A patient with muscle weakness

A 29 year old woman presented with symptoms of muscle weakness and difficulty swallowing. Physical examination showed swollen upper eyelids with a violaceous eruption (fig 1⇓). The dorsal side of her fingers was covered with an erythematous eruption. She also had bilateral symmetric purple discoloration of her skin in the area of the sternocleidomastoid muscle (fig 2⇓) and difficulty raising her arms above her head. A full blood cell count was normal. Creatinine kinase was raised at 1577 U/L (reference range 30-135).