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.
