Myasthenia gravis
Myasthenia gravis isdisorderneuromuscular transmission leadingfluctuating weaknessfatigue. A myasthenic crisis may give rise togeneralized paralysisassisted ventilation may be required. Itone ofbest known autoimmune disorders andantigensdisease mechanisms have well been identified. Weaknesscaused by circulating antibodies that block acetylcholine receptors atneuromuscular junction.Acetylcholine ischemical substance that sustains muscle contraction by stimulatingmuscle fibers by bindingits receptors. The immunologic reaction against these receptorsconsecutive damage ofneuromuscular endplate give risedeficient stimulationmuscle fibers. Patients frequently presentrestricted movementseye muscleseyelids, difficulty swallowingspeaking, generalized weaknessfatigue. Myasthenia gravisusually treated by cholinesterase inhibitors, immunosuppressive drugs, thymectomyplasma exchange.
Althoughterm gravis means grave, recent developmentsdisease treatment have madeprognosis more favourable. Howeverconsiderable portionpatients still findnecessaryseek admission tointensive care unitsassisted ventilation.
Whatmyasthenia gravis?
Myasthenia gravis ischronic autoimmune neuromuscular disease characterized by varying degreesweakness ofskeletal (voluntary) muscles ofbody. The name myasthenia gravis, whichLatinGreekorigin, literally means "grave muscle weakness." With current therapies, however, most casesmyasthenia gravisnot as "grave" asname implies. In fact, formajorityindividualsmyasthenia gravis, life expectancynot lessened bydisorder.
The hallmarkmyasthenia gravismuscle weakness that increases during periodsactivityimproves after periodsrest. Certain muscles such as those that control eyeeyelid movement, facial expression, chewing, talking,swallowingoften, but not always, involved indisorder. The muscles that control breathingnecklimb movements may also be affected.
Causemyasthenia gravis
Myasthenia graviscaused bydefect intransmissionnerve impulsesmuscles. It occurs when normal communication betweennervemuscleinterrupted atneuromuscular junction -place where nerve cells connect withmusclescontrol. Normally when impulses travel downnerve,nerve endings releaseneurotransmitter substance called acetylcholine. Acetylcholine travels throughneuromuscular junctionbindsacetylcholine receptors whichactivatedgeneratemuscle contraction.
In myasthenia gravis, antibodies block, alter, or destroyreceptorsacetylcholine atneuromuscular junction which preventsmuscle contraction from occurring. These antibodiesproduced bybody's own immune system. Thus, myasthenia gravisan autoimmune disease becauseimmune system - which normally protectsbody from foreign organisms - mistakenly attacks itself.
The role ofthymus glandmyasthenia gravis
The thymus gland, which lies inupper chest area beneathbreastbone, plays an important role indevelopment ofimmune systemearly life. Its cells formpart ofbody's normal immune system. The glandsomewhat largeinfants, grows gradually until puberty,then gets smalleris replaced by fatage. In adultsmyasthenia gravis,thymus glandabnormal. It contains certain clustersimmune cells indicativelymphoid hyperplasia -condition usually found only inspleenlymph nodes during an active immune response. Some individualsmyasthenia gravis develop thymomas or tumors onthymus gland. Generally thymomasbenign, butcan become malignant.
The relationship betweenthymus glandmyasthenia gravisnot yet fully understood. Scientists believethymus gland may give incorrect instructions aboutproduction ofacetylcholine receptor antibodies, thereby settingstage forattack on neuromuscular transmission.
Symptomsmyasthenia gravis
Although myasthenia gravis may affect any voluntary muscle, muscles that control eyeeyelid movement, facial expression,swallowingmost frequently affected. The onset ofdisorder may be sudden. Symptoms oftennot immediately recognized as myasthenia gravis.
In most cases,first noticeable symptomweakness ofeye muscles. In others, difficultyswallowingslurred speech may befirst signs. The degreemuscle weakness involvedmyasthenia gravis varies greatly among patients, ranging fromlocalized form, limitedeye muscles (ocular myasthenia), tosevere or generalized formwhich many muscles - sometimes including those that control breathing -affected. Symptoms, which varytypeseverity, may includedroopingone or both eyelids (ptosis), blurred or double vision (diplopia) dueweakness ofmuscles that control eye movements, unstable or waddling gait, weaknessarms, hands, fingers, legs,neck,changefacial expression, difficultyswallowingshortnessbreath,impaired speech (dysarthria).
Who gets myasthenia gravis?
Myasthenia gravis occursall ethnic groupsboth genders. It most commonly affects young adult women (under 40)older men (over 60), butcan occur at any age.
In neonatal myasthenia,fetus may acquire immune proteins (antibodies) frommother affectedmyasthenia gravis. Generally, casesneonatal myasthenia gravistransient (temporary) andchild's symptoms usually disappear within few weeks after birth. Other children develop myasthenia gravis indistinguishable from adults. Myasthenia gravisjuvenilescommon.
Myasthenia gravisnot directly inherited norit contagious. Occasionally,disease may occurmore than one member ofsame family.
Rarely, children may show signscongenital myasthenia or congenital myasthenic syndrome. Thesenot autoimmune disorders, butcaused by defective genes that control proteins inacetylcholine receptor oracetylcholineterase.
