscle weakness in LEMS compared to myasthenia gravis (MG)?

Answer 8

LEMS causes proximal limb muscle weakness, worse in lower extremities, while MG affects extraocular and bulbar muscles.

Question 9

What symptom improvement is observed in LEMS with activity?

Answer 9

Improvement in strength due to buildup of presynaptic calcium.

Question 10

What autonomic dysfunction symptoms can be associated with LEMS?

Answer 10

Dry mouth, gastroparesis, urinary retention, orthostatic hypotension, erectile dysfunction.

Question 11

How is LEMS diagnosed?

Answer 11

Through detailed history, physical examination, and electrophysiology.

Question 12

What is a key diagnostic finding in electromyography (EMG) for LEMS?

Answer 12

An increase in response of more than 60%–100% after exercise.

Question 13

What imaging should be performed after confirming a diagnosis of LEMS?

Answer 13

Imaging of the chest to rule out small cell lung cancer.

Question 14

What is the main treatment approach for LEMS associated with neoplasm?

Answer 14

Treating the cancer can result in resolution of LEMS.

Question 15

What are the two potassium channel blockers approved for LEMS treatment in the U.S.?

Answer 15

• Firdapse (3,4-diaminopyridine or 3,4-DAP)
• Ruzurgi (amifampridine)

Question 16

What is the common cholinesterase inhibitor used for LEMS?

Answer 16

Pyridostigmine.

Question 17

What are some immunosuppressive drugs used in LEMS treatment?

Answer 17

• Prednisone
• Azathioprine
• Mycophenolate mofetil
• Cyclosporine

Question 18

What is the role of intravenous immunoglobulin (IVIG) in LEMS treatment?

Answer 18

Decreases immune system antibody production and blocks antibody binding.

Question 19

What anesthetic considerations are necessary for patients with LEMS?

Answer 19

Careful preoperative evaluation, sensitivity to neuromuscular blocking drugs, and vigilant monitoring.

Question 20

True or False: Patients with LEMS can be treated with standard doses of neuromuscular blocking agents.

Answer 20

False.

Question 21

What should be monitored postoperatively in patients with LEMS?

Answer 21

Monitoring for respiratory failure and other complications.