Paget’s disease of bone
What is Paget’s disease of bone?
Paget’s disease of bone (PDB) is a chronic condition of the bone caused by an abnormality in what is called bone remodeling. Bone remodeling is the process by which old bone is removed by cells called osteoclasts and is replaced by cells called osteoblasts. In Paget’s disease, bone remodeling is increased and disorganized. It typically affects one or more bones such as the spine, pelvis, skull and thigh bones. This results in abnormalities of bone structure, enlargement and weakening of the bone. That it turn can lead to pain, deformity and fractures.
Causes of Paget’s disease
The exact cause of Paget’s disease is not completely understood, but on-going research into the area show that genetic factors play a significant role. The risk of developing Paget’s disease is increased 7-10 times in a first degree relative.
It is rarely diagnosed in those over the age of 50 years but becomes more common with increasing age. Paget’s disease is slightly more common in men but can affect both genders. It is particularly prevalent in the UK and other European countries like Spain, France and Italy.
There is some evidence to suggest environmental factors play a role in those that are susceptible to developing Paget’s, these include vitamin D and calcium deficiency in childhood and chronic viral infections.
Symptoms of Paget’s disease
The most common presentation of Paget’s disease is with bone pain, but in about 20% of patients it is picked up as an incidental finding on an x-ray or blood test. The typical abnormality on blood test is an abnormal alkaline phosphatase (ALP) level.
Other symptoms and signs that may occur are:
- Pain localised to an affected site
- Enlargement and of an affected bone
- Warmth of an affected bone (typically the shin bone or tibia)
- Arthritis of a joint next to an affected bone
- Broken bone (fracture)
- Deafness (if the skull is involved)
- Back pain with radiation down the leg if the spine is involved
- Rare complications are:
- High blood calcium (associated with being immobile and dehydrated)
- Bone tumours (less than 0.1% of patients)
How do we diagnose Paget’s disease?
Paget’s disease is usually diagnosed from blood tests and imaging. The most common investigations are listed below:
- Alkaline phosphatase
- This is usually increased in active Paget’s disease. Although it isn’t always specific and can be raised for other reasons.
- These can show expansion of bone due to increased remodelling and changes in the structure of the bone including deformity.
- Radionuclide bone scans
- An injection of radioactive isotope is given into a vein and makes its way to very active areas of bone. A special camera scans this and can show where the areas of Paget’s disease are.
If Paget’s disease is diagnosed incidentally with no symptoms, then no treatment may be required.
The first line treatment are drugs called bisphosphonates. These can be taken as a course of tablets taken daily for 2 months (risedronate) or as a drip into a vein (zoledronic acid or pamidronate). Vitamin D supplements are often required prior to bisphosphonate injections being given.
Painkillers such as paracetamol or anti-inflammatory drugs (NSAIDs) may also be required, particularly in people with co-existing osteoarthritis.
Orthopaedic surgery is required in about 10% of patients to replace joints in people with arthritis of joints close to affected bones and to fix fractures. The outcome of orthopaedic surgery in PDB is usually excellent.
Disease activity is monitored by symptoms and measuring the blood marker alkaline phosphatase every 6 to 12 months.
Versus Arthritis: http://www.versusarthritis.org
Paget’s Association: http://www.paget.org.uk