Paget's disease of bone

In Paget's disease the machinery that constantly renews bone goes wrong in a few particular bones. Bone is rebuilt too fast and in disorder: it grows larger and thicker than normal yet ends up coarse and weak. The condition is rare below the age of fifty and becomes commoner with age. It can go years without announcing itself and is often picked up by accident, on a blood test or an X-ray taken for something else entirely.

What happens to the bone

Bone only looks like a fixed scaffold: in fact it is renewed throughout life. One set of cells, the osteoclasts, dissolves worn-out patches, and another, the osteoblasts, lays down new tissue in their place. Normally the two processes balance out and the skeleton keeps both its shape and its strength.

In Paget's disease the osteoclasts in one patch of bone work feverishly and strip tissue away several times faster than usual. The osteoblasts try to keep up and lay down new bone in a hurry, with the fibres arranged haphazardly instead of in orderly layers. The result is bone thicker than normal, coarse-looking on an X-ray, but more likely to break, prone to bending under body weight and threaded with an excess of blood vessels.

One important feature: the disease takes hold in one bone or a few, not throughout the skeleton. New sites do not usually appear later, so what is found on the first set of tests generally marks the limit of the illness.

Which bones are affected and how it feels

The pelvis, thigh bone, shin bone, spine, skull and collarbone are the usual sites. Even so, many people have no symptoms at all, and that is the commonest way the disease behaves.

Where there are symptoms, pain is the usual one, and it has a recognisable character:

• dull, aching and deep, as if coming from inside the bone;
• constant rather than in bouts, and unlike joint pain it does not ease with rest;
• often worse at night and in the warmth of the bed;
• lasting months, without the clear link to activity that arthritis pain has.

The skin over the affected patch may feel warmer than the surrounding area, because remodelled bone takes more blood. Over time the shape changes: the lower leg bows, the spine curves, and a hat or helmet grows tight where the skull is involved. Where the affected patch lies next to a joint, joint pain is added to bone pain, because the uneven bone surface wears the cartilage.

If the skull is involved, hearing loss, ringing in the ears, dizziness and headaches can all follow.

When to see a doctor, and when to go at once

Book an appointment if you have any of the following:

• persistent deep bone or joint pain lasting weeks or months;
• a visible change in the shape of a leg, the back or the head;
• hearing loss or ringing in one ear with no obvious cause;
• a fracture after a minor fall or knock;
• a raised alkaline phosphatase found by chance on a blood test.

Overgrown bone can press on a nerve or on the spinal cord, and that is an emergency. Call an ambulance — in Spain, Italy, Portugal, Poland and Ukraine the single European number is 112 — or go straight to the emergency department if you develop:

• weakness in the legs, which give way or stop obeying;
• numbness around the perineum, the buttocks and the inner thighs;
• inability to pass urine or, conversely, loss of control over bladder or bowel;
• back pain that has suddenly worsened and shoots down both legs.

These signs mean pressure on the spinal cord or the cauda equina. The clock runs in hours: the sooner the pressure is relieved, the better the chance that movement and sensation return in full.

Why it starts

The exact cause is unknown. What is clear is that the fault lies in the osteoclasts themselves: they grow larger, carry more nuclei and lose the ability to stop on time.

Heredity matters appreciably. About one person in seven with the disease has a close relative with the same diagnosis, and genes have been identified in which changes pass the susceptibility on. If a parent, brother or sister had Paget's disease, it is worth telling your doctor: an alkaline phosphatase test is a simple way of checking yourself without waiting for symptoms.

A past viral infection has also been proposed as a trigger, but the evidence for it is not convincing. Neither diet nor exercise nor injury causes the disease, so there is nothing to blame yourself for.

How the diagnosis is reached

The first step is a blood test for alkaline phosphatase. This enzyme is released by bone cells at work, and where remodelling is running hot the level rises, sometimes several times over.

The figure needs reading with two caveats. Alkaline phosphatase does not rise only in bone disease: the liver and bile ducts produce plenty of it, so a high result prompts liver tests to establish where the enzyme is coming from. Conversely, with a small patch of disease, especially a single one, the level can stay normal — a normal result does not rule the condition out.

The diagnosis is confirmed on X-ray. Affected bone looks highly characteristic: thickened, with a coarse outer layer and an irregular pattern of thinned and dense areas. For an experienced radiologist that picture is usually enough.

A bone scan — a small amount of radioactive tracer that gathers wherever remodelling is intense — answers a different question: how many bones are involved and which. It is sensitive but cannot tell why an area lights up, so anything it flags is then looked at on X-ray.

