Paget's Disease of Bone

Understanding normal bone

Bone is a living tissue. There are two main types of cells within the hard bone material. One type called osteoblasts makes and lays down bone material. Another type called osteoclasts resorbs ('dissolves') particles of bone. These cells are active throughout life. They work in a balanced way to make and mould bone, repair damage, and keep the bone structure correctly 'woven'. There is a slow but constant turnover of bone.

What is Paget's disease?

Paget's disease of bone was first described by Sir James Paget in 1877. (It is a different condition to Paget's disease of the breast. This leaflet is only about Paget's disease of bone.)

In Paget's disease the bone making process (the bone turnover) gets faster and out of control. Affected areas of bone form new bone material in an abnormal way. The newly formed bone is thicker than normal and the bone may become wider. However, the bone is not made properly and it is weaker than normal bone. This can cause deformity of the affected bone, particularly in weight bearing bones such as the leg bones which may bend. Affected bone is also more likely to fracture (break).

What causes Paget's disease of bone?

The underlying cause is a problem with the osteoclasts (one of the bone cells). In affected areas of bone there are abnormal osteoclasts which are bigger than normal. It is thought that these are wrongly 'programmed' in the way they mould bone. More bone than normal is resorbed ('dissolved') by the abnormal osteoclasts. As a response to this the osteoblasts increase in activity to make new bone material. But this increase in bone turnover leads to badly structured areas of bone that are wrongly 'woven'.

How the osteoclasts in a localised area of bone become out of control is not known. One theory is that they may become infected with a virus which alters them in some way. There also seems to be some genetic factors. Up to 4 in 10 people with Paget's disease have a close relative (parent, mother, brother, sister) who also develops the disease. One theory is that your genetic make-up makes you prone to this disease, but it may need to be triggered by a certain virus.

Who gets Paget's disease of bone?

It mainly affects people aged over 50. The disease affects three men for every two women. One study found that up to 8 in 100 people in the UK over the age of 55 had some X-ray changes of Paget's disease in one or more of their bones. It becomes more common with increasing age. Nearly 1 in 10 people in their 80s are thought to have some degree of Paget's disease. However, most people with Paget's disease have no symptoms and will not be aware they have the condition.

What are the symptoms of Paget's disease of bone?

One or more bones may be affected. The bones most commonly affected are the pelvis, the femur (upper leg), the vertebrae of the spine, and the skull. Other bones are less commonly affected. The abnormality of bone formation starts in one point on a bone. It then gradually spreads along the bone at up to 12 mm per year. This may lead to one or more of the following.

In many cases there are no symptoms

More than 9 in 10 people with Paget's disease have no symptoms. The abnormal structure of bone is localised and may never cause any problems. The disease is commonly found by chance when an X-ray is taken for another reason.

Pain

This is the most common symptom if symptoms do occur. The pain is typically a deep seated ache of the bone that is usually not affected by rest or exercise. It is commonly worse at night. It may be mild but can become severe. Shooting pains from the affected area may also occur.

Deformity

A deformity may develop, depending on the site of the disease and the size of the affected part of the bone. Bowing of the upper leg is the most common when the femur (thigh bone) is affected. Bowing of the tibia (lower part of leg) can lead to a deformity called 'sabre tibia'. Another example is an odd shape to the head that may develop if the skull is affected.

Fractures

Affected bones are more liable to fracture (break). A fracture after a minor fall or injury may be the first indication that Paget's disease has developed.

Nerve compression

Abnormal overgrowth of a bone may press on nearby nerves. This can cause a variety of symptoms. For example, neuralgic pain (a different type of pain to the more common 'bone pain' of Paget's disease). Another quite common symptom if the skull is affected is deafness of one ear. This is caused by pressure on the ear nerve that goes through an affected skull bone.

Other possible problems include weakness of muscles supplied by a compressed nerve, or numbness of an area of skin supplied by a compressed nerve.

Arthritis (joint inflammation)

This may develop if an affected section of bone is next to a joint.

Some rare complications of Paget's disease

For the sake of completeness, the following are some possible, but rare, complications.

Heart failure

If large areas of bone throughout the body are affected then you need a lot of blood flow to the affected bone. This can cause problems to the heart as it needs to deliver this extra blood flow and heart failure may develop.

Vascular steal syndrome

If the skull is extensively affected, then the extra blood flow needed to supply the enlarged skull may be 'stolen' from the blood supply going to the brain. This may result in you becoming tired and listless. A similar effect can occur if a large area of spine is involved and blood flow to the the spinal cord may be 'stolen' and diverted to the affected bone. This may cause various symptoms such as numbness and weakness of parts of the body supplied by nerves from the affected part of the spinal cord.

