Cutaneous signs of classical dermatomyositis.

Idiopathic immune myopathies (IIM) are an heterogeneous group of autoimmune muscle disorders characterized by progressive muscle involvement. Dermatomyositis (DM) is the most common form of IIM. It is a multisystem disorder characterized by symmetric proximal, extensor, inflammatory myopathy, vascular involvement and a characteristic cutaneous eruption. Six types of DM have been identified: idiopathic, juvenile (JDM), cancer-related other autoimmune diseases-related, iatrogenic DM and amyopathic DM. Cutaneous manifestations of DM are the most important aspect of this disease and can precede from several months to years muscle or systemic involvement. Three groups of signs have been described: pathognomonic, highly characteristic and compatible. Although differences exist among the different clinical presentation of skin lesions, they share common histological findings including the presence of interface dermatitis with epidermal atrophy, basement membrane degeneration, vacuolar alteration of basal keratinocytes, and dermal changes consisting of interstitial mucin deposition and a sparse lymphocytic infiltrate. DM is a serious disease; the correct evaluation of any skin lesion suggesting an early diagnosis is of utmost importance. Skin signs may, also, represent a marker of treatment efficacy even though systemic symptoms worsening may not always be followed by more severe skin lesions.