Which condition involves the replacement of normal bone with abnormal bone tissue?

Paget’s disease is characterized by the replacement of normal bone with abnormal bone tissue, resulting in enlarged and deformed bones. This condition leads to a disruption in the normal bone remodeling process, where old bone is replaced with new bone. In Paget's disease, the new bone is often weaker and more prone to fractures, and it may have an irregular structure. This condition primarily affects older adults and can lead to a variety of symptoms depending on the bones involved.

The other conditions listed do not specifically involve the abnormal replacement of normal bone tissue in the same manner as Paget’s disease. Osteogenesis imperfecta is a genetic disorder that affects collagen production, leading to brittle bones. Multiple myeloma is a type of cancer that originates in plasma cells and often leads to bone damage, but it does not involve the replacement of normal bone tissue with abnormal tissue in the sense that Paget’s disease does. Fibrous dysplasia is a condition where bone is replaced by fibrous tissue, but it is not characterized by the abnormal remodeling and remodeling disruption seen in Paget’s disease.