Myasthenia Gravis
Myasthenia gravis (MG) is a rare autoimmune neuromuscular
junction (where a nerve cell meets a muscle cell) disorder caused as a result of
problems in the transmission of nerve signals to muscles. MG
is primarily characterized by muscle weakness and
muscle fatigue. In
general population MG affects
10 - 20 in 1,00,000 (approaching 0.02%) people.
Normally, nerve endings release a substance, called
acetylcholine, which binds to receptors, called acetylcholine receptors, on
muscles. That binding signals muscles to contract. In an MG person, body's own
immune system makes blocking molecules, known as antibodies, to block binding
signal. In other words MG interferes with messages nerves send to muscles.
Common symptoms are trouble with vision (diplopia)
and eyelid movement (ptosis), facial expression and swallowing (dysphagia) and
general muscle fatigue.
Treatment may include symptomatic treatment with cholinesterase inhibitors
and modulation of the immune system with corticosteroids etc. Improvement may be
achieved with plasma exchange or intravenous immunoglobulin in specific cases.
Removal of thymus gland (thymectomy) is also an option.
As back as 17th century there were a few reports of heavy eye lids
and fatiguable weakness. Nineteenth century witnessed modern description of
myasthenic symptoms. In 1930s thymectomy was established as an effective
treatment for MG.
Contributor:
Duraiswamy Navaneetham PhD.
Temple University School of Medicine
Philadelphia, PA, USA
October 2009
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