Clinical and histological features of immune-mediated necrotising myopathy: A multi-centre South Australian cohort study

• Published in: Neuromuscular disorders : NMD 2020-03, Vol.30 (3), p.186-199
• Main Authors: Day, Jessica, Otto, Sophia, Cash, Kathy, Limaye, Vidya
• Format: Article
• Language: English
• Subjects: Aged; Autoantibodies - blood; Autoimmune Diseases - ethnology; Autoimmune Diseases - immunology; Autoimmune Diseases - pathology; Autoimmune Diseases - physiopathology; Female; Follow-Up Studies; Humans; Idiopathic Inflammatory Myopathy; Immune-mediated necrotising myopathy; Immune-mediated necrotizing myopathy; Immunotherapy; Indigenous health; Male; Middle Aged; Myositis; Myositis - ethnology; Myositis - immunology; Myositis - pathology; Myositis - physiopathology; Necrosis - ethnology; Necrosis - immunology; Necrosis - pathology; Necrosis - physiopathology; Necrotizing autoimmune myopathy; Phenotype; Registries; Retrospective Studies; Severity of Illness Index; South Australia - ethnology
• ISSN: 0960-8966; 1873-2364; 1873-2364
• DOI: 10.1016/j.nmd.2020.02.003

•Immune-mediated necrotising myopathy is clinically and histologically heterogeneous.•Many patients present with severe weakness and few recover full power by one year.•Complement deposition on myofibres closely correlates with clinical severity.•Aboriginal and Torres Strait islander patients present with a severe phenotype. Immune-mediated necrotising myopathy (IMNM) is a recently described entity. We describe a cohort of South Australian IMNM patients in order to define the spectrum of disease, characterise features that distinguish IMNM from other idiopathic inflammatory myopathy (IIM) subtypes and identify factors associated with clinically severe disease. Subjects were identified from the South Australian Myositis Database (SAMD), a histologically defined registry. Consecutive muscle sections from patients with IMNM (n = 62), other forms of IIM (n = 60) and histologically normal muscle (n = 17) were stained using immunohistochemistry and graded. Clinical information was collected from the SAMD and through retrospective chart review. IMNM patients displayed clinical and histological heterogeneity. While most (67%) were profoundly weak at presentation, 24% exhibited mild to moderate weakness and 9% had normal power. Histological myonecrosis ranged from minor to florid. The amount of myofibre complement deposition was closely associated with clinical severity. Patients of Aboriginal and Torres Strait Islander heritage and those with anti-SRP autoantibodies present with a severe phenotype. Despite intense immunotherapy, few IMNM patients recovered full power at one year follow up. The identification of clinical, serological and histological features which are associated with severe forms of the disease may have diagnostic and therapeutic utility.