Iago Pinal-Fernandez1,2, Maria Casal-Dominguez3,4, Andrew L Mammen5,6,7. 1. Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Expression, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, 50 South Drive, Room 1146, Building 50, MSC 8024, Bethesda, MD, 20892, USA. iago.pinalfernandez@nih.gov. 2. Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA. iago.pinalfernandez@nih.gov. 3. Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Expression, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, 50 South Drive, Room 1146, Building 50, MSC 8024, Bethesda, MD, 20892, USA. 4. Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA. 5. Muscle Disease Unit, Laboratory of Muscle Stem Cells and Gene Expression, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, 50 South Drive, Room 1146, Building 50, MSC 8024, Bethesda, MD, 20892, USA. andrew.mammen@nih.gov. 6. Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA. andrew.mammen@nih.gov. 7. Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA. andrew.mammen@nih.gov.
Abstract
PURPOSE OF REVIEW: Immune-mediated necrotizing myopathy (IMNM) is a type of autoimmune myopathy characterized by relatively severe proximal weakness, myofiber necrosis with minimal inflammatory cell infiltrate on muscle biopsy, and infrequent extra-muscular involvement. Here, we will review the characteristics of patients with IMNM. RECENT FINDINGS: Anti-signal recognition particle (SRP) and anti-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) autoantibodies are closely associated with IMNM and define unique subtypes of patients. Importantly, the new European Neuromuscular Centre criteria recognize anti-SRP myopathy, anti-HMGCR myopathy, and autoantibody-negative IMNM as three distinct subtypes of IMNM. Anti-SRP myopathy patients have more severe muscle involvement, have more common extra-muscular features, and may respond best to immunosuppressive regimens that include rituximab. In contrast, anti-HMGCR myopathy is often associated with statin exposure and intravenous immunoglobulin treatment may be an effective treatment, even as monotherapy. Both anti-SRP and anti-HMGCR myopathy tend to be most severe in younger patients. Furthermore, children with these forms of IMNM may present with dystrophy-like features which are potentially reversible with immunosuppressant treatment. IMNM patients with either autoantibody may experience fatty replacement of muscle soon after disease onset, suggesting that intense and early immunosuppressant therapy may provide the best chance to avoid long-term disability. IMNM is composed of anti-SRP myopathy, anti-HMGCR myopathy, and autoantibody-negative IMNM. Both anti-SRP and anti-HMGCR myopathy can cause severe weakness, especially in younger patients. Anti-SRP myopathy patients tend to have the most severe weakness and most prevalent extra-muscular features. Autoantibody-negative IMNM remains poorly described.
PURPOSE OF REVIEW: Immune-mediated necrotizing myopathy (IMNM) is a type of autoimmune myopathy characterized by relatively severe proximal weakness, myofiber necrosis with minimal inflammatory cell infiltrate on muscle biopsy, and infrequent extra-muscular involvement. Here, we will review the characteristics of patients with IMNM. RECENT FINDINGS: Anti-signal recognition particle (SRP) and anti-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) autoantibodies are closely associated with IMNM and define unique subtypes of patients. Importantly, the new European Neuromuscular Centre criteria recognize anti-SRP myopathy, anti-HMGCRmyopathy, and autoantibody-negative IMNM as three distinct subtypes of IMNM. Anti-SRP myopathypatients have more severe muscle involvement, have more common extra-muscular features, and may respond best to immunosuppressive regimens that include rituximab. In contrast, anti-HMGCRmyopathy is often associated with statin exposure and intravenous immunoglobulin treatment may be an effective treatment, even as monotherapy. Both anti-SRP and anti-HMGCRmyopathy tend to be most severe in younger patients. Furthermore, children with these forms of IMNM may present with dystrophy-like features which are potentially reversible with immunosuppressant treatment. IMNM patients with either autoantibody may experience fatty replacement of muscle soon after disease onset, suggesting that intense and early immunosuppressant therapy may provide the best chance to avoid long-term disability. IMNM is composed of anti-SRP myopathy, anti-HMGCRmyopathy, and autoantibody-negative IMNM. Both anti-SRP and anti-HMGCRmyopathy can cause severe weakness, especially in younger patients. Anti-SRP myopathypatients tend to have the most severe weakness and most prevalent extra-muscular features. Autoantibody-negative IMNM remains poorly described.
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