Dermatomyositis is a multisystem autoimmune connective tissue disease that is most often characterized by a symmetric proximal extensor inflammatory myopathy, a characteristic violaceous cutaneous eruption, and pathogenic circulating autoantibodies. Dermatomyositis demonstrates a bimodal incidence, with the adult form most commonly seen in individuals aged 45-60 and the juvenile form found in children aged 10-15 years. A 2:1 female-to-male incidence ratio exists in adults.

The distinctive nail findings of dermatomyositis help distinguish it from other connective tissue disorders. Thickened, hyperkeratotic, ragged cuticles and telangiectasias of the proximal nail fold (PNF) are the characteristic nail findings. Some other rare nail findings have been reported, including complete loss of several toenails, red lunulae, and ventral pterygium. The presence of ischemic lesions might be predictive of malignancy in dermatomyositis of adulthood.

In addition to the nail findings, other cutaneous findings such as periorbital heliotrope rash, atrophic dermal papules of dermatomyositis (ADPDM, formerly called Gottron papules) (slightly atrophic, flat-topped papules over the proximal interphalangeal joints), and poikiloderma should also be present. ADPDM may involve the vicinity of the PNF. Other characteristic features may include flat erythema of the upper back and posterior neck and shoulders (shawl sign) as well as a similarly presenting macular erythema of the anterior neck and upper chest (V sign) that can worsen with ultraviolet exposure. Patients may also have poikiloderma over the lateral hip (holster sign). Muscle involvement affects proximal muscle groups in a symmetric fashion.

Dermatomyositis may be induced by medications, including hydroxyurea, penicillamine, interferon beta, and ipilimumab. Acute onset / flares of dermatomyositis have been reported in association with ingestion of IsaLean, an herbal supplement.