Myasthenia gravis is caused by antibodies in the blood which attack the junctions between nerves and muscles they stimulate. Plasma exchange removes these circulating auto-antibodies. Many case series suggest that plasma exchange helps to treat myasthenia gravis. Four randomised controlled trials were identified. In the first one, of 14 participants with moderate or severe myasthenia gravis, the myasthenic muscular score after one month was not significantly different for participants treated with plasma exchange and prednisone than for those treated with prednisone alone but there can be only low statistical confidence in the results of this study because of its small size. A randomised controlled cross-over trial of only 12 participants reported the same efficacy, after four weeks, of plasma exchange or intravenous immunoglobulins for the treatment of moderate to severe myasthenia gravis, but because of bias and a very weak statistical power the data prevent any conclusion. The third, including 87 participants, showed the same efficacy, after two weeks, of plasma exchange or intravenous immunoglobulins for the treatment of myasthenia gravis exacerbation. The fourth randomised controlled trial involving 35 participants reported a benefit from plasma exchange before thymectomy but this trial was heavily biased. No trial addressed the new subtype with antibodies to a muscle specific kinase. Further research is needed to determine the value of long-term plasma exchange for treating myasthenia gravis and to compare plasma exchange with alternative short-term treatments for myasthenic crisis or before thymectomy in both types of autoimmune myasthenia.
No adequate RCTs have been performed to determine whether plasma exchange improves the short- or long-term outcome for chronic myasthenia gravis or myasthenia gravis exacerbation. However, many studies with case series report short-term benefit from plasma exchange in myasthenia gravis, especially in myasthenic crisis. In severe exacerbations of myasthenia gravis one RCT did not show a significant difference between plasma exchange and intravenous immunoglobulin. Further research is need to compare plasma exchange with alternative short-term treatments for myasthenic crisis or before thymectomy and to determine the value of long-term plasma exchange for treating myasthenia gravis.
Myasthenia gravis is an autoimmune disease mediated by auto-antibodies most often directed against the nicotinic acetylcholine receptor. Less than five per cent of patients have auto-antibodies to a muscle tyrosine kinase. Patients would be expected to benefit from plasma exchange.
To examine the efficacy of plasma exchange in the short- and long-term treatment of myasthenia gravis.
We searched the Cochrane Neuromuscular Disease Group Specialized Register (31 January 2011), the Cochrane Central Register of Controlled Trials (CENTRAL) (31 January 2011, Issue 1 2011 in the Cochrane Library), MEDLINE (January 1966 to January 2011) and EMBASE (January 1980 to January 2011) using the term 'myasthenia gravis'. We checked the bibliographies of trial reports and contacted one author for additional data.
All randomised controlled trials (RCTs) or quasi-RCTs including all patients with generalised myasthenia gravis. We considered treatment trials of plasma exchange alone or combined with steroids or immunosuppressive drugs. The primary outcome measures were:(1) for exacerbation: change in a specific muscle score;(2) for chronic myasthenia gravis: change in a functional scale.
One author extracted and a second checked the data.
We identified four RCTs with 148 participants in total. In the first one, of 14 participants with moderate or severe myasthenia gravis, improvement after one month was not significantly greater for participants treated with plasma exchange and prednisone than for those treated with prednisone alone. A randomised controlled cross-over trial of 12 participants with moderate to severe myasthenia gravis found no statistically significant difference in the efficacy of plasma exchange or intravenous immunoglobulins after four weeks. A trial including 87 participants with myasthenia gravis exacerbation found no statistically significant difference between plasma exchange and immunoglobulin after two weeks. The fourth RCT, with 35 participants, showed a statistically significant difference in favour of plasma exchange before thymectomy. However these trials, except the third, are at high risk of bias and have a weak statistical power.