Bone cancer

Abnormal bone can, occasionally, turn cancerous. This is thought to occur in less than 1 in 200 people with Paget's disease. Bone cancer may be suspected if you develop worsening pain or swelling over an affected area of bone.

Other

The high bone turnover may cause high blood levels of various chemicals. Rarely, this leads to problems such as gout or a high blood calcium level which can cause various symptoms.

How is Paget's disease diagnosed?

• X-ray. A bone with Paget's disease can usually be seen quite easily on an X-ray. The X-ray may be done if the disease is suspected by your doctor (if you have pain, etc). More often, it is seen by chance when an X-ray is done for another reason.
• Bone scan. This may be done if an area of Paget's disease is found in one bone. This test involves an injection of a radioisotope ('radioactive chemical'). This is taken up into bone but much more readily by areas of Paget's disease with a high bone turnover. A scan then detects the level of radioactivity coming from each bone. High readings come from affected bones. Therefore this test can detect which bones are affected throughout the body.
• Blood tests. A chemical in the blood called alkaline phosphatase can be measured in a blood sample. This rises with increasing bone turnover. The level of this gives some idea of the activity of the disease and how extensive it is throughout the body. This blood test is also useful to see how well treatment is working. The level falls when treatment is working and bone turnover falls. This blood test may be advised every six months if treatment is given to check that treatment continues to work.

What is the treatment for Paget's disease?

No treatment is needed in many cases. In most cases the disease is found by chance, does not cause symptoms, and often does not need treatment. Treatment may be advised if symptoms such as pain or bone deformity develops. Also, treatment may be advised if you do not have symptoms, but where the site of the disease may cause problems as the disease progresses. For example, if you have an area of Paget's disease at the base of the skull. Progression of the disease here, if left untreated, may result in compression of the ear nerve and cause deafness.

Your specialist will advise on whether treatment is necessary.

Bisphosphonate medicines

If treatment is advised, a bisphosphonate medicine is the usual treatment given. There are several types which include: etidronate, pamidronate, tiludronate, risedronate, clodronate, alendronate, ibandronate and zoledronate. Bisphosphonates work by reducing the abnormal bone turnover. This results in any new bone formation to be more normal in structure. They have an effect on existing disease to reduce pain although this may take several months of treatment. Treatment is good at preventing further progression of the disease.

A course of treatment usually lasts several weeks or months. This often has a knock-on effect for several months or years. Most of the bisphosphonates are taken as tablets, but pamidronate and zoledronate are given by injection. But note: treatment with zoledronate is just one injection yearly.

If you take bisphosphonate tablets, it is vital that you take them exactly as instructed. Read the leaflet that comes with the tablets for details on how to take the tablets. For example, one instruction will be not to take the tablets with food or drink containing calcium. This is because the absorption of bisphosphonates from the gut is affected by calcium.

Like all medicines, bisphosphonate medicines may cause side-effects but generally they are well tolerated and work well. The leaflet that comes with the tablet packet gives a full list of possible side effects. Tell your doctor if you have side-effects when taking a bisphosphonate as an alternative one may be better.

One potential problem to consider with bisphosphonates - osteonecrosis of the jaw
Osteonecrosis (bone destruction) of the jaw is a rare complication that affects a small number of people who are treated with a bisphosphonate. The main symptoms of osteonecrosis of the jaw include pain, numbness, or a heaviness of the jaw, gum infections and loosening of teeth. It may eventually lead to disfigurement of the jaw. Osteonecrosis of the jaw mostly occurs in people who have been treated with a bisphosphonate for a number of years. Also, the risk is increased if you are on chemotherapy or steroid medication for other conditions, or if you have dental treatment.

Therefore:

• It is best to have any dental treatment done before you commence treatment with a bisphosphonate.
• If you are being treated with a bisphosphonate, tell your doctor or dentist as soon as possible if you develop any gum, tooth or jaw symptoms.
• Tell your dentist that you are taking a bisphosphonate before any dental work.
• Maintain good oral and dental hygiene.

Other treatments

Various other treatments may be advised, depending on your circumstances. For example:

• Painkillers if the disease is causing pain. The painkillers used may be different for bone pain and neuralgic pain - two different types of pain which may occur.
• Calcitonin is a medicine that also reduces bone turnover. It was used before biphosphonates were developed. It is less effective than these newer medicines and is not used so much now.
• Surgery may be needed if the disease has caused deformity or damaged a joint. For example, joint replacement surgery may be an option if a bone near to a joint is affected and has caused bad arthritis.

Further help and information

National Association for the Relief of Paget's Disease

323 Manchester Road, Walkden, Worsley, Manchester, M28 3HH
Tel: 0161 799 4646 Web: www.paget.org.uk