muscleDiseaseAndAnesthesia

muscleDiseaseAndAnesthesia - Neuromuscular Disorders:...

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Neuromuscular Disorders: disorders of neuromuscular junction, motor neuron, and muscle Kasia Petelenz Greg Gordon (and others) November 15, 2005
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Myasthenia Gravis Incidence 1:10,000 to 1:30,000 Women 20 – 30 years of age are most often affected; men older than 60 display symptoms Acquired chronic autoimmune disorder Hallmarks are weakness and rapid exhaustion of voluntary skeletal muscles
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Myasthenia Gravis Muscle strength characteristically improves with rest, deteriorates rapidly with exertion Skeletal muscle atrophy is unlikely Laryngeal and pharyngeal muscle weakness may lead to aspiration, problems clearing secretions, difficulty chewing.
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Myasthenia Gravis Presentations Clinical Classification Class 1: ocular symptoms only Class 1A: ocular symptoms with EMG evidence of peripheral muscle involvement Class 2A: mild generalized symptoms Class 2B: more severe and rapidly progressive symptoms Class 3: acute and presenting in weeks to months with severe bulbar symptoms Class 4: late in the course of disease with severe bulbar symptoms and marked generalized weakness
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Myasthenia Gravis Disease course marked by exacerbations and remissions Infection, stress, surgery, pregnancy have unpredictable effects, but often cause exacerbations Antibiotics can aggravate weakness Diseases considered AI in origin often coexist Decreased thyroid function RA SLE Pernicious Anemia
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Mechanism - MG Decrease in functional Acetylcholine receptors at the nicotinic neuromuscular junction 70% - 90% have circulating antibodies to AChR’s Neonatal Transient born to mothers with MG – Ab’s cross placenta Only 12% symptomatic
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Therapy - Myasthenia Gravis Immunosuppressants: Steroids - Commonly cause dose dependent weakness Azathioprine,Cyclosporine Plasmapheresis, iv immunoglobulin Acute exacerbations, i.e. in immediate post-operative period if anticholinesterases have been withheld and symptoms are severe Plasmapheresis + IVIG for 5 days -> rapid improvement, may last for weeks Thymectomy
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Important part of Rx Anticholinesterase drugs Pyridostigmine, po duration of 2-4 hours Excessive administration -> Cholinergic Crisis SLUDGE: Salivation, lacrimation, urination, defecation, + miosis + bradycardia + bronchospasm Profound weakness: due to excess Ach at NMJ -> persistent depolarization Treatment of Cholinergic Crisis: Atropine, Mechanical Ventilation if needed
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Anesthetic Concerns - MG Pre-op Predictors of Need for Post-Operative Ventilatory Support Disease duration > 6 years Concomitant pulmonary disease Maximum inspiratory force (MIF) <-25cm H2O VC < 4 mL/kg Pyridostigmine dose >750 mg/day
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Anesthetic Considerations Old School : Recommended to d/c anticholinesterase if pt has only mild weakness Theory: Potentiates Sux, inhibit effect of NDMR’s Pts more susceptible to vagal arrhythmias
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muscleDiseaseAndAnesthesia - Neuromuscular Disorders:...

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