Calcium crystal diseases (pseudogout)

Crystals can form either in the cartilage within a joint or in tendons that anchor the muscles to the bones, causing:

• Cartilage calcification (or chondrocalcinosis) – The knee is by far the most commonly affected joint, but it can also occur at the wrist, shoulder or other joints. This is usually caused by calcium pyrophosphate crystals.
• Calcific tendinitis – This is caused by apatite crystals and most often affects the shoulder although it can also occur in the hip, the hand, or other parts of the body.

Many people have crystal deposits without having any symptoms. Sometimes a large deposit of apatite causes swelling that restricts movement, but this is unusual. While the crystals are embedded deep in the cartilage or tendon they don't usually interfere with the working of these tissues and they don't come into contact with blood cells or proteins involved in the body's defence mechanism.

Often, it is when the crystals move out into the joint cavity or the soft tissues surrounding a tendon, that problems arise. This is known as crystal shedding. The crystals have a rough, abrasive surface with a strong electrical charge which can injure cells and trigger off the body's defence mechanisms, causing sudden (acute) attacks of severe inflammation. These attacks are known as:

• acute calcium pyrophosphate crystal arthritis (or pseudogout) when the joint itself is affected
• acute calcific tendinitis (or acute periarthritis) when the surrounding tissues are affected.

Sometimes the shedding of crystals seems to have been triggered by illness, an injury, or a major stress to the body such as an operation or a heart attack, but often there is no obvious reason for the acute attack.

Osteoarthritis with calcium crystals

Many people with osteoarthritis have calcium pyrophosphate crystals in their joint cartilage. This is particularly common with osteoarthritis of the knee. Osteoarthritis with crystals is sometimes called chronic pyrophosphate arthritis.

The presence of crystals tends to make the symptoms of osteoarthritis worse – the joints are more painful and stiff than they would otherwise be. The thinning of cartilage and thickening of bone that are associated with osteoarthritis are also more likely to progress when crystals are present.

The joints may also develop attacks of acute CPP crystal arthritis, as well as the more long-standing symptoms caused by osteoarthritis.

It usually affects only one joint at a time, and is most likely to occur in the knee. Attacks of pseudogout are often precipitated by another illness or an operation. They may be the first sign that anything is wrong with the joint, but can also occur in osteoarthritic joints causing an apparent worsening of the arthritis.

The swelling is mainly due to fluid collecting in the joint. This build-up of pressure makes the joint very tense, stiff and painful to move. The skin often appears reddened, tight and shiny. You may also feel generally unwell and have a raised temperature.

The typical attack gradually settles on its own, even without any treatment. The swelling usually starts going down within a week, though the joint may be very painful and take up to 2–3 weeks to return to normal.

When the condition affects the shoulder, you will feel pain mainly over the upper arm and shoulder, which is made worse by trying to raise the arm outwards. You may have swelling, redness and tenderness over the angle of the shoulder, and the swelling may occasionally extend to the upper arm. It's possible, in some cases, for the subacromial bursa (the fluid-filled sac below the acromion) to burst, causing bruising in the arm as far as the elbow.

The acute pain gradually settles on its own, but it may take 2–4 weeks before the affected area gets back to normal.

Even in healthy people, certain chemicals may be present in the blood, urine or soft tissues at levels that are, in theory, high enough for crystals to form.

Whether or not crystals do form in the body tissues depends on the balance between substances that promote the formation of crystals and substances that inhibit crystal formation. This balance tends to alter as we age, so we are more likely to develop crystals as we get older. Osteoarthritis can also alter the balance and increase the chances of crystals forming.

The tendency to develop chondrocalcinosis and acute CPP crystal arthritis sometimes runs in families. In some cases, abnormality in a particular gene (the ANKH gene) may lead to excessive production of pyrophosphate, which can result in widespread chondrocalcinosis and a type of acute CPP crystal arthritis that starts at a much younger age (in the early 20s or even late teens).

Far less commonly, chondrocalcinosis may be due to a metabolic disease that interferes with the regulation of calcium or pyrophosphate levels. Examples are conditions such as hyperparathyroidism (overactivity of the parathyroid glands), haemochromatosis (iron-storage disease) and hypomagnesaemia (magnesium deficiency).

Calcific tendinitis can sometimes be caused by other conditions such as diabetes, the kidneys not working properly, or unusually high calcium levels. And there are some types of calcific tendinitis that seem to run in families, although the reasons for this are not yet known.

What tests are there?

An x-ray can also be helpful in showing calcification in the joint cartilage or in the tendon. Occasionally a repeat x-ray is taken a few weeks later to check whether the calcification has decreased.

Blood tests are often taken during the attack to assess the level of inflammation and to make sure the problem isn't caused by an infection. A blood test can also be used to check calcium levels and to make sure the kidneys are working normally.

Younger people (under 55) who develop acute CPP crystal arthritis, or people with significant chondrocalcinosis in a number of joints, may have other blood tests and x-rays to check for underlying problems that may have caused the crystal deposits.

Acute CPP arthritis (pseudogout) treatments

A number of measures can reduce the severe pain and inflammation:

• Applying an ice-pack around the painful joint will take the edge off the severe pain.
• Drawing off fluid from the joint using a needle (aspiration) can quickly reduce the pressure in the joint that is causing the pain. This may be all that is needed to bring relief quickly. Sometimes, once the fluid has been drawn out your doctor will inject a small amount of a long-acting steroid into the joint. This helps to reduce inflammation and prevent the build-up of more fluid.
• Simple painkillers (analgesics) such as paracetamol may help with pain relief, but some people will need combined analgesics – such as paracetamol combined with codeine.
• Non-steroidal anti-inflammatory drugs (NSAIDs) may be given to provide pain relief.
• Colchicine is occasionally used to reduce inflammation.
• Washing out the knee joint in hospital (lavage) is also used occasionally.

Acute calcific tendinitis treatments

Acute calcific tendinitis is mainly treated with ice-packs, painkillers and NSAIDs. If there is a large build-up of fluid in either the subacromial or subdeltoid bursa (fluid-filled sacs in the shoulder) this can be aspirated, and occasionally injected with steroid.

Is there any need for long-term treatment?

Once the attack is over there's usually no need for any long-term treatment. If acute CPP crystal arthritis keeps coming back and the attacks are very troublesome, low-dose daily colchicine can be taken on a regular basis to reduce their frequency and severity.

Surgery is sometimes needed to remove very large crystal deposits from tendons, but this is only necessary if swelling is causing the tendons to become trapped when the joint is moved (impingement).

Exercise

Once an attack of acute CPP crystal arthritis (pseudogout) or calcific tendinitis has been brought under control, it's important that you get the affected joint and muscles moving normally as soon as possible.

Regular exercise will prevent any weakening or wasting of surrounding muscle and help the inflamed tissues return to normal. Your physiotherapist can give expert advice on suitable exercises.

Read more general advice and specific exercises that will help you keep active.

Diet and nutrition

Generally, diet seems to have very little effect on deposits of apatite or calcium pyrophosphate crystal. Special diets and supplements are needed only for the very few people who have a metabolic disease (such as magnesium deficiency) or kidney problems that might make them more likely to develop crystals.