Polymyositis and dermatomyositis - challenges in diagnosis and management

Abstract

Polymyositis (PM) and dermatomyositis (DM) are different disease subtypes of idiopathic inflammatory myopathies (IIMs). The main clinical features of PM and DM include progressive symmetric, predominantly proximal muscle weakness. Laboratory findings include elevated creatine kinase (CK), autoantibodies in serum, and inflammatory infiltrates in muscle biopsy. Dermatomyositis can also involve a characteristic skin rash. Both polymyositis and dermatomyositis can present with extramuscular involvement. The causative factor is agnogenic activation of immune system, leading to immunologic attacks on muscle fibers and endomysial capillaries. The treatment of choice is immunosuppression. PM and DM can be distinguished from other IIMs and myopathies by thorough history, physical examinations and laboratory evaluation and adherence to specific and up-to-date diagnosis criteria and classification standards. Treatment is based on correct diagnosis of these conditions.

Keywords: APC, antigen presenting cell; AZA, Azathioprine; CAM, cancer associated myositis; CK, creatine kinase; DM, dermatomyositis; Dermatomyositis; Diagnosis criteria; EMG, electromyography; HLA, human leukocyte antigen; IIM, idiopathic inflammatory myopathies; ILD, interstitial lung disease; IV, intravenous; Idiopathic inflammatory myopathy; JDM, juvenile dermatomyositis; MAA, myositis associated antibody; MAC, membrane attack complex; MHC, major histocompatibility complex; MMF, mycophenolate mofetil; MRI, magnetic resonance imaging; MSA, myositis specific antibody; MTX, methotrexate; MUAP, motor unit action potential; NAM, necrotizing autoimmune myopathy; PM, polymyositis; Polymyositis; TNF, tumor necrosis factor; Treatment; Treg, regulatory T cell; UVR, ultraviolet radiation; sIBM, sporadic inclusion body myositis.