Lambert-Eaton Myasthenic Syndrome
What is Lambert-Eaton Myasthenic Syndrome?
Also known as Lambert-Eaton myasthenic syndrome, LEMS and Eaton-Lambert syndrome, Lambert-Eaton syndrome is a rare neurological syndrome that occurs when the transmission of electrical signals from the nerves to the muscles is disturbed.
Who is affected?
Lambert-Eaton myasthenic syndrome affects around 1 in every 250,000-330,000 people. 1 in 2 people are affected as a result of underlying conditions, most notably lung cancer. Other cases appear to have no clear cause.
What causes Lambert-Eaton syndrome?
Lambert-Eaton occurs when nerve signals are not sent to the muscles in the usual way. It is caused by an immune response, which triggers a release of antibodies that attack the nerve endings, resulting in disrupted signals. Attacking the nerve endings reduces the amount of acetylcholine by the nerve endings and this means that the signals are not strong enough to make the muscles move normally. The muscles become weak and this affects your mobility and strength.
Sometimes, the nerve endings in the autonomic nervous system can also be affected. When this is the case, symptoms such as blurred vision and dry mouth may become apparent.
Symptoms of Lambert-Eaton syndrome
It is common for Lambert-Eaton syndrome to affect muscle strength and subsequently, movement. The muscles tend to feel weak and achy and even the most routine actions, such as walking up the stairs or standing up, may become more of a challenge. Walking can become increasingly difficult and the legs may feel heavy and unresponsive. If the neck muscles are affected, this can make swallowing difficult and affect speech. It may also become increasingly hard to hold the head properly. Less commonly, the eyes are affected and this can result in droopy eyelids.
Sometimes, the autonomic nervous system is affected and this has implications for actions that we do hundreds of times a day without even thinking about it. This system is responsible for controlling breathing and swallowing among many other things. Symptoms that may occur when the autonomic nervous system is affected include erectile dysfunction, blurred vision, dizziness or feeling faint (especially after standing from a sitting position) and constipation.
Lambert-Eaton syndrome and lung cancer
Around half of those affected by Lambert-Eaton syndrome suffer from an aggressive form of lung cancer known as small cell lung cancer. In very rare cases, other forms of cancer may also cause Lambert-Eaton syndrome.
Diagnosing Lambert-Eaton syndrome
A GP will look at symptoms and carry out some basic tests to see if further investigation is required. If a doctor suspects that a patient may have Lambert-Eaton syndrome, they will be referred for specialist tests. There are disorders similar to Lambert-Eaton syndrome and specific neurological tests will usually be ordered to determine a diagnosis and rule out other potential causes. Tests that may be carried out include:
- Blood tests: blood tests can help to identify any antibodies responsible for damaging the nerve endings.
- Nerve conduction: this is a test used to identify potential issues between the nerves and the muscles. In order to see how the nerves interact with the muscles, an electrode is placed under the skin and into the muscle. It then monitors electrical stimulation in the muscle. If there is a lack of response from the muscles, this suggests that the individual may have LEMS.
- Nerve stimulation: nerve stimulation tests look at the transmission of signals from the nerves to the muscles.
Treating Lambert-Eaton syndrome
If Lambert-Eaton syndrome is diagnosed, investigations will be carried out to check for evidence of lung cancer. If lung cancer is detected, this will be treated as a priority and methods include surgery, chemotherapy and radiotherapy. Your care team will explain the treatment options in great detail before any decisions are made.
There is no cure for Lambert-Eaton syndrome, but treatments can help to ease symptoms. Treatment options include:
- increasing acetylcholine production: this is done by using medication known as 3,4-diaminopyridine (DAP)
- increasing the functionality of acetylcholine and prolonging its function: this is done using a type of medicine called pyridostigmine, which helps to slow the processing of acetylcholine, which makes it last for longer
- decreasing the number of antibodies: this is done by using immunosuppressants or steroids
In milder cases, DAP and pyridostigmine tend to be used. They are often used in combination. If they are ineffective, steroids or immunosuppressants may be recommended. Most medications carry a risk of side-effects. Possible side effects include:
Pyridostigmine: stomach pain, diarrhoea, feeling sick and muscle spasms. Steroids: gaining weight and an increased risk of diabetes, osteoporosis, high blood pressure and cataracts. These effects are associated with high dosages.
In more severe cases, immunoglobulin therapy or plasmapheresis may be recommended. Plasmapheresis involves using a machine to remove the plasma from the blood, while immunoglobulin therapy involves being given an injection of donor blood antibodies. It helps to alter the way your immune system functions. Usually, both treatments have a very positive effect, but the benefits only last a short period of time.
What is the prognosis?
The prognosis often depends on whether LEMS is caused by lung cancer or not. In cases where small cell lung cancer is present, life expectancy is shortened.
In cases where lung cancer is not present, LEMS does not usually shorten life expectancy. However, it may affect quality of life. Some people respond very well to treatment, while others do not react as well.