Calcium crystal diseases (pseudogout)

What are calcium crystal diseases?

It's normal for calcium crystals to be found in parts of your body such as your bones and teeth, but when they occur in and around your joints they can sometimes cause sudden (acute) attacks of painful inflammation. The main crystals that cause problems are calcium pyrophosphate (CPP) crystals and apatite crystals, and the problems they cause are referred to collectively as calcium crystal diseases.

There are two types of calcium crystals that can potentially cause problems:

  • calcium pyrophosphate (CPP) crystals, which can build up in the joint cartilage – this is known as cartilage calcification or chondrocalcinosis
  • apatite crystals, which occasionally build up in the joint cartilage but more commonly in a tendon, this is known as calcific tendinitis.

Sometimes chondrocalcinosis involves a mix of CPP and apatite crystals.

In many cases, these crystals occur in otherwise normal cartilage or tendons without causing any symptoms at all. If the crystals are embedded deep in the tissues they don't usually affect the way the tissues work. And because they're deep within the tissues they don't come into contact with your blood cells or the proteins involved in the immune system and therefore don't cause inflammation. Many people have crystal deposits in these tissues for years without having any problems.

However, crystals can cause attacks of painful inflammation if they shake loose:

  • from the cartilage into the joint cavity, or
  • from a tendon into the surrounding soft tissues.

This movement of crystals is called crystal shedding, and the inflammation occurs because the crystals are exposed to the body's immune system.

When CPP crystals shed into the joint cavity this is called acute calcium pyrophosphate (CPP) arthritis. The crystals cause inflammation in the lining of the joint, resulting in pain and swelling in the joint. The condition was previously known as pseudogout, meaning 'false-gout' because the inflammation resembles gout (a condition caused by urate crystals).

When apatite crystals are shed into soft tissues surrounding a tendon this is called acute calcific tendinitis or acute periarthritis. It most commonly affects the supraspinatus tendon in the shoulder, but can affect tendons anywhere in the body.

Who gets calcium crystal diseases?

Acute CPP crystal arthritis usually affects people in late middle-age or the elderly, and it’s rare if you’re under the age of 60. Men and women are equally affected. An attack of acute CPP crystal arthritis can happen in a joint that’s already affected by osteoarthritis.

Acute calcific tendinitis usually affects the shoulders of young or middle-aged adults. Again, men and women are equally affected.

Symptoms

The two most common types of calcium crystal disease, acute CPP crystal arthritis (pseudogout), and acute calcific tendinitis (acute periarthritis), have different symptoms.

Symptoms of acute CPP crystal arthritis include:

  • sudden pain and stiffness in affected joint (most commonly the knee)
  • swelling and tenderness
  • red, inflamed skin over the joint
  • raised temperature
  • generally feeling unwell

These symptoms tend to last several days to 2 weeks before completely settling.

Symptoms of acute calcific tendinitis include:

  • painful swelling around the joint (most commonly in the shoulder)
  • bulging tendons due to crystal deposits
  • redness and tenderness around the joint

These symptoms usually settle back to normal after 2-4 weeks.

Causes

Why do people get calcium crystal deposits?

Crystals are made up of very small geometric particles (atoms) arranged in a regular repeating pattern. This makes them very hard and difficult to break down. In certain substances this is helpful, for example, it contributes to the strength of bone and seashells. However, the hard sharp angles of calcium crystals can rub and grind down softer substances that come into contact with them. In addition, their rough surface has a strong electrical charge, which can injure cells and trigger an immune reaction (inflammation).

Even if you're perfectly healthy, the chemicals that form crystals may be present in your blood, urine or soft tissues. Other chemicals within the body either promote or inhibit the formation of crystals, and the balance between these chemicals tends to change as part of normal ageing. These changes are mainly localised to particular parts of the body and are the most likely reason for crystals forming.