Methodsdiagnosis
Unfortunately,delaydiagnosisone or two yearsnot unusualcasesmyasthenia gravis. Because weakness iscommon symptommany other disorders,diagnosisoften missedpeople who experience mild weakness orthose individuals whose weaknessrestrictedonlyfew muscles.
The first stepsdiagnosing myasthenia gravis includereview ofindividual's medical history,physicalneurological examinations. The signsphysician must look forimpairmenteye movements or muscle weakness without any changes inindividual's abilityfeel things. Ifdoctor suspects myasthenia gravis, several testsavailableconfirmdiagnosis.
A special blood test can detectpresenceimmune molecules or acetylcholine receptor antibodies. Most patientsmyasthenia gravis have abnormally elevated levelsthese antibodies. However, antibodies may not be detectedpatientsonly ocular forms ofdisease.
Another testcallededrophonium test. This approach requiresintravenous administrationedrophonium chloride or Tensilon®,drug that blocksdegradation (breakdown)acetylcholinetemporarily increaseslevelsacetylcholine atneuromuscular junction. In peoplemyasthenia gravis involvingeye muscles, edrophonium chloride will briefly relieve weakness. Other methodsconfirmdiagnosis includeversionnerve conduction study which testsspecific muscle fatigue by repetitive nerve stimulation. This test records weakening muscle responses whennervesrepetitively stimulated,helpsdifferentiate nerve disorders from muscle disorders. Repetitive stimulation ofnerve duringnerve conduction study may demonstrate decrements ofmuscle action potential dueimpaired nerve-to-muscle transmission.
A different test called single fiber electromyography (EMG),which single muscle fibersstimulated by electrical impulses, can also detect impaired nerve-to-muscle transmission. EMG measureselectrical potentialmuscle cells. Muscle fibersmyasthenia gravis, as well as other neuromuscular disorders, do not respond as wellrepeated electrical stimulation comparedmuscles from normal individuals.
Computed tomography (CT) or magnetic resonance imaging (MRI) may be usedidentify an abnormal thymus gland orpresence ofthymoma.
A special examination called pulmonary function testing - which measures breathing strength - helpspredict whether respiration may faillead tomyasthenic crisis.
Treatment
Today, myasthenia gravis can be controlled. Thereseveral therapies availablehelp reduceimprove muscle weakness. Medications usedtreatdisorder include anticholinesterase agents such as neostigminepyridostigmine, which help improve neuromuscular transmissionincrease muscle strength. Immunosuppressive drugs such as prednisone, cyclosporine,azathioprine may also be used. These medications improve muscle strength by suppressingproductionabnormal antibodies. They must be usedcareful medical followup becausemay cause major side effects.
Thymectomy,surgical removal ofthymus gland (whichabnormalmyasthenia gravis patients), improves symptomsmore than 50 percentpatients without thymomamay cure some individuals, possibly by re-balancingimmune system. Other therapies usedtreat myasthenia gravis include plasmapheresis,procedurewhich abnormal antibodiesremoved fromblood,high-dose intravenous immune globulin, which temporarily modifiesimmune systemprovidesbodynormal antibodies from donated blood. These therapies may be usedhelp individuals during especially difficult periodsweakness. A neurologist, along withprimary care physician, will determine which treatment optionbesteach individual depending onseverity ofweakness, which musclesaffected, andindividual's ageother associated medical problems.
Myasthenic crises
A myasthenic crisis occurs when weakness affectsmuscles that control breathing, creatingmedical emergencyrequiringrespiratorassisted ventilation. In patients whose respiratory musclesweak, crises - which generally callimmediate medical attention - may be triggered by infection, fever, an adverse reactionmedication, or emotional stress.
Prognosis
With treatment,outlookmost patientsmyasthenia gravisbright:will have significant improvementtheir muscle weaknessthey can expectlead normal or nearly normal lives. Some casesmyasthenia gravis may go into remission temporarilymuscle weakness may disappear completely so that medications can be discontinued. Stable, long-lasting complete remissions aregoalthymectomy. Infew cases,severe weaknessmyasthenia gravis may causecrisis (respiratory failure), which requires immediate emergency medical care. (see above)
Ongoing research
WithinFederal Government,National InstituteNeurological DisordersStroke (NINDS), one ofFederal Government's National InstitutesHealth (NIH), has primary responsibilityconductingsupporting research on myasthenia gravis.
Much has been learned about myasthenia gravisrecent years. Technological advances have ledmore timelyaccurate diagnosis,newenhanced therapies have improved management ofdisorder. Much knowledge has been gained aboutstructurefunction ofneuromuscular junction,fundamental aspects ofthymus gland andautoimmunity, anddisorder itself. Despite these advances, however, therestill muchlearn. The ultimate goalmyasthenia gravis research isincrease scientific understanding ofdisorder. Researchersseekinglearn what causesautoimmune responsemyasthenia gravis, andbetter definerelationship betweenthymus glandmyasthenia gravis.
Today's myasthenia gravis research includesbroad spectrumstudies conductedsupported by NINDS. NINDS scientistsevaluating newimproving current treatments fordisorder. One such studytestingefficacyintravenous immune globlinpatientsmyasthenia gravis. The goal ofstudy isdetermine whether this treatment safely improves muscle strength. Another study seeksunderstandmolecular basissynaptic transmission innervous system. The objectivethis study isexpand current knowledge offunctionreceptors andapply this knowledge totreatmentmyasthenia gravis.
Source
''This articlebased onfactsheet byUS government:
