First-Line Intravenous Immune Globulin Monotherapy Evaluated in Idiopathic Inflammatory Myopathy

Dutch investigators conducted a Phase II open-label clinical study to evaluate the efficacy and safety of intravenous immune globulin (IVIG) as first-line treatment in a consecutive series of patients with newly diagnosed, biopsy-proved idiopathic inflammatory myopathy (IIM) of less than nine-month duration. Included were nine patients with dermatomyositis, six with immune-mediated necrotizing myopathy, four with nonspecific myositis/overlap myositis and one with anti-synthetase syndrome. Patients with inclusion-body myositis and prior use of immunosuppressants were excluded from the study. The treatment regimen consisted of IVIG (Privigen) monotherapy for a total of nine weeks, including a 2 g/kg body weight loading dose and two subsequent maintenance doses of 1 g/kg administered at three-week intervals. The primary outcome measure was the number of patients with at least moderate improvement on the 2016 ACR-EULAR Total Improvement Score.

Eight patients (8/19, 42 percent; Clopper-Pearson confidence interval 19.6, 64.6 percent) experienced at least moderate improvement by nine weeks. Of these responders, six patients demonstrated improvement by three weeks. Seven of the 19 evaluable patients required rescue medication due to insufficient efficacy and were prematurely withdrawn from the study. Three serious adverse events occurred, including a life-threatening pulmonary embolism in a study participant diagnosed with ovarian cancer during the study.

The investigators concluded first-line IVIG monotherapy led to clinically relevant improvement in nearly one-half of IIM patients, the majority of whom experienced a rapid clinical response. While advising caution about its use in patients with concomitant malignancy or other factors placing them at increased risk of thrombosis, the study authors recommended further studies to assess the efficacy of add-on IVIG treatment in combination with glucocorticoids.