Myasthenia: from the Greek words, myelos, meaning muscle,
and astheneia, meaning weakness
Gravis: from the Latin word, gravidus, meaning heavy
(serious)
Myasthenia gravis (MG) is an autoimmune disease that is
characterized by impairment of motor nerve impulses causing
episodic muscle weakness and fatigue, especially in the
face, tongue, neck, and respiratory muscles. MG occurs at
all ages, usually between the ages of 20 and 40, sometimes
in association with a thymic tumor or thyrotoxicosis, as
well as in rheumatoid arthritis and lupus erythematosus. It
is most common in young women with HLA-DR3; if thymoma
(tumor) is associated, older men are more commonly affected.
Onset is usually insidious, but the disorder is sometimes
unmasked by a coincidental infection that leads to
exacerbation of symptoms. Exacerbations may also occur
before the menstrual period and during or shortly after
pregnancy.
Symptoms
Symptoms are due to a variable degree of neuromuscular
transmission blockage caused by autoantibodies binding to
acetylcholine receptors. These autoantibodies are found in
most patients with the disease and have a primary role in
reducing the number of functioning acetylcholine receptors.
Additionally, cellular immune activity against the receptor
is found. Clinically, this leads to weakness, and initially
powerful movements fatigue readily. The external ocular
muscles and certain other cranial muscles, including the
masticatory, facial, and pharyngeal muscles, are especially
likely to be affected, and the respiratory and limb muscles
may also be involved. In the ocular variety, there is
difficulty with movements of the lids and the eyeball
itself. When the pharyngeal muscles are involved, difficulty
in swallowing ensues.
Only voluntary (or striated) muscles are affected;
involuntary heart muscle and smooth muscle of the gut, blood
vessels, and uterus are not involved. Muscles of the limbs
may also be affected in some MG patients. Asymmetrical
weakness may occur, with one side of the body more affected
than the other. Difficulty may be encountered with simple
tasks such as combing one's hair, shaving, and putting on
makeup. Climbing stairs or walking distances may cause the
legs to easily tire. In 10% of the cases, people develop a
weakness of the muscles needed for breathing, a condition
known as myasthenia crisis. Hospitalization and mechanical
breathing assistance may be necessary in such cases. The
disease is painless but may become painful if the patient
goes into spasm as a result of early fatigue. Skin sensation
is preserved.
The effect of pregnancy on MG varies from patient to
patient. Symptoms of the disease may disappear, worsen, or
remain the same during the course of pregnancy. Obstetrical
problems are usually not present because the smooth muscle
of the uterus is unaffected by the disease. During
second-stage labor, when voluntary striated abdominal
muscles are used, weakness becomes noticeable. Pregnant
women with MG may pass affected antibodies through the
placenta to their unborn child. This results in temporary
neonatal myasthenia, in which the infant has muscle weakness
that disappears several days to a few weeks after birth.
Diagnosis
Doctors may suspect MG in anyone with generalized weakness
that increases with the use of affected muscles and recovers
with rest or in anyone presenting with weakness in the
muscles of the eye and face. Since acetylcholine receptors
are blocked in MG, drugs that increase the amount of
acetylcholine--such as edrophonium--can be used as test
drugs, administered intravenously, to see if muscle strength
will temporarily improve. Blood testing for antibodies to
acetylcholine as well as diagnostic measurement of nerve and
muscle function may also be administered. In equivocal
cases, electrophysiological studies testing nerve
transmission and muscle reaction may be helpful. A
computerized axial tomographic (CAT) scan of the chest may
reveal an associated thymoma.
SHORT-TERM CONVENTIONAL TREATMENT
Short-term treatment for MG includes medications to
counteract the symptoms of weakness and muscle fatigue.
Anticholinesterases, such as neostigmine and pyridostigmine,
which boost the levels of acetylcholine by blocking the
enzyme which breaks acetylcholine down, can provide relief
for a few hours. Some patients may show no response or even
become weaker while taking the drug. Ephedrine sulfate may
be used in conjunction with an anticholinesterase for added
strength if patients are not bothered by possible side
effects, such as nervousness and insomnia.
Plasmapheresis is an expensive short-term treatment in which
several liters of blood are removed from the patient,
centrifuged for removal of abnormal antibodies, and returned
intravenously in artificial plasma. This treatment is
considered when short-term improvement is crucial for the
patient. However, the benefits of the procedure may last
only weeks.
High-dose intravenous human immunoglobulin (IVIg) has
emerged as a conventional therapy for various neurologic
diseases. It may be considered the opposite of
plasmapheresis. Rather than expunging the blood of abnormal
antibodies, IVIg floods the body with pooled gamma globulin
antibodies from several donors. Although expensive, IVIg has
become a first-line or adjunctive therapy in the treatment
of diverse autoimmune diseases, including MG. IVIg therapy
has received Food and Drug Administration approval for use
as a maintenance treatment of patients with primary humoral
(blood-based) immunodeficiencies, and as therapy for acute
or chronic autoimmune thrombocytopenic purpura. In
controlled clinical trials, IVIg has been effective in
treating chronic inflammatory demyelinating polyneuropathy.
IVIg also has produced improvement in some patients with MG,
but has had a variable or unsubstantiated benefit in others.
LONG-TERM CONVENTIONAL TREATMENT
Long-term treatment may include removal of the thymus gland.
About 15% of patients with MG are found to have a tumor of
the thymus gland, known as a thymoma. Most thymomas are
benign. Thymectomy has become a common treatment modality
for patients without thymoma. If most of the thymus is
removed, symptoms usually lessen and, in some individuals,
disappear completely. However, the thymus gland is the
master gland of immunity, and removing this gland severely
weakens the body's ability to fight infections and cancer.
Another long-term treatment approach is the use of
immunosuppressive drugs. This group of drugs is used to
suppress the body's immune system, although it is not known
how they work in MG. Prednisone, azathioprine,
cyclophosphamide, and cyclosporine are all immunosuppressive
drugs. While patients may show significant improvement or
drug-dependent remission of symptoms, they must be monitored
closely for undesirable or serious side effects.
NATURAL THERAPY
Etiology
As previously mentioned, MG has been shown to be an
autoimmune disease. This means that the immune system
attacks some of its own body proteins. Specifically, the
transmission of signals from the nerve endings to the muscle
receptors is partly blocked by antibodies. The messenger
chemical or neurotransmitter released as a signal from nerve
endings to muscles is acetylcholine. Acetylcholine molecules
travel the short distance in the gap between nerve ending
and muscle to find a receptor on the motor end plate. When a
sufficient number of acetylcholine molecules are attached to
muscle receptors, there is an electric discharge of the
normal membrane potential and the muscle fiber can contract.
In MG most of the receptors are already occupied by
antibodies; therefore, not enough acetylcholine molecules
find receptors to trigger this discharge and subsequent
muscle contraction. Normally, the acetylcholine is split by
an enzyme (cholinesterase) and, with this, is removed from
the receptor in a fraction of a second. Using
anticholinesterases, drugs that hinder this enzyme,
acetylcholine molecules have more time to find receptors
with an increased chance of leading to a discharge. However,
if too much of this enzyme antagonist is present, the cells
remain discharged for too long and the muscles become
paralyzed. This is a "cholinergic crisis" in which heart and
breathing may stop.
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