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Treatment: Myasthenia Gravis

  • The anticholinesterase drug pyridostigmine (Mestinon) titrated to assist pt with functional activities (chewing, swallowing, strength during exertion); usual initial dose of 30-60 mg 3-4 times daily; long-acting tablets help at night, but have variable absorption so are not reliable during the day (see Fig. 194-1). Muscarinic side effects (diarrhea, abdominal cramps, salivation, nausea) blocked with atropine/diphenoxylate or loperamide if required.
  • Plasmapheresis or IV immune globulin (IVIg; 400 mg/kg per day for 5 days) provides temporary boost for seriously ill pts; used to improve condition prior to surgery or during myasthenic crisis (see below).
  • Thymectomy improves likelihood of long-term remission in adult pts (~85% improve; of these, ~35% achieve drug-free remission); benefit is usually delayed by months to years; unclear if there is benefit in pts with pure ocular disease, children, or those age >55.
  • Glucocorticoids are a mainstay of chronic immunosuppressive treatment; begin prednisone at low dose (15-25 mg/d), increase by 5 mg/d every 2-3 days until marked clinical improvement or dose of 50-60 mg/d is reached. Maintain high dose for 1-3 months, then decrease to alternate-day regimen. Immunosuppressive drugs (mycophenolate mofetil, azathioprine, cyclosporine, tacrolimus, rituximab, and occasionally cyclophosphamide) may spare dose of prednisone required long-term to control symptoms.
  • Myasthenic crisis is defined as an exacerbation of weakness, usually with respiratory failure, sufficient to endanger life; expert management in an intensive care setting essential as is prompt treatment with IVIg or plasmapheresis to hasten recovery.
  • A number of drugs may exacerbate MG, potentially leading to crisis, and therefore should be avoided (Table 194-1).

For a more detailed discussion, see Drachman DB, Amato AA: Myasthenia Gravis and Other Diseases of the Neuromuscular Junction, Chap. 461, p. 2701, in HPIM-19.

Outline

Section 14. Neurology