Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Dermatomyositis ?
    ### Response:
    Dermatomyositis is one of a group of muscle diseases known as the inflammatory myopathies, which are characterized by chronic muscle inflammation accompanied by muscle weakness. Dermatomyositis cardinal symptom is a skin rash that precedes, accompanies, or follows progressive muscle weakness.
    