1. Title: MYASTHENIA GRAVIS
1
MYASTHENIA GRAVIS
2
Myasthenia gravis
A neuromuscular disorder
Characterized
1) abnormal fatigability of voluntary muscle
on repetitive activity and recover by rest.
2) electrophysiologicallydecremental
response to repetitive stimulation by
single-fiber electromyography.
3
Myasthenia gravis
3) improve by administration of
anticholinesterase drugs.
4) association with abnormality of thymus.
5) presence of circulating antibody to AChRs and
complement-mediated damage to receptor.
4
Clinical picture
Involvement of various voluntary muscle group.
Abnormal fatigability on repetitive activity with
improvement after rest.
Progressive worsening symptoms through the day
from morning to evening.
Ocular symptoms as diplopia and ptosis
Weakness and fatigue transiently.
5
Clinical picture
Bulbar innervated musculature is affected
dysphagia dysarthria difficult in mastication
failure of respiratory muscle.
Most serious symptoms are ventilatory failure.
In women the symptoms may affected by
pregnancy menses and stress.
7
Electrophysiology
Single fiber electromyography.
Record the jitter phenomenon.
Jitter is variable temporal separation of the
response of individual muscle fibers of the same
motor unit during activation.
Abnormally variable separation may found more
than 80 patients with myasthenia gravis.

2. 8
Pharmacologic treatment
Loewi(1932)noted acetylcholine is neuromuscular
transmission in cardiac muscle Sir Henry
Dale(1935)noted acetylcholine is liberated at
motor nerve ending in voluntary striated
muscle1936 Nobel prize.
Propagation of action potential down a motor
nerve fiber release acetylcholine from synaptic
vesicles depolarization muscle.
10
Pharmacologic treatment
Only a small fraction of the 30-40 million
receptors per neuromuscular junction are
activated normally in response to a nerve
impulse.
The receptors excess provide large safety ensure
the repetitively neuromuscular transmission.
11
Pharmacologic treatment
Anticholinesterasephysostigmineneostogmine
pyridostigmine block the cholinesterase
inactivation of acetylcholine
Tensilon(edrophonium chloride) testrapid action
and rapid subsidence a basic diagnostic test.
12
Pathogenesis and immunobiology
Simpson (1960) Autoimmune origin.
Almon (1974) Demonstrate circulation antibodies
to AChR site of neuromuscular junction.
13
Pathogenesis and immunobiology
Three possible mechanism
1)Accelerating the degradation of
anticholinesterase receptor through the
cross-linking phenomenon.
2)Direct blocking receptor site.
3)Actual degradation the receptor site by
complement activation.
14
Pathogenesis and immunobiology

3. Elevated antibody level are found in 90 patient
and roughly correlated with clinical severity.
Immunosuppressive agents as azathioprine
corticosteroid cyclosporine may have benefit
effect.
15
Pathology
Thymoma is present in 10-15 patient with
myasthenia gravis.
Normal 10-25.
Other is thymic hyperplasia.
16
Thymectomy
Von Haberer 1917 transcervicalthymectomy
because of thymic hyperplasia often found in
thyrotoxicosis.
Blablock 1936 upper sternotomy incision and
introduced neostigmine the operation is success.
17
Thymectomy
Carlens (1968) Crile (1965) Akakura (1965)
re-describe the old technique of transcervical
thymectomy.
Papatestas (1987) perform more than 700
transcervicalthymectomy.
Incomplete thymectomy is the most important
problem.
18
Thymectomy
Advantage of transcervical incision incision
only involve soft tissue rarely enter the
pleural space well tolerated by patients.
Cooper (1988) add self-retaining retractor to
aid in transcervical exposure and able to extent
transternal resection.

4. Type of surgical exposure is most important
determinant of the extent of resection.
19
Thymoma
10-15 patient with MG has thymoma.
30-50 thymoma are associated with MG.
20
Classifications
Modified Osserman and Genkin classification.
Oosterhuis classification.
Result classification.
Immunobiological classification.
24
Present indications for thymectomy
Patient with thymoma the thymectomy is
indicated all.
If no thymoma the patient age symptoms
duration severity response to medication sex
are factors in decision-making.
The ocular type may try medical therapy for a
year and if the symptoms interfere the daily
life the thymectomy should be considered.
High incidence of unsuspected thymoma in patient
older than 40y/o with ocular symptom only.
27
Result
Adult patient without thymoma undergoing
thymectomy has higher incidence of complete
remission.
Complete remove all thymic tissue fommediastium
and lower neck from standard transternal incision
is required in surgical treatment of myasthenia
gravis.