Lambert-Eaton myasthenic syndrome (LEMS) is a rare disorder in which the immune system attacks certain molecules on nerve cells that control muscle movements. As a result, nerve cells are unable to send proper signals instructing muscles to contract, which is what ultimately causes the disease’s symptoms.
Those symptoms can include muscle weakness, fatigue, lack of reflexes, and vision, speech, and swallowing problems. Breathing problems may occur, as may issues with other autonomic processes, such as digestion and coordination.
LEMS symptoms tend to be mild initially and then gradually worsen over time. Symptoms tend to worsen faster in cases in which LEMS is associated with cancer.
The most common symptom of LEMS is muscle weakness, resulting from the lack of nerve signals instructing muscles to contract. In addition to feeling physically weaker, patients also may also feel unusually stiff.
Usually, the most affected muscles in LEMS are the proximal muscles — those in the shoulders, hips, and upper legs — which are closer to the body’s trunk. For example, many people with LEMS will experience difficulty walking, or rising from a seated position, owing to weakness in the hip and upper leg muscles.
As the disease progresses, weakness may spread out to distal muscles — those farther from the body’s trunk — in the lower arms and legs.
Related to muscle weakness, many people with LEMS experience fatigue, or feeling unusually tired, even after a good night’s sleep. This commonly manifests as a person feeling substantially more tired than they normally would after performing day-to-day activities.
Lack of reflexes
In another symptom related to muscle weakness, many people with LEMS will lack or have poor tendon reflexes upon physical examination. A particular finding common in LEMS is “postexercise facilitation,” a phenomenon in which tendon reflexes and muscle strength improve after a period of repeated muscle contraction.
Vision, speech, and swallowing problems
While LEMS mainly affects the limbs, in more than two-thirds of patients, it also affects nerves in the face.
This can cause weakness in the muscles that are responsible for controlling eye and eyelid movements. As a result, people with LEMS may experience vision problems and other eye-related symptoms. Double-vision, called diplopia, and eyelid droopiness, known as ptosis, are among the most common eye-related manifestations of LEMS.
LEMS also can cause weakness in the muscles that control the tongue and jaw, which can lead to speech difficulties. Known as dysarthria, speech problems due to muscle weakness often manifest with speech that is abnormally slow, quiet, or slurred. Weakness in the jaw and throat also can cause difficulty swallowing, a condition known as dysphagia.
The autonomic nervous system is the part of the nervous system that controls unconscious bodily processes, such as digestion, breathing, and sex drive. While LEMS primarily damages nerve cells that control muscle movements, it also can damage nerves in the autonomic nervous system, resulting in autonomic dysfunction or impairments.
Common manifestations of autonomic dysfunction in LEMS include dry mouth, dry eyes, constipation, sweating less than normal, and erectile dysfunction.
In severe cases, LEMS can cause weakness in the muscles that are involved in breathing. At later stages, this may lead to respiratory failure — a condition in which body tissues are not receiving enough oxygen.
Last updated: Oct. 21, 2021
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