Understanding Lambert-Eaton Syndrome


Lambert-Eaton syndrome is caused when your immune system produces antibodies that reduce nerve cell-muscle fiber communication. Specifically, antibodies target voltage-gated calcium channels on presynaptic nerve terminals and prevent the release of the neurotransmitter acetylcholine. The condition is known as either paraneoplastic or non-paraneoplastic. Patients with paraneoplastic LEMS have an underlying malignancy, and the onset of weakness typically precedes cancer diagnosis.


What is Lambert-Eaton Syndrome? Lambert-Eaton syndrome happens when your body’s immune system mistakenly attacks the contact point between motor nerves and muscles — the neuromuscular junction. This reduces the strength of signals sent from the nerves to the muscles, causing weakness. It most often affects the muscles in your legs, hips, and arms — including those you use to walk, climb stairs, and lift things. It also can weaken the muscles involved in breathing, swallowing, and speech. It’s unclear why some people develop this condition, but it’s associated with cancer and other autoimmune disorders like myasthenia gravis. The first step in treating Lambert-Eaton syndrome is to treat the cancer that caused it. Your healthcare provider may prescribe chemotherapy, surgery, or other treatments for the cancer. These treatments may improve the symptoms of Lambert-Eaton syndrome, too. Other medicines help strengthen the signals sent between your nerves and muscles.


In LEMS, your immune system produces antibodies that attack the neuromuscular junctions. These are areas where your nerve cells connect to your muscle cells and help your muscles move. Lambert-Eaton syndrome impairs this function and causes muscle weakness. This condition is often associated with a type of cancer known as small-cell lung cancer and may result from your body’s efforts to fight the underlying tumor. In some cases, it occurs without known cancer and is called paraneoplastic neuropathy. Symptoms of LEMS begin gradually and include weakness as well as fatigue. The weakness affects both your voluntary muscles – those you control – and your autonomic nervous system muscles that help regulate breathing and blood pressure. Weakness is felt mainly in your legs, arms, chest, neck, and abdomen. In some people, this weakness is accompanied by a dry mouth or drooping eyelids and may worsen by heat or exercise. A physical exam and tests such as electromyography (EMG) and nerve conduction studies confirm the diagnosis. Treatment aims to treat the underlying cancer and relieve the symptoms of Lambert-Eaton syndrome. Antidepressants and drugs that increase the release of acetylcholine may improve symptoms. Plasma exchange, in which a sample of your blood is removed and replaced with healthy plasma, can also help some people.


LEMS is caused by your immune system mistakenly attacking the connection between nerves and muscles (neuromuscular junction). Your body’s natural defenders release proteins that attack these connections, specifically targeting calcium channels on nerve endings. These channels are necessary to release acetylcholine, which triggers muscle contraction. When the release of acetylcholine is blocked, you feel weak. You can get LEMS as part of a paraneoplastic syndrome associated with cancer (CA-LEMS), or you can have it without cancer as an autoimmune condition (NCA-LEMS). Suppose you have a high risk for the disease. In that case, your healthcare provider will examine you and may order a particular blood test to check for antibodies that attack the neuromuscular junctions. Your doctor will also do a physical exam to see if your muscles are weak. They will also ask about your symptoms and history. They may do an electromyography test to measure how fast signals travel from your brain to your muscles. This will help your doctor rule out another autoimmune disorder that affects the nerves and muscles, myasthenia gravis. Your doctor will prescribe medicine to reduce the symptoms of this condition. They will start with a medication that promotes the production of acetylcholine in the body, which should improve your strength and help you walk better. They might also prescribe drugs that suppress the immune system or strengthen the signals between nerves and muscles.


While it isn’t known what causes LEMS, it’s thought that the immune system mistakenly attacks the place where nerve cells meet muscle fibers (neuromuscular junction). The antibodies in this condition target calcium channels at the end of the nerve cells. The antibodies stop these channels from opening, meaning fewer signals reach the muscle cells to make them contract. This can lead to weakness of the legs, arms, and face. Symptoms generally occur slowly over weeks or months and can worsen if cancer is present. Most people with this condition have small-cell lung cancer, but it can also happen with other types of cancer. The connection is likely because cancer and LEMS have the same type of calcium channel at their end. The immune system responds to these calcium channels by releasing proteins that attack cancer cells and damage some nerve cell membranes that connect to the muscles. While it’s unknown what can prevent the onset of LEMS, some health experts recommend not smoking and regular checkups to look for cancer. Cancer treatment can help to improve symptoms of the disease. Doctors can also prescribe medicines to suppress the immune system or improve nerve and muscle cell signals. In some cases, high doses of immunoglobulins can also be used to treat the disease.