Lambert-Eaton Myasthenic Syndrome (LEMS) is a rare, autoimmune, neuromuscular disorder in which the body attacks and interferes with the communication between nerve and muscle cells. Named for neurologists, Edward Lambert and Lee Eaton who first described LEMS in the 1950s, LEMS is a rare disease, which is defined by the National Institutes of Health (NIH) as a disease that affects fewer than 200,000 people in the U.S. According to information published by Orphanet, the prevalence of LEMS ranges from 1-9 people per 1 million. Therefore there are an estimated 320 to 3,000 LEMS patients in the U.S. Worldwide, it is estimated that LEMS affects between 21,000 and 28,000 people; making it quite rare.
There are two types of LEMS, paraneoplastic, in which the disease is associated with cancer and non-paraneoplastic with no known underlying cause. Approximately half of LEMS patients have an underlying malignancy that is small cell lung cancer 90% of the time, although other cancers have been reported. It is believed that antibodies that are attacking the cancer become confused and also attack the nerve terminals. Clinical manifestations frequently precede cancer identification. In most cases, the cancer is discovered within the first year after onset of LEMS and, in virtually all cases, within 5 years.” Therefore, it is important for LEMS patients to be periodically screened for lung cancer, even if none is initially found.
What is an Autoimmune Disease?
Autoimmune diseases are a result of a person’s immune system attacking their healthy cells and tissues. As many as 50 million Americans are affected by one of 80 types of autoimmune disorders. There is no known cause, and no cure, but most are treatable. Autoimmune diseases are characterized by periods of flare-ups and remission.
What is a Neuromuscular Disease?*
Neuromuscular diseases affect the peripheral nervous system outside the brain and spinal cord (the central nervous system). Neuromuscular disorders affect the nerves that control voluntary muscles. Voluntary muscles are the ones the body can control, such as those in arms and legs. Nerve cells, also called neurons, send the messages that control these muscles. When the neurons become unhealthy or die, communication between the nervous system and muscles breaks down. As a result, muscles weaken and waste away. The weakness can lead to twitching, cramps, aches and pains, and joint and movement problems. Sometimes it also affects heart function and the ability to breathe. Many neuromuscular diseases are genetic, which means they run in families or there is a mutation in the genes. Sometimes, an immune system disorder can cause them. Most of them have no cure. Generally, the goal of treatment is to improve symptoms, increase mobility and lengthen life. Examples of neuromuscular disorders include multiple sclerosis, spinal muscle atrophy, and myasthenia gravis.
LEMS is a type of neuromuscular disease that affects the communication between the nerve and the muscle and therefore shares some similarities with the more common myasthenia gravis (MG). However, LEMS is 10 times less common than MG, and the pathology differs. The first symptoms of LEMS are usually leg weakness and difficulty walking. Oculobulbar weakness (affecting the muscles of the eyes, face and throat) may occur later, causing ptosis (droopy eyelids), speech impairment and swallowing problems. LEMS patients typically experience weakness of the eye muscles and muscles involved in talking, swallowing and chewing. LEMS also sometimes causes autonomic (involuntary) symptoms such as dry mouth, constipation, impotence and bladder urgency.
What is Small Cell Lung Cancer?
Small cell lung cancer represents about 15% of all lung cancers. It can spread quickly and although it responds to chemotherapy, it can reoccur. Early detection is key to long-term positive outcomes. The lung cancer in LEMS patients may have a better prognosis than in those without LEMS, possibly due to earlier detection.
*Material modified and sourced from www.mda.org.