A Cochrane review included 4 RCTs with 148 subjects with myasthenia gravis. In the first one on moderate or severe myasthenia gravis (MG, n=14) improvement after one month was not significantly greater for participants treated with plasma exchange and prednisone than for those treated with prednisone alone (95% CI -6.05 to 40.05). In the second one (n=12) comparing plasma exchange and iv. immunoglobulins (IVIg) with patients with moderate to severe MG, no significant difference was found in the efficacy of plasma exchange or IVIg after 4 weeks using a quantified myasthenia gravis score (QMGS). The third trial (n=87) with myasthenia gravis exacerbation found no significant difference between plasma exchange and IVIg after 2 weeks (95% CI: -5.72 to 7.72). However, very few patients with myasthenic crisis were included. The fourth study (n=35) showed a statistically significant difference in favour of plasma exchange before thymectomy in the duration of postoperative mechanical ventilation (1.3 vs. 1.7 hours, 95% CI - 2.12 to - 0.08) and the duration of ICU stay was 1.4 days vs. 1.9, 95% CI: - 2.30 to - 0.10).
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment), indirectness (very few patients with myasthenic crisis were included) and imprecise results (few patients and wide confidence intervals).