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Acquired myasthenia gravis (MG) is an autoimmune disorder treated with cholinesterase inhibitors and a number of immunotherapies. Intravenous immunoglobulin (IVIG) is an expensive and commonly used immunotherapy for patients with an exacerbation of MG, but its effectiveness has only recently been demonstrated in a randomized clinical trial. This paper describes the study design, results, and limitations of a double-blind, randomized, placebo-controlled trial designed to definitively determine if IVIG benefits patients with MG who present with worsening weakness. Fifty-one patients with worsening weakness due to MG were randomized to receive either 2 g/kg of IVIG over 2 days or an equivalent volume of placebo (5% dextrose in water). The Quantitative MG Score (QMG Score) for Disease Severity, a validated clinical composite scale and the primary outcome measure in the study, was calculated by a masked observer 14 and 28 days after treatment. Patients treated with IVIG demonstrated a significant improvement in QMG Score for Disease Severity at day 14 and the response persisted at day 28. The largest clinical improvement occurred in patients with more severe disease. IVIG was well tolerated with no significant side effects observed. Given the observed efficacy and safety of IVIG demonstrated in this trial, future studies are necessary to determine if there is a role for interval IVIG treatments in chronic MG. [ABSTRACT FROM AUTHOR]