ABSTRACT
The term idiopathic inflammatory myopathies (IIM) refers to a group of disorders of unknown cause in which immune-mediated inflammation results in muscle injury and complaints of weakness. IIM consist of six distinct subtypes including: type I- primary idiopathic polymyositis (PM), type II- primary idiopathic dermatomyositis (DM), type III- dermatomyositis or polymyositis associated with malignancy, type IV-juvenile dermatomyositis or polymyositis (JDM), type V- myositis associated with another connective tissue disease, and type VI- inclusion body myositis (IBM). 1 IIM is believed to be triggered by environmental factors in genetically susceptible individuals. Response to immunosuppressive therapies, frequent coexisting autoimmune diseases, existence of autoantibodies in patients’ serum, and experimental animal models all suggest an autoimmune pathogenesis. Patients develop proximal muscle weakness with or without tenderness of involved muscle. Laboratory tests reveal elevated serum muscle enzymes, myopathic changes by electromyography (EMG) and biopsy evidence of mononuclear cell infiltration with lymphocytes and plasma cells. Treatment includes corticosteroids, immunosuppressive drugs such as azathioprine, methotrexate, cyclophosphamide, cyclosporin and IVIG. While the overall prognosis for patients with IIM has improved in the last 20 years, there remain subsets of patients who continue to have active disease despite conventional therapy, for whom effects from long-term corticosteroids or immunosuppressive therapies are of concern, and for whom hematopoietic stem cell transplantation (HSCT) may be considered.
