Plasma exchange for myasthenia gravis.

BACKGROUND: Myasthenia gravis is an autoimmune disease mediated by auto-antibodies direct against the nicotinic receptor for acetylcholine. Patients would be expected to benefit from plasma exchange. Non-randomised studies suggest that plasma exchange is beneficial in the short term.
OBJECTIVES: To examine the efficacy of plasma exchange in the short and long term treatment of myasthenia gravis. SEARCH STRATEGY: We searched the Cochrane Neuromuscular Disease Group register (searched 17 July 2002) and MEDLINE (January 1966 to June 2002) for randomised controlled trials using myasthenia gravis as the search term. We checked the bibliographies in reports of randomised trials and contacted one author to identify additional published or unpublished data. SELECTION CRITERIA: Types of studies: All randomised or quasi-randomised studies. TYPES OF PARTICIPANTS: All patients with myasthenia gravis who were diagnosed by an internationally accepted definition. Types of intervention: Treatment with plasma exchange alone or combined with steroids or immunosuppressive drugs. Types of outcome measures: PRIMARY OUTCOME MEASURE: ~bullet~patients treated for exacerbation: change in a specific muscle score after plasma exchange; ~bullet~patients treated for chronic myasthenia gravis: change in a functional scale. SECONDARY OUTCOME MEASURES: ~bullet~patients treated for exacerbation: change in a functional scale and percentage weaned from mechanical ventilation; ~bullet~patients treated for chronic myasthenia gravis: percentage in remission by the end of one year after first plasma exchange; ~bullet~adverse events. DATA COLLECTION AND ANALYSIS: One author extracted the data and the two others checked them. Since there was only one trial no formal meta-analysis was required. MAIN
RESULTS: We identified one randomised controlled trial. Improvement in a quantitative muscle score was not significantly greater in patients treated with plasma exchange and prednisone than in patients treated with prednisone alone one month after onset of treatment. More relapses were observed in the plasma exchange and prednisone group in the first year as compared with the prednisone alone group. Problems in recruitment and matching of patients entered into this trial limit the conclusions that can be drawn. On the other hand,experience from many non-randomised studies suggests that plasma exchange is beneficial in myasthenia gravis. Consequently the relative benefits of plasma exchange are still unconfirmed. REVIEWER'S
CONCLUSIONS: There are no adequate randomised controlled trials but many case series report short-term benefit from plasma exchange in myasthenia gravis, especially in myasthenic crisis. There are no adequate randomised controlled trials to determine whether plasma exchange improves the long-term outcome for myasthenia gravis. Further research is need to compare plasma exchange with alternative short-term treatments for myasthenic crisis and to determine the value of long-term plasma exchange for treating myasthenia gravis.