Necrotising autoimmune myopathy – clinical aspects

Abstract

Necrotising autoimmune myopathy, (NAM), also sometimes referred to as immune-mediated necrotising myopathy, is an increasingly recognised condition. It can be caused by HMG CoA reductase inhibitors (statins), via the formation of anti-HMG CoA reductase antibodies, anti-SRP antibodies, viral infections and tumours. Clinically it is indistinguishable from polymyositis, being characterised by the subacute onset of symmetrical proximal limb weakness, elevated creatine kinase levels, and irritable myopathic findings on electromyography. Of interest, even at presentation it can be associated with significant muscle atrophy, which is a clinical clue to the underlying diagnosis. A muscle biopsy is essential for the diagnosis, and is distinguished from the other inflammatory myopathies by the absence of prominent inflammatory. Infiltrates and often negative MHC-I staining. This is an important condition to recognise and distinguish from other causes of myocyte necrosis, as it is amenable to immunotherapy, with combinations including prednisolone, methotrexate, azathioprine, mycophenolate, IVIG and rituximab. Necrotising autoimmune myopathy, (NAM), also sometimes referred to as immune-mediated necrotising myopathy, is an increasingly recognised condition. It can be caused by HMG CoA reductase inhibitors (statins), via the formation of anti-HMG CoA reductase antibodies, anti-SRP antibodies, viral infections and tumours. Clinically it is indistinguishable from polymyositis, being characterised by the subacute onset of symmetrical proximal limb weakness, elevated creatine kinase levels, and irritable myopathic findings on electromyography. Of interest, even at presentation it can be associated with significant muscle atrophy, which is a clinical clue to the underlying diagnosis. A muscle biopsy is essential for the diagnosis, and is distinguished from the other inflammatory myopathies by the absence of prominent inflammatory. Infiltrates and often negative MHC-I staining. This is an important condition to recognise and distinguish from other causes of myocyte necrosis, as it is amenable to immunotherapy, with combinations including prednisolone, methotrexate, azathioprine, mycophenolate, IVIG and rituximab.