Myasthenia Gravis

Myasthenia gravis is a chronic autoimmune neuromuscular disease that is characterized by different degrees of weakness of the skeletal muscles of the body. The name myasthenia gravis came from a Latin and Greek origin meaning grave muscle weakness.

Myasthenia Gravis is termed an autoimmune disease. The immune system usually makes antibodies to attack bacteria, viruses and germs. With the autoimmune disease, the immune system makes antibodies against parts of ones own body tissues.

Although there is no direct cause known for why the body starts to produce the antibodies that destroy the acetylcholine receptors, it is believed to be related to the thymus gland since it also produces antibodies.

Onset usually occurs in women in the 18-25 year rage and men in the 60-80 year rangeMyasthenia gravis affects approximately 20 in 100,000 people

In a person with normal immune system, muscles are stimulated to contract by the transmission of nerve impulses to the muscle fibers. The nerve impulses cause neurotransmitter acetylcholine to be released into the synaptic cleft. There it is picked up by the acetylcholine receptors on the muscle fiber.

In myasthenia gravis, the numbers of acetylcholine receptors appear to be reduced. There is evidence to indicate that the receptor deficit is caused by an attack on the acetylcholine receptors by the body's own immune system.

With the numbers of acetylcholine receptors reduced, it causes the nerve impulse to be prevented from reaching the muscles. The result is weakness and rapid fatigue only in the affected muscles.

About 60 % patients have weakness in the eye muscles, termed ocular myasthenia. The majority of other patients will go on to develop weakness in other muscle groups.

Other types of myasthenia gravis include congenital MG, which is an inherited condition caused by a genetic defect instead of an immune disorder

It develops in an infant shortly after being born to a mother with myasthenia gravis and usually has generalized symptoms.

Transient neonatal MG is a temporary condition that develops in approximately 10-20% of infants born to a mother with myasthenia gravis

It is caused by the circulation of the mothers antibodies through the placenta and lasts as long as the mothers antibodies remain in the infant.

Myasthenia Gravis: Clinical Features

Ocular manifestations – Ptosis, uni- or bilateral is very

common andmay occur while patients reading, or during long period of driving

Ptosis

Myasthenia Gravis: Clinical Features

Difficulty chewing, speaking, or swallowing:initial symptoms in 17% of patients

Fatigability and weakness during mastication

Unable to keep jaw closed after chewing

Slurred and nasal speech

Up to 75% of Pt’s have abnormality of thymus

25% have thymoma, tumor (either benign or malignant) of thymus

S/S

Limb muscles weakness: – Initial symptoms in fewer than 10% – Upper extremities weakness is more

common than lower extremities,asymmetrical

– Involve proximal muscles than distal – Involve neck muscles: neck flexion

weakerthan neck extension

Medications induce MG

Possible association – Anticholinergic drugs (artane); – Anti-infectives (ampicillin, imipenem,

erythromycin) – Cardiovascular drugs (propafenone

HCl, verapamil); – Cholroquine phosphate – Neuromuscular-blocking drugs

(vecuronium,succinylcholine)

www.ctsnet.org/doc/4989 • Osserman Classification Grade I: involve focal disease (restricted

to ocular muscle) Grade II: generalized disease IIa: mild IIb: moderate Grade III: severe generalized disease Grade IV: a crisis with life-threatening

impairment of respiration

Myasthenia Gravis: Treatment

The goal is to achieve remission By increased neuromuscular

transmission Reduce autoimmunity

TX

blood tests are done to detect the abnormal antibody that destroys the receptors

If spread out, in 2 y – thymectomy Acetylcholine-receptor antibody levels fall

Immunosuppressive therapy Cyclosporine Inhibits T-cell activation

How to detect

Electromyography Repetitive Nerve Stimulation to check for a post-synaptic defect or a muscle biopsy to look for antibodies may also be used.

• Serologic tests(test clear portion of the blood) may be used

• Chest x-ray

Before and after treatment

MG is usually not fatal but in the case of a myasthenia crises occurrence (when muscles needed for breathing are affected), hospitalization and intensive care may be necessary to aid breathing with a respirator.

Myasthenia crisis

• Management – Stop every medications – Assisted ventilation

Drugs to watch out for as a medic

Vecuronium Succinylcholine Fentanyl

References

Www.ctsnet.org/doc/4989http://www.myasthenia.org/amg_

whatismg.cfmhttp://en.wikipedia.org/wiki/Mya

sthenia_gravishttp://

www.nlm.nih.gov/medlineplus/myastheniagravis.html

http://www.sfn.org/index.cfm?pagename=brainBriefings_MyastheniaGravis