CT and MRI scans are ordered where nerve compression is suspected, where the picture is unclear, and where a tumour has to be excluded. A bone biopsy is rarely needed and only where everything else has left the answer in doubt.

The medicines that slow the remodelling

Paget's disease cannot be cured outright, but it can be settled for years at a time. Where a patch has been found by chance and causes no trouble, treatment is sometimes deferred in favour of monitoring.

The main drugs are bisphosphonates. They damp down the excessive activity of the osteoclasts and remodelling returns to a normal pace. Usually this means a single intravenous infusion; the effect lasts several years, after which the course can be repeated. Tablet forms also exist. Success is judged on two things — whether the pain has gone and whether alkaline phosphatase has fallen — so the blood test is repeated a few months later and then at intervals.

Before the infusion your doctor should check calcium and vitamin D and make good any shortfall, otherwise the calcium level can drop sharply after the drip. Kidney function is checked too. It is worth seeing a dentist beforehand and getting any dental work done: having a tooth out while on bisphosphonates carries a rare but troublesome complication, poor healing of the jaw bone.

After the first infusion a flu-like reaction is common: temperature, aches and headache for a day or two. This is expected, and later infusions are usually milder. With tablets, heartburn and a heavy feeling in the stomach are the more usual complaints.

Easing the pain and taking load off the bone

Pain relief is arranged separately from the main treatment, because bisphosphonates do not take pain away straight away. Paracetamol suits most people. Anti-inflammatory drugs are stronger, but they irritate the stomach, hold on to fluid, raise blood pressure and harm the kidneys, so with an ulcer, heart or kidney failure or in older age they are used cautiously and in short courses rather than taken for months on your own initiative. Calcitonin, once a mainstay, has largely been displaced by bisphosphonates.

Exercise therapy keeps up the strength of the muscles around the affected bone and takes load off it. The programme is best drawn up with a physiotherapist: where a leg or the spine is deformed, not every exercise is suitable, whereas swimming and walking are usually well tolerated.

Simple aids help too: a stick held in the hand opposite the affected leg, insoles that even out a difference in leg length, footwear with a cushioned sole, grab rails in the bathroom. All of it eases pain and cuts the risk of a fall, and a fall in this condition is more dangerous than usual.

Bone needs calcium and vitamin D, from dairy foods, leafy vegetables, fish and sunlight. Supplements are not taken "as a precaution" but on the strength of a blood test, and above all before starting bisphosphonates.

Surgery is needed only occasionally: to fix a broken bone, to replace a worn-out hip or knee, to straighten a badly bent bone or to free a trapped nerve. It is best scheduled once the remodelling has been quietened with drugs, because active bone bleeds heavily.

What the disease can lead to

Complications are far from universal, but their warning signs are worth knowing.

• Fractures. Remodelled bone breaks under modest force. Sometimes a break is preceded by small cracks that give a new, sharp pain on weight-bearing.
• Arthritis of the neighbouring joint. The altered shape of the bone spoils the cartilage, bringing pain on movement, stiffness and grating.
• Deformities. The lower leg bows outwards, the back stoops, the head increases in circumference.
• Hearing loss where the skull is involved, from changes in the small bones of the middle ear and pressure on the hearing nerve. It is worth checking with a hearing test rather than waiting until difficulty in conversation becomes obvious.
• Extra work for the heart. Richly supplied remodelled bone makes the heart pump more blood. With extensive disease and an already damaged heart this occasionally leads to heart failure: breathlessness on exertion, swollen ankles and rapid tiredness.
• Malignant change is the rarest complication, and that is precisely why it must be kept in mind. The warning signs are new or sharply worsening pain in a long-known site, a growing swelling over it, and a rise in alkaline phosphatase after it has been stable for a long time. Changes like these warrant a prompt appointment.

Online consultation

Paget's disease lends itself to remote follow-up: its course is judged from blood tests, imaging and a description of the pain, and all of that can be gone through in an online consultation. The doctor explains what your alkaline phosphatase and its trend mean, whether X-rays need repeating, when treatment is worth discussing, and how to tell bone pain from joint pain.

Have ready every alkaline phosphatase result with its date, X-ray and bone scan reports, a list of medicines including painkillers and supplements, and the date of the last infusion if you have already been treated. Mention whether a parent or sibling had Paget's disease.

Results can be reviewed remotely, pain relief adjusted, monitoring planned and the need for an orthopaedic or hearing specialist decided. But sudden weakness in the legs, trouble passing urine or a suspected fracture are not matters for an online appointment: they need examination and an X-ray without delay.

This material is for information only and does not replace medical advice.