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Toronto Notes 2019 Neuromuscular Junction Diseases
Treatment
• firstlinetreatment:acetylcholinesteraseinhibitors(e.g.pyridostigmine)
• corticosteroids:mainstayoftreatmentifacetylcholinesteraseinhibitorsdonotresultindiseasecontrol
(e.g. prednisone)
• immunosuppression: can be used as steroid-sparing therapy (e.g. azathioprine, cyclophosphamide,
mycophenolate)
• short-termimmunomodulation:Forcrisis(e.g.IVIGandplasmapheresis)
• thymectomy:optioninnon-thymomatousMG;85%remissionrate
Prognosis
• 30%eventualspontaneousremission
• withtreatment,lifeexpectancyisequaltothatofapersonwithoutMG,butqualityoflifemayvary
Lambert-Eaton Myasthenic Syndrome
Etiology and Pathophysiology
• autoimmunedisorderduetoantibodiesagainstpresynapticvoltage-gatedcalciumchannels,causing decreased ACh release at the NMJ
• 50-66%areassociatedwithsmallcellcarcinomaofthelung
Clinical Features
• weaknessofskeletalmuscleswithoutsensoryorcoordinationabnormalities,proximalandlower muscles more affected
• reflexesarediminishedorabsent,butincreaseafteractivemusclecontraction
• bulbarandocularmusclesaffectedin25%(vs.90%inMG)
• prominentanticholinergicautonomicsymptoms(drymouth>impotence>constipation>blurred
vision)
Investigations
• edrophoniumtest→noresponse • EMG
■ rapid (>10 Hz) repetitive stimulation → incremental response
■ post-exercise facilitation → incremental response with exercise • screenformalignancy,especiallysmallcelllungcancer
Treatment
• tumourremoval • AChmodulation
■ increased ACh release (3,4-diaminopyridine)
■ decreased ACh degradation (pyridostigmine)
• immunomodulation-steroids,plasmapheresis,IVIG
Botulism
Etiology and Pathophysiology
• causedbyatoxinproducedbysporesofClostridiumbotulinumbacteria,whichcanenterthrough wounds or by ingestion
• infantilebotulismisthemostcommonformandisusuallyfromingestionofhoneyorcornsyrup
Clinical Features
• occur6-48hafteringestion
• CNparalysis:ptosis,extraocularmuscleweakness,dilatedpoorlyreactivepupils,dysarthria,jaw
weakness, dysphagia
• autonomicdysfunction:nausea,orthostatichypotension,constipation(paralyticileus),bladder
distension
• anticholinergicsymptoms:drymouth,constipation,urinaryretention
• spreadstotrunkandlimbs:symmetricweaknesswithparalysisandabsent/decreaseddeeptendon
reflexes
• patternofparesisoftenstartswithGIsymptoms,→extraocularmuscleweakness,→dysphagia,→
limbs, and respiratory involvement; all associated with dry mouth
• rarelyrespiratorydistress,potentiallyadvancingtorespiratoryfailure
Investigations
• bloodtestfortoxin,stoolculture
• CT/MRItoruleoutstroke,lesion(normalinbotulism)
Treatment
• botulinumanti-toxin–goodprognosiswithprompttreatment • supportivetherapyasrequired
Neurology N39
®
Tensilon isadrugthatinhibits
acetylcholinesterase. It improves muscle function immediately in myasthenia gravis, but not in a cholinergic crisis
This test is infrequently used; when performed, a crash cart should be nearby as respiratory difficulty and/or bradycardia may occur
Anti-Ca channel antibodies
Ca2+
Ca2+ channel
ACh
No ACh release
NO CONTRACTION
© Minyan Wang 2012
Figure 25. Lambert-Eaton myasthenic syndrome (LEMS)