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  1. 1. Title: MYASTHENIA GRAVIS1MYASTHENIA GRAVIS2Myasthenia gravisA neuromuscular disorderCharacterized1) abnormal fatigability of voluntary muscleon repetitive activity and recover by rest.2) electrophysiologicallydecrementalresponse to repetitive stimulation bysingle-fiber electromyography.3Myasthenia gravis3) improve by administration ofanticholinesterase drugs.4) association with abnormality of thymus.5) presence of circulating antibody to AChRs andcomplement-mediated damage to receptor.4Clinical pictureInvolvement of various voluntary muscle group.Abnormal fatigability on repetitive activity withimprovement after rest.Progressive worsening symptoms through the dayfrom morning to evening.Ocular symptoms as diplopia and ptosisWeakness and fatigue transiently.5Clinical pictureBulbar innervated musculature is affecteddysphagia dysarthria difficult in masticationfailure of respiratory muscle.Most serious symptoms are ventilatory failure.In women the symptoms may affected bypregnancy menses and stress.7ElectrophysiologySingle fiber electromyography.Record the jitter phenomenon.Jitter is variable temporal separation of theresponse of individual muscle fibers of the samemotor unit during activation.Abnormally variable separation may found morethan 80 patients with myasthenia gravis.
  2. 2. 8Pharmacologic treatmentLoewi(1932)noted acetylcholine is neuromusculartransmission in cardiac muscle Sir HenryDale(1935)noted acetylcholine is liberated atmotor nerve ending in voluntary striatedmuscle1936 Nobel prize.Propagation of action potential down a motornerve fiber release acetylcholine from synapticvesicles depolarization muscle.10Pharmacologic treatmentOnly a small fraction of the 30-40 millionreceptors per neuromuscular junction areactivated normally in response to a nerveimpulse.The receptors excess provide large safety ensurethe repetitively neuromuscular transmission.11Pharmacologic treatmentAnticholinesterasephysostigmineneostogminepyridostigmine block the cholinesteraseinactivation of acetylcholineTensilon(edrophonium chloride) testrapid actionand rapid subsidence a basic diagnostic test.12Pathogenesis and immunobiologySimpson (1960) Autoimmune origin.Almon (1974) Demonstrate circulation antibodiesto AChR site of neuromuscular junction.13Pathogenesis and immunobiologyThree possible mechanism1)Accelerating the degradation ofanticholinesterase receptor through thecross-linking phenomenon.2)Direct blocking receptor site.3)Actual degradation the receptor site bycomplement activation.14Pathogenesis and immunobiology
  3. 3. Elevated antibody level are found in 90 patientand roughly correlated with clinical severity.Immunosuppressive agents as azathioprinecorticosteroid cyclosporine may have benefiteffect.15PathologyThymoma is present in 10-15 patient withmyasthenia gravis.Normal 10-25.Other is thymic hyperplasia.16ThymectomyVon Haberer 1917 transcervicalthymectomybecause of thymic hyperplasia often found inthyrotoxicosis.Blablock 1936 upper sternotomy incision andintroduced neostigmine the operation is success.17ThymectomyCarlens (1968) Crile (1965) Akakura (1965)re-describe the old technique of transcervicalthymectomy.Papatestas (1987) perform more than 700transcervicalthymectomy.Incomplete thymectomy is the most importantproblem.18ThymectomyAdvantage of transcervical incision incisiononly involve soft tissue rarely enter thepleural space well tolerated by patients.Cooper (1988) add self-retaining retractor toaid in transcervical exposure and able to extenttransternal resection.
  4. 4. Type of surgical exposure is most importantdeterminant of the extent of resection.19Thymoma10-15 patient with MG has thymoma.30-50 thymoma are associated with MG.20ClassificationsModified Osserman and Genkin classification.Oosterhuis classification.Result classification.Immunobiological classification.24Present indications for thymectomyPatient with thymoma the thymectomy isindicated all.If no thymoma the patient age symptomsduration severity response to medication sexare factors in decision-making.The ocular type may try medical therapy for ayear and if the symptoms interfere the dailylife the thymectomy should be considered.High incidence of unsuspected thymoma in patientolder than 40y/o with ocular symptom only.27ResultAdult patient without thymoma undergoingthymectomy has higher incidence of completeremission.Complete remove all thymic tissue fommediastiumand lower neck from standard transternal incisionis required in surgical treatment of myastheniagravis.