Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Psoriatic Arthritis ?
    ### Response:
    Psoriasis is a skin disease that causes itchy or sore patches of thick, red skin with silvery scales. You usually get them on your elbows, knees, scalp, back, face, palms and feet, but they can show up on other parts of your body.    Some people with psoriasis have psoriatic arthritis.
    