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