Outcome measures in the idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies (IIM) are a heterogeneous group of rare autoimmune disorders that share some similarities, such as proximal predominant symmetric muscle weakness, also known as myopathy pattern 1,1 except for myopathy pattern 4 (distal arm and proximal leg weakness), in inclusion body myositis (IBM).1,2 Common features in IBM, dermatomyositis, polymyositis, and necrotizing autoimmune myopathy, frequently include serum creatine kinase (CK) elevation and myopathy with muscle membrane irritability on EMG. Muscle histopathology findings vary depending on the underlying disease, and may include inflammatory exudates of variable distribution, intact myofiber lymphocytic invasion, widespread necrosis and phagocytosis, or, in the case of IBM, rimmed vacuoles and protein aggregation.2,3