Diagnosis and management of idiopathic inflammatory myopathies
Oxford, United Kingdom
90 slide(s) – 00:42:34 – English – 2010-09-27
The idiopathic inflammatory myopathies are generally considered to include polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM). There is considerable evidence that PM and DM are autoimmune disorders - PM caused by a T-cell-mediated immune proces and DM by a humorally-mediated, complement dependent, microangiopathy. Despite their different immunopathologies the clinical features are similar and characterised by a proximal myopathy. The pathogenesis of IBM remains hotly debated.Whilst there are similar immunopathological features to PM, the lack of a significant clinical response to immunosuppressant drug treatments that are successful in PM and DM argues against autoimmunity having a primary role. The presence of protein aggregates, including amyloid, suggests a possible primary degenerative process, perhaps of the myonuclei. Clinically PMand DMpresent as progressive proximal myopathies - PMbeing slowly progressive and DM sub-acutely or, rarely, acutely presenting. Rash is a very common, but not invariable, feature of DM. Serum creatine kinase is usually elevated, EMG shows characteristic features, and muscle biopsy remains the gold standard of diagnosis. Dermatomyositis in adults, but not children, may be paraneoplastic and occult malignancy must be sought. Immunosuppressant drug therapy is usually successful. In IBMthe highly characteristic, and almost diagnostic, pattern of muscle involvement is with early involvement of the long finger flexors and quadriceps. Asymmetry is common. Dysphagia can be very disabling and is rarely a presenting feature. Characteristic biopsy findings include rimmed vacuoles and protein aggregations. Response to immunosuppression is poor and many specialists do not recommend it. Recently it has been suggested that the long-established Griggs diagnostic criteria should be revised.