Excessive dosage of neostigmine or pyridostigmine causes weakness that cannot be differentiated clinically from myasthenia. The disease may become refractory to the drug. Thus, if a patient who has been doing well deteriorates, the cause must be determined with the IV edrophonium test. If the patient improves, the maintenance dosage is inadequate. If the patient worsens, dosage is excessive or the disease is refractory.
Corticosteroids are useful for long-term treatment and are less useful for crisis.
Alternate-day dosage of prednisone 60 to 70 mg usually induces improvement in a few months, after which the dose should be reduced to the minimum necessary. These drugs should be given with the usual precautions. A thymoma, if present, should be excised to prevent spread within the mediastinum. Plasmapheresis may be useful before thymectomy in refractory patients and during crisis. All rights reserved.