Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Tracheobronchopathia osteoplastica ?
    ### Response:
    What causes tracheobronchopathia osteoplastica? The underlying cause of tracheobronchopathia osteoplastica (TO) remains unknown. Several theories have been proposed, including chronic airway inflammation, exostosis (formation of new bone), and metaplasia (abnormal cell changes) in the affected tissue.
    