How do dermatomyositis and arthritis differ? how are they similar?

Different: Dermatomyositis is a condition that causes muscle and skin problems. Symptoms include rash, skin changes/discolorations, muscle weakness, fatigue, and muscle pain. Arthritis is a generic term that refers to joint inflammation. It does not usually affect muscle or skin, and typically causes joint pain, stiffness, and sometimes deformity. They are treated differently. A rheumatologist can help.