Dermatomyositis (DM) is an inflammatory muscle disease of unknown etiology. Immune disorders are involved to various degrees (depending on the type of inflammatory myopathy) in the physiopathogenesis of the disease, as documented by clinical, biological and experimental findings. DM occurs at all ages, with, however, two small peaks in frequency: between the ages of 5 and 14 years, when DM is almost exclusively observed, and after 40 years. It is an acquired disorder, even though there may be a predisposing genetic background. Onset is often acute but may be progressive. Clinically, DM is defined by characteristic skin symptoms (photosensitive erythroedema on exposed areas), muscle weakness, inflammation of the pharyngeal muscles causing deglutition disorders and requiring emergency hospitalization in specialized units. Other signs, such as arthralgias and palpitations, are less common. Arguments supporting the diagnosis include: clinical findings, serum muscle enzymes (creatine phosphokinase (CPK) and aldolases) are often but not always elevated, the electromyogram tracings and, most importantly, muscle biopsy results showing myolysis of ischemic origin, necrosis, regeneration, perivascular B and CD4 inflammatory infiltrates and endothelial membrane attack complex deposits, which alone can confirm the diagnosis. DM may be associated with other affections, especially autoimmune diseases, malignancies (essentially breast, uterine or ovarian cancer in women, whereas bronchial epithelium, prostate or digestive tract tumors in men) pathologies, and indeed they should systematically be sought when DM is suspected. Therapeutic management includes immunomodulating treatments and physical therapy, once the acute inflammatory phase is over. DM is a rare connective tissue disease, with estimated incidence of 5-10 cases/million inhabitants/year and prevalence of 6-7 cases/100,000 people. Corticotherapy is the first-choice treatment, since it is effective on a long-term basis in 60-70% of the patients. In cases of corticosteroid intolerance or dependence, or primary or secondary corticoresistance, several immunosuppressants can be prescribed, with variable efficacy. Many new treatments have recently been used for patients with DM refractory to classical treatments, in particular cyclosporin A and intravenous human polyvalent immunoglobulins. Several clinical, fundamental and therapeutic protocols applied to inflammatory myopathies are currently being assessed.
Last update: March 2003