What is acute CPP crystal arthritis?
Acute calcium pyrophosphate (CPP) crystal arthritis is a condition that can cause pain and swelling in joints.
It’s known as a calcium crystal disease because the pain is caused by crystals of the mineral calcium rubbing against soft tissue.
It most commonly affects the knees, but can affect other joints too.
Calcium crystals are normally in bones and teeth to help make them strong. However, people can have too much of these crystals and in the wrong place in the body, and this can cause problems.
In acute CPP crystal arthritis they can form in the cartilage at the ends of bones.
Many people can have calcium crystals in their cartilage for years without them causing any problems.
However, these crystals can move from their protected site within the cartilage into the space between the bones in a joint. This area is called the joint cavity. This can cause pain and swelling as the sharp, hard crystals rub against soft tissue.
The process of the crystals shaking loose and leaving the cartilage is called crystal shedding.
The name of the condition comes from the substance which forms into crystals, calcium pyrophosphate.
An old name for acute CPP crystal arthritis is pseudo-gout, or false gout, because the symptoms look like a condition called gout. However, gout is caused by crystals of the waste product urate rather than calcium crystals.
It’s rare for acute CPP crystal arthritis to affect people under the age of 60.
Men and women are affected in equal numbers.
Many people with osteoarthritis, particularly of the knee, have these calcium crystals in their joint cartilage. This is called osteoarthritis with calcium pyrophosphate crystal deposition (osteoarthritis with CPPD for short).
These crystals tend to make the symptoms of osteoarthritis worse.
Symptoms of acute CPP crystal arthritis include:
- severe pain and stiffness in a joint – most commonly the knee
- the pain and stiffness comes on quickly and reaches its worst in just 12-24 hours
- swelling and tenderness of the joint
- redness of the skin over the joint
- occasionally fever – a raised temperature – causing sweating and a general feeling of being unwell.
The knee is the joint most commonly affected by this condition, but people can also get acute CPP crystal arthritis in the wrist, shoulder, ankle and occasionally other joints. Usually just one joint is affected at any one time.
These symptoms tend to last from several days to two weeks. Acute CPP crystal arthritis usually settles on its own without needing treatment.
You may notice the swelling going down within a week, though your joints may be very painful for the first few days. Affected joints may take two to three weeks to return to normal.
Chemical changes within the body that can happen as part of the ageing process, can make it more likely for calcium crystals to form.
There are conditions that can increase the amount of calcium in someone’s body. One such condition is called hyperparathyroidism. This involves the parathyroid glands in the throat being overactive. These glands control the level of calcium in the body.
A condition that leads to too much iron in the body, called haemochromatosis, can also lead to acute CPP crystal arthritis.
A rare cause of acute CPP crystal arthritis is hypomagnesaemia. This is a condition in which people don’t have enough of the mineral magnesium.
Research has found that people can inherit a faulty gene that may rarely lead to the production of too much pyrophosphate. It can also cause repeat attacks of acute CPP crystal arthritis at an unusually young age – even in the 20s or 30s.
In the cartilage of someone who has osteoarthritis, the concentration of pyrophosphate is increased, making it more likely that crystals will form.
What triggers a painful episode of acute CPP crystal arthritis?
The pain and swelling of acute CPP crystal arthritis happens when the crystals shed from cartilage into a joint. Often, it’s not clear why the crystals have shed.
Sometimes though it will be obvious what has caused the crystals to shake loose.
For example, an injury to your knee may shake the crystals loose, causing pain and swelling a day or two afterwards.
Another common trigger of crystal shedding is an illness that causes a fever, such as having the flu or a chest infection.
A major stress to your body – such as having an operation or a heart attack – can cause the crystals to shed.
Acute CPP crystal arthritis can appear very similar to both gout and an infection within the joint.
It’s very important to see your doctor when you first have symptoms of pain, swelling and redness over a joint, because they’ll need to carry out tests to rule out other conditions.
What tests are there?
There are several tests that can be carried out to help make a diagnosis of acute CPP crystal arthritis, including:
- testing your joint fluid for crystals and infection
- X-rays and ultrasound scans to show if there are any calcium crystals in the cartilage or excess fluid in the joint
- blood tests to look for:
- calcium levels
- an infection or infections
- possible problems with your kidneys.
Symptoms of acute CPP crystal arthritis usually settle on their own without any treatment. However, because they can be very painful and distressing, treatment aimed at easing pain and reducing inflammation may be offered.
Joint aspiration and injection
Your doctor may use a needle and syringe to take fluid out of your joint.
This is called aspiration, and it can quickly reduce the high pressure in the joint which is causing pain. They will numb the area with an injection first so it isn’t painful.
This procedure is fairly simple and quick, and it usually brings fast relief.
Usually, once the excess fluid has been drawn out, your doctor will inject a small amount (1–2 ml) of a long-acting steroid back into the joint through the same needle. This helps to reduce inflammation in the lining of your joint and prevent the build-up of more fluid.
Applying an ice-pack around the painful region is a quick and safe way of taking the edge off pain. You can buy ice packs, or you can use a pack of frozen peas or ice cubes wrapped up in a damp towel, to protect your skin. You can apply it for about 15-20 minutes at a time.
Non-steroidal anti-inflammatory drugs (NSAIDs)
Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, may reduce the inflammation and ease the pain.
As with any drugs there can be side effects to taking NSAIDs. Talk to your doctor if you have any concerns.
Colchicine can ease the pain and swelling of acute CPP crystal arthritis. It works by reducing the interaction between the crystals and your immune system.
To be effective, colchicine needs to be started within 24 hours of the start of the attack. The usual dose of colchicine is 0.5 mg two to four times a day.
Your doctor may decide not to prescribe colchicine if:
- you have reduced kidney function
- you’re on certain drugs, such as statins for cholesterol or certain antibiotics, that colchicine can interact with and cause side-effects.
Living with acute CPP crystal arthritis
Following an attack of inflammation it’s important that you get the affected joint and muscles moving 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. A physiotherapist can help you with expert advice.
If you have osteoarthritis with calcium pyrophosphate deposition disease, you should do regular strengthening exercises and aerobic exercises. Aerobic exercise is anything that increases your pulse rate and makes you at least a bit short of breath.
Diet and nutrition
Calcium crystal diseases aren’t usually caused by what you eat. Special diets and supplements are needed only for the very few people whose condition is caused by magnesium deficiency or kidney problems.
For general health and well-being you should eat a well-balanced diet and avoid becoming overweight. This is particularly important if you have osteoarthritis of the knee or hip.
Calcium crystal diseases can’t be caused by eating too much calcium. It’s important to have enough calcium in your diet, for example from dairy products. Otherwise you might be at risk of developing the condition osteoporosis, which causes bones to thin and fracture.