National Board Ex- 6 Book .pmd - National Board Of Examination

11ReviewArticleMyasthenia Gravis and Anaesthetic ImplicationsRavinder Kumar Batra, Kajari RoyDepartment of Anaesthesiology, All India Institute of Medical Sciences, New DelhiMyasthenia gravis is anautoimmune disease,with an incidence of0.25 to 2.0 per 100,000 people,resulting from the production ofantibodies against the alphasubunit of nicotinic acetylcholinereceptors of the endplate 1, 2, 3, 4 .These antibodies reduce thenumber of active receptors,brought about either byfunctional block of the receptors,by increased rate of receptordegradation, or by complementmediatedlysis. Repetitive nervestimulation results in adecremental response. Thedisease is frequently associatedwith morphologic alabnormalitiesof the thymus 5 . In youngpatients, thymic hyperplasia iscommon while thymoma is morefrequent in elderly patients.Myasthenia gravis may beassociated with other disordersof autoimmune origin suchas thyroid hypofunction,rheumatoid arthritis, andsystemic lupus erythematosus.Clinical presentationsl Transient neonatal myasthenia- It is present in 20% ofneonates born to myasthenicmothers, with difficulty insucking and swallowing, difficultywith breathing, ptosisand facial weakness. The conditionhas a tendency to spontaneousremission, usuallywithin two to four weeks.l Congenital or infantilemyasthenia-These childrenhave variable muscleweakness from birth dueto congenital endplateacetylcholine-receptordeficiency.The condition isnot autoimmune in nature,and hence therapy primarilydepends on anticholinesterasetherapy.l Juvenile myasthenia-This issimilar in pathogenesis andtreatment to the adult variety,except that thymoma is not afeature in these cases.l Adult Myasthenia Gravis(MG)-The incidence is about1 in every 20,000 adults.There is a preponderance ofwomen, Hyperplasia of thethymus gland is present inover 70% of patients, and 10-15% have thymomas. Theclinical course of MG ismarked by periods ofexacerbations and remissions.History & Clinical examination- The extraocular musclesare involved at some time in thecourse of the disease in almostevery patient during the first year.Weakness of pharyngeal and laryngealmuscles (bulbar muscles)results in dysphagia and dysarthria.Arm, leg, or truncal weaknesscan occur in any combinationand is usually asymmetricalin distribution. After the diseasereaches its maximum severity,most patients who survive continuewith a chronic form of thedisease with fewer and less severeepisodes of exacerbation.A detailedcentral nervous system examinationshould be performed.This will show normal highermental functions and unalteredsensory system function. A motorsystem examination enablesthe anaesthesiologist to gauge theseverity of the disease process,and this shows involvement ofthe lower cranial nerves and anasymmetrical muscle involvementin the rest of the body.Classification Of MyastheniaGravis(Ossermann andGenkins)I Ocular signs and symptomsonlyII A Generalized mildmuscle weaknessIIB Generalized moderateweakness, and/or bulbardysfunctionIII Acute fulminating presentation,and/or respiratorydysfunctionIV Late severe generalizedmyasthenia gravisThe distribution, severity, andoutcome of the disease aredetermined during the first oneto three years after the onset. In14%, the disease remainsclinically localized to extraocularmuscles and in the remaining86%, becomes generalized.Journal of Postgraduate Medical Education, Training & Research69