Lambert–Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder that is characterised by muscle weakness of the limbs. It is the result of an autoimmune reaction, where antibodies are formed against voltage-gated calcium channels in the neuromuscular junction, the connection between nerves and the muscle that they supply. Around 60% of those with LEMS have an underlying malignancy, most commonly small cell lung cancer; it is therefore regarded as a paraneoplastic syndrome (a condition that arises as a result of cancer elsewhere in the body).
People who develop LEMS are usually over 40, although it may occur at any age. The diagnosis is usually confirmed with electromyography and blood tests; these also separate it from myasthenia gravis, a related autoimmune neuromuscular disease.
If the disease is associated with cancer, direct treatment of the cancer often relieves the symptoms of LEMS. Other treatments often used are steroids, azathioprine and intravenous immunoglobulin, which suppress the immune system, and pyridostigmine and 3,4-diaminopyridine, which enhance the neuromuscular transmission. Occasionally, plasma exchange is required to remove the antibodies.
Signs and symptoms
The weakness of LEMS typically involves the legs and arms. Leg involvement is more striking than in myasthenia gravis. The proximal muscles (those closest to the trunk) are predominantly affected; this leads to difficulties climbing stairs and rising from a sitting position. Physical exercise and high temperatures can worsen the symptoms. Weakness of the bulbar muscles (supplying the mouth and throat) is occasionally encountered. Weakness of the eye muscles is uncommon, but double vision, drooping of the eyelids and difficulty swallowing are occasionally encountered, but generally only together with leg weakness; this distinguishes LEMS from myasthenia gravis, in which eye signs are much more prominent. In the advanced stages of the disease, weakness of the respiratory muscles may occur. Some may also experience problems with coordination (ataxia).
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