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MYASTHENIA GRAVIS

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1) abnormal fatigability of voluntary muscle on repetitive ... Ocular symptoms as diplopia and ptosis, Weakness and fatigue transiently. Clinical picture ... – PowerPoint PPT presentation

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Title: MYASTHENIA GRAVIS


1
MYASTHENIA GRAVIS
  • GENERAL THORACIC SURGERY
  • CHAPTER 168

2
Myasthenia gravis
  • A neuromuscular disorder,
  • Characterized
  • 1) abnormal fatigability of voluntary muscle
    on repetitive activity, and recover by rest.
  • 2) electrophysiologically decremental
    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.

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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.

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.

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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
  • Anticholinesterasephysostigmine, neostogmine,
    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
  • 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 transcervical thymectomy
    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
    transcervical thymectomy.
  • 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.
  • 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.

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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.

25
Present indications for thymectomy
  • Thymectomy is not recommended for the neonatal
    type of myasthenia gravis.
  • In juvenile form the reserve thymectomy for
    patient with more severe symptoms and lack of
    response to medical therapy.

26
Present indications for thymectomy
  • In adult Cooper, Jaretzki and Papatestas all
    believed patient with general symptoms should
    receive early thymectomy as soon as the diagnosis
    established.
  • 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 fom mediastium
    and lower neck from standard transternal incision
    is required in surgical treatment of myasthenia
    gravis.

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