Dermatomyositis and polymyositis are inflammatory myopathies with muscle inflammation and proximal muscle weakness. Skin examination, muscle enzyme measurement (creatinine kinase, aldolase) assessment of antinuclear and myositis-specific antibodies (MSA), muscle or skin biopsy, electromyography (EMG), magnetic resonance imaging (MRI) of skeletal muscle and exclusion of malignancy are very important. Histologic signs of DM and PM include degeneration, regeneration, inflammatory cell infiltration and ultimately, muscle fiber necrosis. In DM, the cellular infiltrate is perifascicular and perivascular with infiltration of B lymphocytes and plasmacytoid dendritic cells. In PM, the cellular infiltrate in muscle is in the fascicle, with cytotoxic CD8+ T cells. Skin changes characteristic of DM are Gottron’s papules, a heliotrope rash and V sign. EMG findings include spontaneous fibrillations, positive sharp waves, and complex repetitive discharges. DM is diagnosed in patients with symmetrical proximal muscle weakness, increased muscle enzymes and a specific rash. Biopsy is not required. EMG and muscle biopsy may be useful in patients who have atypical findings to exclude other diseases such as inclusion body myositis (IBM), metabolic myopathy, or muscle dystrophies. Exclusion of other diseases such as inflammatory myopathies, motor neuron disease, myasthenia gravis, muscular dystrophies, inherited, metabolic, drug-induced, endocrine, and infectious myopathies must be performed. Muscle strength and CK levels monitor disease activity. GCS are the main lines of treatment used. Combined therapy includes methotrexate, azathioprine and antimalarial drugs. Cyclophospamide and intravenous gamma-globulin have a role in life-threatening cases. Plasmapheresis is used only when the above mentioned therapies have failed.
Keywords: Aldolase, ANA, Creatinine kinase, Dermatomyositis, Drug-induced, Electromyography (EMG), Endocrine myopathies, Idiopathic inflammatory myopathies, Inherited, Malignancy, Metabolic, Motor neuron disease, MRI, Muscle biopsy, Muscle enzyme, Muscle fiber necrosis, Muscle weakness, Muscular dystrophies, Myasthenia gravis, Myositis-specific antibodies (MSA), Polymyositis, Skin biopsy.