Lambert-Eaton Myasthenic Syndrome (LEMS)

LEMS is a rare autoimmune disease that affects about 1 in every 300,000 people worldwide. In LEMS, the body attacks nerve cells that control a chemical called acetylcholine (ACh). ACh is an important chemical because it helps send messages between the nerve cells and the muscle cells. In LEMS, the nerve cells lose the ability to release ACh and that effects how muscles work. LEMS causes muscles to feel weak because it affects the neuromuscular junction—the place where nerve cells meet muscle cells.1-3

LEMS can occur at any age, but is commonly diagnosed in people who are over 40 years of age. Approximately 50% of people with LEMS also develop cancer—the most common form is a type of lung cancer called small cell lung cancer (SCLC), this is also known as paraneoplastic LEMS. Paraneoplastic LEMS typically occurs in people with a history of smoking and who are 50 years of age or older. Cancer is an important diagnostic criteria in people with LEMS, so cancer testing is recommended.

Symptoms of LEMS1,2

In LEMS, general muscle weakness, especially in the legs, is typically the first sign of the disease. People with LEMS may find it difficult to walk, get up from a chair, climb steps, or get out of a car. Other symptoms include:

  • Tingling sensations
  • Fatigue
  • Falling down
  • Slurred speech
  • Trouble with your vision
  • Difficulty swallowing
  • Always feeling tired
  • Dry mouth, eyes, skin
  • Impotence
  • Constipation
  • Less often: weakness in the muscles of your eyes and neck


Because LEMS is so rare and its symptoms are similar to many other diseases, it is frequently misdiagnosed. LEMS is commonly mistaken for fibromyalgia, lupus, myasthenia gravis (MG) and multiple sclerosis. MG and other conditions, like Guillain-Barre syndrome, amyotrophic lateral sclerosis (ALS), or other neuromuscular diseases, may need to be ruled out before the correct diagnosis of LEMS is reached.

A diagnosis of LEMS is generally made on the basis of clinical symptoms during a physical examination, the degree of muscle weakness, your reflexes, and the function of your nervous system. Typically, people get electrodiagnostic tests, in which the nerves are stimulated electrically and the nerve impulses in the muscles are measured. Blood tests to check on the function of your immune system are also common.


Currently, there is no FDA-approved treatment for LEMS, but there are drug therapies and procedures that can help reduce the symptoms of LEMS. The aim of current treatments is to decrease the autoimmune response, helping to prevent your body from attacking its own cells.

Treatments include:

  • Steroids, which help suppress your immune system
  • Intravenous immunoglobulin, which helps “mop up” immune cells
  • Plasmapheresis, which filters your blood through a machine that removes overactive immune cells and then infuses the cleansed blood back into your bloodstream
  • Drugs that help improve the electrical impulses between your nerve cells and muscle cells


When considering treatment options, which are limited, patients with LEMS should consult with a board-certified neurologist who specializes in neuromuscular diseases. Catalyst Pharmaceuticals is working towards securing FDA approval for amifampridine phosphate for the treatment of LEMS.

Catalyst is currently making amifampridine phosphate available on a compassionate-use basis while it seeks FDA approval. (Learn More About the Amifampridine Phosphate Expanded Access Program)

What Is LEMS?

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  1. Titulaer MJ, Lang B and Verschuuren JJ. Lambert-Eaton myasthenic syndrome: from clinical characteristics to therapeuticstrategies. Lancet Neurol. 2011;10(12):1098-1107
  2. Harms L, Sieb JP, Williams AE, et al. Long-term disease history, clinical symptoms, health status, and healthcare utilization in patients suffering from Lambert Eaton myasthenic syndrome: results of a patient interview survey in Germany. J Med Econ. 2012;15(3):521-530.
  3. Orpha.net. Lambert-Eaton myasthenic syndrome [sc name=”Exit Link” exitLink=”http://www.orpha.net/consor/cgi-bin/Disease_Search.php?lng=EN&data_id=10583&Disease_Disease_Search_diseaseGroup=Lambert-Eaton-myasthenic-syndrome&Disease_Disease_Search_diseaseType=Pat&Disease(s)/group%20of%20diseases=Lambert-Eaton-myasthenic-syndrome&title=Lambert-Eaton-myasthenic-syndrome&search=Disease_Search_Simple” linkText = “http://www.orpha.net/consor/cgi-bin/Disease_Search.php?lng=EN&data_id=10583&Disease_Disease_Search_diseaseGroup=Lambert-Eaton-myasthenic-syndrome&Disease_Disease_Search_diseaseType=Pat&Disease(s)/group%20of%20diseases=Lambert-Eaton-myasthenic-syndrome&title=Lambert-Eaton-myasthenic-syndrome&search=Disease_Search_Simple”] Accessed December 13, 2017

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