Myasthenic Myopathic Syndrome of Lambert Eaton, also known as Lambert-Eaton myasthenic syndrome (LEMS), is a rare autoimmune disorder characterized by muscle weakness and reduced nerve signal transmission. This neurological disorder affects the neuromuscular junction, the area where nerve cells connect to muscle cells, leading to impaired muscle movement and function.
The underlying cause of LEMS is an autoimmune response in which the body's immune system mistakenly attacks the voltage-gated calcium channels (VGCCs) on the nerve cells. These channels play a vital role in transmitting electrical signals between nerve cells and muscles, facilitating muscle contractions. The autoantibodies produced in LEMS bind to these channels, reducing the release of a neurotransmitter called acetylcholine. As a result, there is a decrease in the amount of acetylcholine available to stimulate muscle contraction.
The most common symptoms of LEMS include muscle weakness and fatigue, particularly in the proximal muscles of the limbs. Other symptoms may include difficulty in walking, climbing stairs, and maintaining posture. The weakness typically improves with exercise due to increased acetylcholine release during muscle activity.
LEMS is often associated with an underlying malignancy, most commonly small cell lung cancer. Diagnosis of LEMS involves a combination of clinical evaluation, electromyography (EMG), and blood tests to detect autoantibodies against the VGCCs.
Treatment options for LEMS include medications that enhance acetylcholine release from nerve cells, such as pyridostigmine and 3,4-diaminopyridine, which can improve muscle strength and function. Additionally, immunosuppressive therapies, such as corticosteroids or intravenous immunoglobulin, may be used to suppress the autoantibody production.