Other possible causes of calcium crystal diseases are:

  • metabolic diseases which affect the regulation of calcium or polyphosphate levels, including:
    • hyperparathyroidism (overactivity of the parathyroid glands)
    • haemochromatosis (also known as iron-storage disease)
    • hypomagnesaemia (magnesium deficiency)
  • genetic factors, recent research has found that an abnormality of the ANKH gene may lead to the production of too much pyrophosphate, which can result in widespread calcium crystal depositing. This can cause recurrent attacks of acute CPP crystal arthritis at an unusually young age (20s or 30s).

Uncommon causes of calcific tendinitis include diabetes, the kidneys not working properly or high calcium levels.

What triggers acute attacks?

Many attacks of acute CPP crystal arthritis and acute calcific tendinitis occur for no obvious reason, and it’s not clear why the crystals have been shed. But sometimes there’ll be something that has provoked the attack. For example, an injury to your knee or shoulder may shake the crystals loose, setting off an attack a day or two afterwards. Another common trigger is an illness that causes a fever, such as having flu or a chest infection. For some reason these illnesses encourage crystal shedding, leading to an acute attack. A major stress to your body such as having an operation or a heart attack may also trigger an attack.

Diagnosis

Your doctor will probably need to carry out some tests to rule out other conditions, such as gout or infections.

What tests are there?

There are several tests that can be carried out to help diagnose calcium crystal diseases, including:

  • testing the joint fluid for crystals and infection
  • x-rays to show any calcification in the joint cartilage or tendon
  • blood tests to assess the level of inflammation, the calcium level, to check that the problem isn’t caused by infections and to check that your kidneys are working normally.

Treatments

Attacks of acute CPP crystal arthritis or acute calcific tendinitis will usually settle on their own without any treatment. However, because the attacks are so painful and distressing, treatment is usually required to relieve pain, reduce inflammation and speed up recovery.

Drugs

Your doctor may prescribe non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, naproxen or diclofenac, which can help to ease the pain of an acute attack. For the intense pain of an acute attack, these will need to be prescribed at a high dose.

NSAIDs can cause digestive problems (stomach upsets, indigestion or damage to the lining of the stomach), so in most cases they’ll be given along with a drug called a proton pump inhibitor (PPI), which will help to protect your stomach. NSAIDs also carry an increased risk of heart attack or stroke. Although the increased risk is small, your doctor will be cautious about prescribing NSAIDs if there are other factors that may increase your overall risk, for example, smoking, circulation problems, high blood pressure, high cholesterol or diabetes.

Another treatment that's sometime used is colchicine. This drug is also used to treat acute gout and works by reducing the interaction between the crystals and your immune system. The usual dose is 0.5 mg 2-4 times a day, which is usually very effective and well tolerated. The most common side-effect is loose bowel motions, but higher doses can cause more severe diarrhoea.

Managing symptoms

Learn more about how to manage the symptoms of calcium crystal diseases.

Exercise

Following an attack of inflammation it’s important that you get the affected joint and muscles moving through their normal range of motion as soon as possible. Doing a small amount of exercise on a regular basis will prevent any weakening or wasting of surrounding muscle and help the inflamed tissues return to normal. Your physiotherapist can help you and give expert advice. If you have osteoarthritis with CPPD, you should do regular strengthening exercises and aerobic exercises.

Read more about exercise and arthritis.

The difference between osteoarthritis with crystals and osteoarthritis without crystals

Many people with osteoarthritis, particularly of the knee, have calcium pyrophosphate crystals in their affected joint cartilage, often in the knee. This combination is called osteoarthritis with calcium pyrophosphate crystal deposition (osteoarthritis with CPPD for short).

CPP crystals tend to make your osteoarthritis worse. The affected joints are likely to become more painful and stiff than an osteoarthritic joint without calcium crystals. The narrowing of cartilage and thickening of bone associated with osteoarthritis are also more likely to progress over several years when crystals are present. You may have attacks of acute CPP crystal arthritis in these joints.