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What are calcium crystal diseases?

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.

Calcific tendinitis of the shoulder

The knee joint showing chondrocalcinosis

Shedding of crystals from cartilage into the joint capsule

Shedding of crystals from a tendon in the shoulder

For more information, go to www.arthritisresearchuk.org.
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