Myasthenia Gravis

Myasthenia Gravis Osserman and Genkins classification: • Class I—ocular symptoms only • Class IA—ocular S’s with EMG evidence of peripheral muscle involvement • Class IIA—mild generalized symptoms • Class IIB—more severe and rapidly progressive symptoms • Class III—acute, presenting in weeks to months with severe bulbar symptoms • Class IV—late in the course of the disease with severe bulbar symptoms and marked generalized weakness • autoimmune disease with anti-acetylcholine receptor antibodies, F>M • Abnormal thymus glands 75% of pts(85% show hyperplasia; 15% thymoma). 75% of pts either go into remission or are improved post-op • Medical ttt: anticholinesterase, steroids, other immunosuppressant (azathioprine, cyclophosphamide, cyclosporine)and plasmapheresis. • underdosage → “myasthenic crisis” whereas overdosage will produce a “cholinergic crisis.” Excessive doses of cholinesterase inhibitors produce abdominal cramping, vomiting, diarrhea, salivation, bradycardia, and skeletal muscle weakness that mimics the weakness of myasthenia , to differentiate

between them→”Tensilon test” 2-10 mg IV Edrophonium→ with M.crisis they improve, but not with C.crisis. • Sensitive to NDMR, resistant to Sux→ ↑ dose to 1.5 mg/kg Anesthesia Management • best to be done 1st case during the day, avoid pre-med • Best to hold the AM dose of anticholinesterase, unless the Pt is physically and/or psych dep A→ possible mediastinal mass, may need RSI, possible Difficult with other diseases B→ frequent aspiration, resp failure → PFT C→ focal myocarditis, A.fib , AV block D→ steroids (stress dose), immunosuppressant, anticholinesterase(dose), avoid drugs that may potentiate NMB (aminoglycoside ABx, quinidine, CCB) H→ anemia, ITP, lymphoma, leukemia CNS→ MS M→ thyroid dysfunction ↑ or ↓, Other→ R. arthritis, SLE, scleroderma Lab→ CBC, lytes (abnormality may ↑ weakness), PFT, ECG, chest CT, CXR. • Monitor N. stimulator.

• Post-op problems : pneumonia due to poor coughing, Aspiration, resp failure Leventhal, assigned a scoring system to four factors they found to be predictive for requirement of post-op mechanical vent (for transternal thymectomy) • Duration of >6 years 12 points • History of chronic obstructive pulmonary disease 10 points • >750 mg/d pyridostigmine 8 points • Vital capacity <2.9 liters 4 points Patients scoring <10 points in their series could be extubated immediately postoperatively; those scoring >12 points required postoperative ventilatory support. • Post-op pain Mx best using regional anesthesia • Have an ICU backup bed ready. • Extubation criteria o Awake and responsive, stable V/S, good grip, sustained head left o Good ABG, on FiO2 < 40%(>90%sat) , with adequate vent and oxy maintained by the Pt o –ve inspiratory pressure > -20cmH2O o VC > 15ml/kg • Pregnancy may cause exacerbation or remission, with ↑ remission postpartum

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The neonate may have transient MG