Arthur, а 70-yeаr-оld cоllectоr, hаs filled his apartment with antique clocks, old radios, and various pieces of artwork he finds at estate sales, believing each piece has historical significance and might be needed one day. The accumulation has made it difficult for him to move around his apartment or host visitors. His son, worried about his father's safety and wellbeing, consults a mental health professional after Arthur exhibits extreme distress over the idea of parting with any possessions. What is Arthur most likely diagnosed with?