Question

Discuss the phases of Paget’s disease and the expected pathological changes in bone

Answer 1

Paget’s disease

Paget’s disease is a condition in which there is a partial or complete involvement of single or multiple bones involved in the cellular remodeling and deformity of the bones. In this condition, there is an excessive bone breakdown and regrowth of new bone. These changes will lead the bone to weaken, which may result in deformity, pain, or fracture of associated joints.

Phases of Paget’s disease

There are three phases in Paget’s disease. They are:

Lytic phase, mixed lytic and blastic phase, and Sclerotic phase

• Lytic phase

The lytic phase, this phase is considered as the initial phase of Paget’s disease in which the bone is resorbed by the osteoclasts which are more numerous, larger, and having more nuclei up to 100. The bone turnover rate will increase 20 times more than normal. There will be an increased blood flow to the bones which are involved in this condition.

• Mixed lytic and blastic phase

In this phase, there will be a rapid increase in bone formation from the numerous osteoblasts. Although there is an increase in bone formation, morphologically they are normal. These newly formed bones will appear as abnormal and the collagen fibers will deposit in a haphazard fashion rather than the linear fashion. Once the osteoclastic and osteoblastic activities for the bone destruction and bone formation repeats, there will be a high degree of bone turnover will occur.

• Sclerotic phase

This phase is considered the final phase of Paget’s disease. In this phase, the bone formation dominates and there is a disorganized woven pattern. These bones are weaker than the normal one. This woven pattern will lead to a hypervascular bone state by allowing the bone marrow to be infiltrated by the blood vessels and the connective tissues.

Slowly the osteoclastic activity will decrease but the abnormal bone formation continues. Finally, the osteoblastic activity will also decrease and enters the sclerotic or burned out phase. The bone absorption becomes minimal or absent in this phase.