Answer: Lambert Eaton myasthenic syndrome is a rare motor disease that results in muscle weakness.
Lambert Eaton myasthenic syndrome, or LEMS, is a neuromuscular disorder. It is a rare disease, affecting an estimated 3 people per million. The disease is progressive and neurodegenerative, with symptoms getting worse over time. In about 60% of cases, LEMS is seen in conjunction with some form of cancer, most often with small-cell lung cancer.
Symptoms
People with LEMS have significant weakness in their proximal limbs, initially appearing in the upper legs and hips. This can result in difficulty walking. As the disease progresses, patients begin to experience weakness in their upper limbs as well, including the arms and shoulders. It can also result in weakness of the eye or facial muscles. When the muscles that control eye movement function improperly, a person may report diplopia, or double vision, since the eyes are unable to properly focus onto a single object in the visual field.
Sometimes, there are also autonomic nervous system deficits in Lambert Eaton syndrome, such as dry mouth.
The age of onset of LEMS is generally in a person's 60s. However, there are rare genetic forms of the disease that cause the onset of symptoms to happen in a person's 30s, but these cases are much more rare.
Cause of Lambert Eaton myasthenic syndrome
The main theory behind the symptoms of Lambert Eaton myasthenic syndrome is an autoimmune-based theory. It is thought that the body begins producing antibodies against voltage-gated calcium channels, which causes the immune system to destroy these ion channels. Voltage-gated calcium channels, or VGCCs, are very important for proper muscle activity. They are expressed heavily on the axon terminals of motor neurons at the neuromuscular junction. When an action potential travels down the axon and reaches the terminal, the depolarization causes the VGCCs to change configuration and open. Once these channels open, calcium is able to move down the electrochemical gradient, rushing into the cell. Calcium ions at the terminal are important since calcium is used to allow for vesicular fusion, thus allowing for the release of acetylcholine into the synapse. This neurotransmitter is excitatory at the muscles, and is the signal for muscle contraction, which leads to movement.
Because of the deficient calcium entry in axons, people with LEMS are sometimes able to overcome their motor deficits by repeatedly using the affected muscles. Frequent activity will cause an accumulation of terminal calcium, which can allow for release of acetylcholine.