Myasthenia Gravis

1. Myasthenia Gravis

2. 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.

3. 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.

4. 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.

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

6. 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.

7. 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.

10. 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.

11. 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.

12. 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.

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

14. 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.

15. Myasthenia Gravis: Clinical Features • Ocular manifestations • – Ptosis, uni- or bilateral is very common and may occur while patients reading, or during long period of driving

16. Ptosis

17. 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

18. Up to 75% of Pt’s have abnormality of thymus • 25% have thymoma, tumor (either benign or malignant) of thymus

19. 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 weaker than neck extension

20. Medications induce MG • Possible association • – Anticholinergic drugs (artane); • – Anti-infectives (ampicillin, imipenem, erythromycin) • – Cardiovascular drugs (propafenoneHCl, verapamil); • – Cholroquinephosphate • – Neuromuscular-blocking drugs (vecuronium, • succinylcholine)

21. 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

22. Myasthenia Gravis: Treatment • The goal is to achieve remission By increased neuromuscular transmission • Reduce autoimmunity

23. 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

24. 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

25. Before and after treatment

26. 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.

27. Myasthenia crisis • Management • – Stop every medications • – Assisted ventilation

28. Drugs to watch out for as a medic • Vecuronium • Succinylcholine • Fentanyl

29. References • Www.ctsnet.org/doc/4989 • http://www.myasthenia.org/amg_whatismg.cfm • http://en.wikipedia.org/wiki/Myasthenia_gravis • http://www.nlm.nih.gov/medlineplus/myastheniagravis.html • http://www.sfn.org/index.cfm?pagename=brainBriefings_MyastheniaGravis