Medical therapies in myasthenia gravis.

Forty years ago, a patient with MG probably had a fifty-fifty chance of surviving a myasthenic crisis, defined as the need for mechanical ventilatory support. Approximately 16% of all patients experience a crisis, a figure that has not changed appreciably since then. Progressive weakness, oropharyngeal symptoms, refractoriness to anticholinesterase medication, intercurrent infection, and invasive procedures including needle biopsies of thymic gland masses, and reactions to contrast agents used in the performance of CT of the chest have been implicated in the development of crisis. It is now standard practice to treat severe crisis in an intensive care unit. The ready availability of intensive care in most hospitals belies the fall in the mortality of myasthenic crisis to 6% over the past several decades. Crisis is a temporary exacerbation, regardless of the proximate cause, and the goal is to keep the patient alive until it subsides, usually in 2 weeks. In the past, edrophonium was used to differentiate myasthenic crisis from cholinergic crisis, but that is now moot because withdrawal of cholinesterase medication is necessary for improvement in both situations. The underlying immunologic derangements in myasthenic crisis are not well understood, but there is a rapidly fatal antibody-mediated syndrome that bears resemblance to crisis and is associated with inflammation and necrosis of the end-plate region.