Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Collagenous colitis ?
    ### Response:
    Collagenous colitis is a type of inflammatory bowel disease that affects the colon. It is a form of microscopic colitis, which means that the inflammation is only visible when a biopsy is examined under a microscope; the inflammation cannot be seen or diagnosed from colonoscopy or sigmoidoscopy.
    