Monotherapy IVIG Gamunex-C for HMG-CoA Reductase Auto-Antibody Positive Necrotizing Myopathy Treatment (The MIGHT Trial)

Inclusion Criteria: A subject must meet all of the following inclusion criteria at screening to be eligible for participation in this study: * Anti-HMGCR positive. Patients will be screened by commercially-available ELISA. * Age ≥ 18 years * Demonstrable proximal muscle weakness: score of \<135 on the Proximal Manual Muscle Strength Testing 8-Muscle Group Assessment (MMT-8) (range 0-160). * Serum creatinine kinase (CK) more than 5 times the upper limit of normal * Muscle biopsy will not be required for eligibility in order to minimize the time to enrollment and initiation of treatment. Muscle biopsy will be obtained whenever possible as part of the standard of care. * Subjects must be willing and able to provide written informed consent. Exclusion Criteria: A subject meeting any of the following exclusion criteria at screening is NOT eligible for participation in this study: * Disease duration greater than 36 months. * Participants taking oral or intravenous glucocorticoids where the dose has changed within 4 weeks of screening. * Exposure to immunoglobulin treatment (IV, IM, or SubQ) in the prior 3 months * Exposure to plasma exchange (PEX) in the prior 3 months * Exposure to other immunosuppressive medications (e.g. methotrexate, leflunomide, azathioprine, mycophenolate mofetil) in the prior 6 months * Exposure to rituximab or any monoclonal antibody in the prior 12 months * Currently taking a statin medication * History of dermatomyositis rash (either biopsy-proven, o…