DEFINITION:Myastheniagravis (abbreviatedas MG) is anautoimmune neuromusculardisease leading tofluctuating muscleweakness and fatigibility.It is a typeof autoimmunedisorders.
CLASSIFICATION:•Class I: Any eye muscle weakness, possible ptosis, no other evidence ofmuscle weakness elsewhere•Class II: Eye muscle weakness of any severity, mild weakness of othermuscles 1)Class II a: Predominantly limb or axial muscles 2)Class II b: Predominantly bulbar and/or respiratory muscles•Class III: Eye muscle weakness of any severity, moderate weakness ofother muscles 1)Class III a: Predominantly limb or axial muscles 2)Class III b: Predominantly bulbar and/or respiratory muscles•Class IV: Eye muscle weakness of any severity, severe weakness of othermuscles 1)Class IV a: Predominantly limb or axial muscles 2)Class IV b: Predominantly bulbar and/or respiratory muscles (Can also include feeding tube without intubation)•Class V: Intubation needed to maintain airway.
SYMPTOMS:The first noticeable symptom isweakness of the eyemuscles, difficulty in swallowingand slurred speech may also be thefirst signs.Muscles that control eye andeyelid movement, facialexpressions, chewing, talkingand swallowing becomesweaker.The muscles thatcontrol breathing and neck andlimb movements can also beaffected.
CAUSES OFMYASTHENIA GRAVIS:It occurs when normalcommunication between thenerve and muscle isinterrupted at theneuromuscular junction.Normally when impulsestravel down the nerve, thenerve endings release aneurotransmitter substancecalled acetylcholine whichtravels from theneuromuscular junction andbinds to acetylcholinereceptors which are activatedand generate a musclecontraction.
Causes:In MG, the auto antibodiesmost commonly actagainst the nicotinicacetylcholinereceptor (nAChR),the receptor in the motorend plate for theneurotransmitter acetylcholine that stimulatesmuscular contractions.Some forms of theantibody impair the abilityof acetylcholine to bind toreceptors thus preventingmuscle contraction.
ROLE OF THYMUS:The antibodies are producedby plasma cells, derived fromB-cells. B-cells convert intoplasma cells by T-helper cellstimulation. To carry out thisactivation, T-helpers mustfirst be activatedthemselves, which is done bybinding of the T-cellreceptor (TCR) to theacetylcholine receptorantigenic peptide fragment(epitope). Since the thymusplays an important role in thedevelopment of T-cells, so itis closely related withmyasthenia gravis.
DURING PREGNANCY: Up to 10% of infants with parents affected by the condition are born with transient (periodic) neonatal myasthenia (TNM), which generally produces feeding and respiratory difficulties. TNM usually presents as poor suckling and generalized hypotonia (low muscle tone). Immuno suppressive therapy should be maintained throughout pregnancy, as this reduces the chance of neonatal muscle weakness, as well as controls the mothers myasthenia.
DIAGNOSIS:• Physical examination(eyes, feet, arms)• Blood tests(for antibodies against acetylcholine receptors)• Electrodignostics(measure fatiguability of the muscle)• Ice test• Edrophonium test(intravenous administration of edrophonium chloride to increase acetylcholine)• Imaging(x-ray of thymus)• Pulmonary function test(lung function testing)• Pathological findings(Muscle biopsy)
MANAGEMENT:• Plasmapheresis can be used to remove the putative antibodies from the circulation. Plasmapheresis is a blood purification procedure used to treat several autoimmune diseases.• Surgery:Thymectomy, the surgical removal of the thymus, is essential in cases of thymoma.• Physical activity:Exercise participation