Paget disease of the bone is a chronic condition that causes the bones to become dense, enlarged and deformed, leading to fragile bones that fracture. It is the most common bone disorder after osteoporosis in adults after the age of 50. The risk of Paget’s disease of bone increases with age and with family history.
Bone remodeling is defined as a process in which new bone tissue replaces old bone tissue. This process is affected by Paget’s disease, resulting in dense but brittle bones. It most commonly affects the pelvis, skull, spine, and legs. Complications of Paget’s disease of bone can include broken bones, hearing loss and pinched nerves in your spine.
There are two types of Paget’s disease of bone: monostotic (when only one bone is affected), or polyostotic (when multiple bones are involved).
The exact cause of Paget disease of the bone is not known, but genetics are thought to play a role.
There is some evidence that viral infection may also have a role in its development. Proteins derived from the respiratory syncytial virus and measles virus are present in pagetic osteoclasts. Paget’s disease tends to aggregate in families. First-degree relatives of patients with Paget ’s have a 7- to 10-fold increased risk of developing the condition.
While about 70% of patients with PDB are asymptomatic, in the remaining cases, it presents with joint inflammation, bone deformity, pain, and predisposition to fractures.
Paget’s disease can cause skeletal deformities, such as bowing of long bones, enlarged skull, pelvic alterations, and osteoarthritis. It can lead to traumatic and pathologic fractures. Very rarely, it can lead to osteosarcomas, which have a poor prognosis (5-year survival rate of approximately 10%). Paget’s is also associated with neurologic complications, such as deafness, facial nerve palsies, radiculopathies, and spinal cord compression. If it affects the skull, that can lead to hydrocephalus, nerve entrapment, and cerebellar dysfunction, causing the symptoms of nausea, ataxia, incontinence, gait disturbance, or dementia. It is also associated with high cardiac output, hypercalcemia, and hyperparathyroidism, but these are all rare.
Tests that can be done to confirm/support the diagnosis include:
- Serum alkaline phosphatase: these levels are raised in any condition of bone growth or an increased activity of bone cells.
- Bone scan: This is a nuclear imaging test that shows blood flow to the bone and cell activity within the bone, which helps determine areas of abnormally high bone turnover. It detects up to 50% more lesions than seen on x-ray films.
- X-ray films: It is the main mode of its diagnosis. It shows osteolytic, osteoblastic, or mixed lesions. Other characteristic features include transverse lucent areas, enlargement of bones, expanding lytic changes, thickened cortices, or osteoporosis with lytic involvement in the skull.
- Bone biopsy: These may be done to confirm the diagnosis through tissue assessment, but they are mostly done if the malignant transformation of the bone is suspected, which is characterized by cortical destruction and the presence of a soft tissue mass outside of the bone.
Treatment is targeted at suppressing osteoclastic activity. The most commonly used agents are the bisphosphonates (such as Etidronate) that inhibit bone resorption. Intravenous options are also available, such as pamidronate. Salmon and human calcitonin are also FDA-approved and are given subcutaneously.