Immune-Mediated Necrotizing Myopathy: Update on Diagnosis and Management

The idiopathic inflammatory myopathies (IIMs) comprise a group of autoimmune disorders that target skeletal muscle. They are characterized by typical laboratory and clinical features including muscle weakness, elevated muscle enzymes, characteristic histopathology of muscle biopsies, as well as electromyography abnormalities. The IIMs are divided into polymyositis, dermatomyositis, inclusion body myositis, nonspecific myositis, and immune-mediated necrotizing myopathy (IMNM). IMNM is distinguished by the absence of primary inflammation on muscle biopsy. IMNM may be associated with myositis-specific autoantibodies (i.e., anti-SRP and anti-HMGCR) and malignancy, in association with viral infections (HIV or hepatitis C), or in relation to other connective tissue diseases (i.e., scleroderma). Typical clinical findings such as severe muscle weakness, highly elevated creatine kinase (CK) levels, as well as resistance to conventional immunosuppressive therapy are associated with this subtype of IIM. This review provides an overview of this disease entity and focuses on its diagnosis and treatment.