文档介绍：Muscular diseases Myasthenia gravis
Definition: Myasthenia gravis is caused by a defect of neuromuscular transmission due to an antibody-mediated attack upon nicotinic acetylcholine receptors(AChR).
Clinical Character:
Fluctuating weakness
Improved by inhibitors of cholinesterase
Etiology and Pathogenesis
Related to destructive effects of autoantibodies to AChR
Evidence:
1. Experimental immunization of animals with purified AChR from an electric fish, induces high titers of antibody to the receptor.
2. Human serum antibodies that react with human AChR were found in MG patients
features of MG were produced by passive transfer of human IgG to mice.
4. Plasmapheresis reduced plasma levels of anti-AChR and ameliorated myasthenic symptoms and signs.
How the autoimmune disorder starts is not known.
In human MG, hyperplasia of the thymus
about 15% of cases is a thymoma.
AChR antibodies are synthesized by B cell of hyperplastic thymus gland.
When human myasthenic thymus was transplanted into mice, the animal produced antibodies to AChR that bound to their own motor end-plates.
A.   Primarily in the thymus.
1. 70% of thymus gland from adult MG patients are not involuted.
2.    The thymus weigh more than normal.
3. The thymus glands show lymphoid hyperplasia.
4. Immunocytochemical:germinal centers contain B cells, plasma cells, and T cells.
Pathology
5. 10% of myasthenic thymus glands contain thymomas.
B. Loss of synaptic folds and widened clefts
C. Some nerve terminals are smaller than normal.
D. On residual synaptic folds show Y-shaped antibody-like structures, IgG.
Clinical features
1. Incidence: ,000.
Prevalence: 5/100,000.
Before age 40, Male:female 3:1
2. Symptoms: Three clinical characteristics.
1) The fluctuating nature : The weakness varies in a single day; day to day; or over longer periods.(remissions or exacerbations).
Crisis: When an exacerbation involves respiratory muscles
2) The distribution of weakness