Lambert-Eaton myasthenic syndrome (Eaton-Lambert syndrome)

• What is Lambert-Eaton Syndrome or Eaton-Lambert Syndrome
• Statistics on Lambert-Eaton Syndrome or Eaton-Lambert Syndrome
• Risk Factors for Lambert-Eaton Syndrome or Eaton-Lambert Syndrome
• Progression of Lambert-Eaton Syndrome or Eaton-Lambert Syndrome
• Symptoms of Lambert-Eaton Syndrome or Eaton-Lambert Syndrome
• Clinical Examination of Lambert-Eaton Syndrome or Eaton-Lambert Syndrome
• How is Lambert-Eaton Syndrome or Eaton-Lambert Syndrome Diagnosed?
• Prognosis of Lambert-Eaton Syndrome or Eaton-Lambert Syndrome
• How is Lambert-Eaton Syndrome or Eaton-Lambert Syndrome Treated?
• Lambert-Eaton Syndrome or Eaton-Lambert Syndrome References

What is Lambert-Eaton Syndrome or Eaton-Lambert Syndrome

Lambert-Eaton syndrome is a disease of the neuromuscular junction. A syndrome is a constitution of symptoms or conditions that occur together with the clinical significance that there may be presence of a certain disease.
Lambert-Eaton syndrome is a disease that is characterised by muscle weakness that improves with continued contraction of the muscle.
Lambert-Eaton syndrome is also known as Eaton-Lambert syndrome or Lambert-Eaton myasthenic syndrome because of the close similarity to another disease called myaesthenia gravis.
Lambert-Eaton syndrome affects the muscle and also the autonomic nervous system. Autonomic nervous system controls the involuntary part of the nerve system, for example, sweating mechanism, salivation, gut movement, and sexual function (erection).

Statistics on Lambert-Eaton Syndrome or Eaton-Lambert Syndrome

Lambert-Eaton syndrome is considered to be an extremely rare condition. The true number of cases of Lambert-Eaton syndrome is unknown. It is associated with 3% of patients with a fatal and rapidly destructive form of lung cancer, called small cell lung cancer, and this equates to 4 in 1 million of the population in the United States.
However, this figure excludes the population that has Lambert-Eaton syndrome without small cell lung carcinoma.

Risk Factors for Lambert-Eaton Syndrome or Eaton-Lambert Syndrome

This is a disease of the middle aged to elderly population, which may be due to the association of small cell lung cancer (a disease of the middle aged to elderly).
However, case reports documented that Lambert-Eaton syndrome had occurred in children younger than 17 years old.
There is no gender predilection in Lambert-Eaton syndrome although small cell lung carcinoma is more common in men.

Progression of Lambert-Eaton Syndrome or Eaton-Lambert Syndrome

Lambert-Eaton syndrome is a disease of the neuromuscular junction, i.e. the junction of the nerve ending and muscle fibre. It can be considered as an autoimmune disease. For normal muscle contraction, the nerve ending will release a biochemical substance called acetylcholine (ACh), which then binds to the motor fibre and stimulate contraction. In Lambert-Eaton syndrome, the nerve fibre is unable to release adequate ACh, resulting in weak muscle contraction.
It is thought that in small cell lung cancer, the body’s immune system is activated and hence leading to the above changes.
The significance of this syndrome is the association with small cell lung cancer, the most fatal and rapidly progressing of lung cancers. Approximately 50-60% of the patients with Lambert-Eaton syndrome have this association. The diagnosis of Lambert-Eaton syndrome may suggest the presence of the tumour long before it would otherwise be detected, allowing early removal.
Other cancers associated with Lambert-Eaton syndrome include lymph node cancers, thymus cancer, bladder cancer, and cancers of the major organs.

How is Lambert-Eaton Syndrome or Eaton-Lambert Syndrome Diagnosed?

Depending on the cause, the patient may need general routine investigations, especially if the cause cannot be explained by clinical history and examination. These include looking at the blood function, kidney function, liver function, thyroid function, and the body’s iron, vitamin and electrolyte levels.

Prognosis of Lambert-Eaton Syndrome or Eaton-Lambert Syndrome

The prognosis of Lambert-Eaton syndrome lies in the underlying cause. Small cell lung carcinoma has a very bad prognosis.
Otherwise, Lambert-Eaton syndrome is generally benign but may cause significant inconvenience in activities of daily living, as progressive muscle weakness can profoundly affects the patients’ ability to perform activities.

How is Lambert-Eaton Syndrome or Eaton-Lambert Syndrome Treated?

The treatment aims at treating the underlying conditions such as small cell lung cancer. This will not be discussed in details here. However, due to poor prognosis and possible widespread of the malignancy, supportive and palliative care will be provided.
Otherwise, for the treatment of Lambert-Eaton syndrome itself, several areas of research are still underway. Suppressing the immune system can help the symptoms in the short term, and these include:
 

• Intravenous gammaglobulin (intragam): This involves flooding of the body’s autoantibodies and binding to them so that they do not bind as much to the presynaptic terminals.
• Plasmapheresis: This involves extracting a portion of the body’s autoantibodies towards the nerve fibres.

 
Longer term treatment involves using 3,4-diaminopyridine (DAP) which increases the release of acetylcholine from the nerves.

Lambert-Eaton Syndrome or Eaton-Lambert Syndrome References

[1] eMedicine: Lambert-Eaton myasthenic syndrome [online]. 2005. [Cited 2005 October 24th]. Available from: URL: http://www.emedicine.com/EMERG/topic292.htm
[2] McEvoy, KM, Windebank, AJ, Daube, JR, Low, PA. 3,4-Diaminopyridine in the treatment of Lambert-Eaton myasthenic syndrome. N Engl J Med 1989; 321:1567
[3] Newsom-Davis, J, Murray, NM. Plasma exchange and immunosuppressive drug treatment in the Lambert- Eaton myasthenic syndrome. Neurology 1984; 34:480
[4] Sanders, DB, Massey, JM, Sanders, LL, Edwards, LJ. A randomized trial of 3,4-diaminopyridine in Lambert-Eaton myasthenic syndrome. Neurology 2000; 54:603
[5] Up to Date: Paraneoplastic syndromes of the nervous system [online]. 2005. [Cited 2005 October 24th]. Available from: URL: http://www.utdol.com/application/topic.asp?file=brain_ca/13490&type=A&selectedTitle=1~7
[6] Wirtz, PW, Nijnuis, MG, Sotodeh, M, et al. The epidemiology of myasthenia gravis, Lambert-Eaton myasthenic syndrome and their associated tumours in the northern part of the province of South Holland. J Neurol 2003; 250:698