Myasthenia gravis (MG) is a chronic disorder
with symptoms of weakness and
rapid fatigue of any of the muscles that are under your voluntary control. It’s
caused by a breakdown in the normal communication between nerves and
muscles. It is a chronic autoimmune disorder that results in progressive skeletal
MMG causes rapid fatigue and loss of strength
upon exertion that improves after rest.
Myasthenia gravis is caused by a defect
in the transmission of nerve impulses to muscles. Usually when impulses travel
down the nerve, the nerve endings release a neurotransmitter substance called acetylcholine.
In myasthenia gravis, antibodies produced by the body’s own
immune system block, alter or destroy the receptors for acetylcholine.
MG is associated with other autoimmune
diseases. Patients who have family members suffering from disorders such as
rheumatoid arthritis, scleroderma,
lupus may have an increased risk for
Approximately 15% of MG patients have a tumor of the thymus
(also called as thymoma) and 60–80% have abnormal enlargement (hyperplasia) of
the thymus. The thymus produces cells involved in immune
responses and is located below the larynx and above the heart.
Myasthenia gravis affects
approximately 2 out of every 100,000 people and can occur at any age. It is most
common in women between the ages of 18 and 25. In men, the condition usually
develops between 60 and 80 years of age.
Myasthenia gravis can be
classified according to which skeletal muscles are affected.
Generalized MG: Within
a year of onset 85–90% of patients develop generalized MG, characterized by weakness in the trunk, arms and legs.
10–15% of patients have
weakness only in muscles that control eye movement. This type is
called ocular myasthenia gravis.
Other types of MG include congenital, which is an inherited condition caused
by genetic defect and occurs in infants born to
mothers who have MG. Congenital MG develops at or shortly after birth and
causes generalized symptoms.
Transient Neonatal MG: A
temporary condition that develops in 10–20% of infants born to mothers who
have MG. Transient neonatal MG is
caused by circulation of the mother’s antibodies through the placenta and it
lasts as long as the mother’s antibodies remain in the infant (usually a few
weeks after birth).
Myasthenia gravis symptoms can be
controlled but not cured with medical treatment.
Some medications like
cholinesterase inhibitors, such as pyridostigmine (Mestinon) and corticosteroids improve neuromuscular
transmission and increase muscle strength, and some suppress the production
of abnormal antibodies.
These medications must be used
with careful medical follow-up because they may cause major side effects.
Thymectomy the surgical
removal of the thymus gland (which often is abnormal in myasthenia gravis
patients), improves symptoms in certain patients and may cure some
individuals, possibly by re-balancing the immune system.
Other therapies include
plasmapheresis which a procedure in which abnormal antibodies are removed from
High-dose intravenous immune
globulin (IVIG), which temporarily modifies the immune system and provides the body
with normal antibodies from donated blood.