Among the many changes made in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, published earlier this month, is the addition of hoarding, recognized as its own disorder.
Prior to the DSM-5, hoarding was considered a form of obsessive-compulsive disorder (OCD), but now the American Psychiatric Association—the organization behind the "bible" of mental health—has given pathological collecting its own diagnosis, since hoarding isn't actually a symptom of OCD. Additionally, brain scans reveal that hoarders have a different neurobiology.
The difference between normal collections and hoarding disorder is that hoarders "hang on to items, because they fear they will need them at some point in the future. They may also feel excessively attached to, or overvalue the worth of, these possessions."
Normal or Not? When Collecting Becomes Hoarding [Live Science]