Paget's disease of bone

Bone is a living, active tissue that is constantly renewing itself. Old bone is broken down by cells called osteoclasts and replaced by new bone produced by cells called osteoblasts. This turnover of bone is finely balanced; otherwise bones would be much more prone to fracture.

Paget's disease alters the way new bone develops.

• Bone cells increase in number, and become larger and more active.
• Bone turnover increases by up to forty times.
• The new bone is abnormal in shape and structure, and is weaker than usual.

The bones most commonly affected are the thigh and shin bones, the pelvis and spine, and the skull.

Paget's disease can sometimes be associated with osteoarthritis in the joints nearby. Paget's disease increases the flow of blood through the bone and as a result parts of the body affected by Paget's disease may feel unusually warm to the touch.

In time, Paget's disease can lead to a number of other symptoms or complications that are potentially more serious:

• Bone expansion – Bone that is affected by Paget's disease expands and may become deformed due to the unusual cell activity. This is most common in the pelvic bones, the spine, and the thigh and shin bones. Long bones can curve so that one leg may end up shorter than the other
• Fractures – Although bone affected by Paget's disease expands, it is weaker than usual and is more likely to break than normal healthy bone
• Nerve compression – When Pagetic bone expands it can sometimes squeeze nearby nerves. This can happen in the skull, where it can cause deafness, or in the spine, which can lead to weakness and tingling in the legs
• Deafness – People who have Paget's disease of the bones in the head can sometimes become hard of hearing or develop deafness. This seems to be caused by thickening of the bones around the ear.
• Osteoarthritis – If the disease reaches to the end of the bone, it can lead to osteoarthritis in the joint, resulting in pain and stiffness on moving the joint
• Tumours – In a very small number of people with longstanding Paget's disease tumours may develop in the bone, which can sometimes be cancerous. The first signs of this are increased pain and swelling at the site of the tumour. However, this is a very rare complication.

There's some evidence that lifestyle factors play a part – for example, poor diet or bone injury early in life may act as triggers for the later development of Paget's in people who also have genetic risk factors.

Another theory is that Paget's disease may be linked to a viral infection early in life, though this remains controversial.

Sometimes the doctor will ask for an isotope bone scan. This is the most effective way of pinpointing where the affected  bone is and how active it is. A tiny dose of radioactive isotope, which can be detected by the bone scan, is injected into a vein and the whole skeleton is scanned several hours later. The radioactive material quickly passes out of the body in the urine.

Once the diagnosis has been made, most patients will be referred to a specialist clinic for assessment and treatment.

Paget's disease drugs

Paget's disease is often treated with a group of drugs called bisphosphonates. These act primarily on the osteoclasts (the bone-eroding cells) to slow down the rapid bone turnover. Drugs in this group include:

• pamidronate, which is injected into a vein – either as a series of weekly or fortnightly injections, or as a single injection which can be repeated after six months if necessary
• zoledronic acid, which is given as a single injection and which may be effective for up to two years
• risedronate, which is given as a two-month course of tablets
• tiludronate, which is given as a three-month course of tablets
• etidronate, which is given as a three-month course of tablets.

The advantage of injections is that the drug is all absorbed into the body but the disease can be treated with tablets. These must be taken on an empty stomach, otherwise they will not be absorbed into the blood stream. If you are taking bisphosphonates orally you should not do so within two hours either side of a calcium supplement as calcium can reduce the amount of bisphosphonate absorbed into the body.

Bisphosphonates are often effective at relieving bone pain due to Paget's disease, but often it takes several weeks for symptoms to improve.

Further courses of bisphosphonates may be necessary if symptoms recur.

Paget's disease can also be treated with a drug called calcitonin, which can be given as a nasal spray or a daily injection, although this is used less frequently than bisphosphonates.

Most patients also require painkillers such as paracetamol and/or non-steroidal anti-inflammatory drugs (NSAIDs) which can be effective at reducing pain, especially when it is caused by osteoarthritis and nerve compression.

Physical therapies

A therapy assessment, generally by a physiotherapist, can be very helpful. It may, for example, identify whether one leg has effectively been shortened because the thigh and shin bones have grown curved. In this case a built-up insole in the shoe can reduce the feeling of lop-sidedness. Physiotherapists can also advise on muscle-strengthening exercise which may be of benefit, while an occupational therapist can offer advice on walking aids and other aspects of daily living.

Surgery

Surgery is not normally necessary, but sometimes if the bone breaks an operation will be needed to fix it, depending on the type and severity of the break. If osteoarthritis results from the disease then a new joint may sometimes be necessary.