A 58-year-old woman is referred by Adult Protective Services after a home visit revealed rooms filled floor-to-ceiling with newspapers, clothing, and broken appliances, with only narrow pathways between rooms. She becomes extremely distressed at the thought of discarding any item, stating each has sentimental value or might be useful someday. She reports genuine pleasure when acquiring new items at yard sales and feels strong emotional attachment to her possessions. She denies any intrusive, unwanted thoughts driving the accumulation, and she does not view the saving behavior as senseless or excessive. The most accurate diagnosis is: