Symptoms. The most common signs and symptoms of dermatomyositis include: 1  Skin changes. 2  A violet-colored or dusky red rash develops, most commonly on your face and eyelids and on areas around your nails, knuckles, elbows, knees, chest and back. The rash, which can be patchy with bluish-purple discolorations, is often the first sign of dermatomyositis. 2  Muscle weakness. 3  Progressive muscle weakness involves the muscles closest to the trunk, such as those in your hips, thighs, shoulders, upper arms and neck.