neurologic disorders
Myasthenia Gravis
Treatment of Myasthenia Gravis
Anticholinesterase drugs to relieve symptoms Corticosteroids, immunomodulating treatments (eg, IV immune globulin [IVIG], plasma exchange), immunosuppressants, or thymectomy to lessen the autoimmune reaction Supportive care In patients with congenital myasthenia, anticholinesterase drugs and immunomodulating treatments are not beneficial and should be avoided. Patients with respiratory failure require Tracheal Intubation and Anticholinesterase drugs are the mainstay of symptomatic treatment but do not alter the underlying disease process. Moreover, they rarely relieve all symptoms, and myasthenia may become refractory to these drugs. Pyridostigmineis begun at 60 mg orally every 3 to 4 hours and titrated up to a maximum of 120 mg/dose based on symptoms. When parenteral therapy is necessary (eg, because of dysphagia),neostigmine(1 mg=60 mg ofpyridostigmine) may be substituted. Anticholinesterase drugs can cause abdominal cramps and diarrhea, which are treated with oralatropine0.4 to 0.6 mg (given withpyridostigmineorneostigmine) orpropantheline15 mg 3 to 4 times a day. Patients who have been responding well to treatment and then deteriorate require respiratory support because they may have cholinergic crisis, and anticholinesterase drugs must be stopped for several days. Immunosuppressants (eg, corticosteroids,azathioprine,cyclosporine) interrupt the autoimmune reaction and slow the disease course, but they do not relieve symptoms rapidly. Thus, patients with myasthenic crisis require treatment with IVIG or plasma exchange. After being given IVIG 400 mg/kg once a day for 5 days, 70% of patients improve in 1 to 2 weeks. Effects may last 1 to 2 months. Plasma exchange (eg, 5 exchanges of 3 to 5 L plasma over 7 to 14 days) can have similar effects. Corticosteroids are necessary as maintenance therapy for many patients but have little immediate effect in myasthenic crisis. Over half of patients worsen acutely after starting high-dose corticosteroids. Initially,prednisone10 mg orally once a day is given; dose is increased by 10 mg weekly up to 60 mg, which is given for about 2 months, then tapered slowly. Improvement may take several months; then, the dose should be reduced to the minimum necessary to control symptoms. Azathioprine2.5 to 3.5 mg/kg orally once a day may be as effective as corticosteroids, although significant benefit may not occur for many months.Cyclosporine2 to 2.5 mg/kg orally twice a day may allow the corticosteroid dose to be reduced. These drugs require the usual precautions. Other drugs that may be beneficial includemethotrexate,cyclophosphamide, andmycophenolatemofetil. For patients with refractory disease, monoclonal antibodies (eg,rituximab,eculizumab) and the new modified monoclonal IgG1 Fc fragment efartigimod may be beneficial but are costly. Thymectomy may be indicated for patients with generalized myasthenia if they are < 80 years; it should be done in all patients with a thymoma. Subsequently, in 80%, remission occurs or the maintenance drug dose can be lowered. Plasma exchange or IVIG (the usual treatment for myasthenic crisis) may also be useful if patients are unresponsive to drugs before thymectomy. 