Pseudogout (acute CPP crystal arthritis): treatment, symptoms and causes

Arthritis UK explains that calcium crystals occur naturally in the body and help to make our teeth and bones strong. Some people have these crystals in other places, such as the cartilage that covers the ends of the bones in a joint. Many people have crystals in their cartilage for years without any problems. But sometimes the crystals shake loose (this is called shedding) and move into the joint cavity, where the hard, sharp crystals rub against softer tissues and cause painful inflammation and swelling.

This is acute calcium pyrophosphate (CPP) crystal arthritis, formerly called pseudogout. "Acute" means the symptoms develop quite suddenly. Patient.info describes the wider group of problems as CPP deposition (CPPD), which includes acute attacks and a longer-term condition called chronic CPP crystal inflammatory arthritis. Crystals on cartilage that cause no symptoms are called chondrocalcinosis and may only be picked up on an X-ray.

Arthritis UK says symptoms usually settle on their own after a time, but because an attack can be very painful you can get treatment to ease the pain and reduce inflammation. Patient.info says pseudogout cannot be cured, but treatment is available to relieve the symptoms until the attack settles.

Arthritis UK lists the symptoms of an acute attack. Usually just one joint is affected at a time.

• Severe pain and stiffness in a joint that comes on quickly and reaches its worst in just 12 to 24 hours.

• Swelling and tenderness of the joint.

• Redness of the skin over the joint.

• Occasionally a fever, with sweating and a general feeling of being unwell.

Patient.info says it is always a problem sorting out pseudogout from gout, as they can cause identical symptoms, and the difference becomes apparent only when tests show the problem is CPP crystals rather than uric acid crystals. Unlike gout, pseudogout cannot be diagnosed on a blood test alone.

Arthritis UK says several factors increase the risk of crystals forming.

• Age. Chemical changes as we get older make it more likely that calcium crystals will form. Patient.info says CPPD becomes more common with age.

• An overactive parathyroid gland (hyperparathyroidism).

• Too much iron in the body (haemochromatosis).

• More rarely, a lack of magnesium (hypomagnesaemia).

• Osteoarthritis, which increases the concentration of calcium pyrophosphate in the joint.

• Rarely, an inherited faulty gene.

Often it is not clear why crystals have shed. Arthritis UK says an injury to the knee may shake the crystals loose, causing pain and swelling a day or two afterwards. An illness that causes a fever, such as flu or a chest infection, or a major stress to the body, such as an operation or a heart attack, may also trigger shedding.

Patient.info lists further triggers, including dehydration, any severe illness, long-term steroid medicine, an underactive thyroid, kidney dialysis, surgery or injury and low magnesium. It suggests keeping your fluid intake up, since dehydration is a trigger.

Arthritis UK says it can be difficult to diagnose because the crystals may be small and difficult to find, and the symptoms may be very similar to other conditions such as gout or a joint infection. You should see your doctor when you first have pain, swelling and redness over a joint. They will examine your joints, ask about your symptoms, and carry out tests to help with diagnosis and to rule out other conditions or infection.

• Testing joint fluid, taken with a needle and syringe, for crystals or signs of infection.

• X-rays and ultrasound scans, which can show calcium crystals in the cartilage, excess fluid or joint damage.

• Blood tests for inflammation, minerals such as calcium, magnesium and iron, infection and kidney problems.

Arthritis UK says symptoms tend to last from several days to two weeks. The joint may be very painful for the first few days. Swelling may go down within a week, though it may take 2 to 3 weeks for the joint to get back to normal. Patient.info says attacks usually settle in about ten days.

Attacks can recur. Patient.info says colchicine can be used as a preventative treatment for people who have frequent attacks, and that treating an underlying cause such as dehydration or low magnesium may prevent further attacks.

A sudden hot, red, swollen joint should be assessed promptly, because the symptoms can be very similar to a joint infection (septic arthritis), as Arthritis UK points out. See a GP or call NHS 111 the same day, particularly if you also have a fever or feel generally unwell, and go to A&E if you cannot get prompt advice or the joint is rapidly worsening.

Arthritis UK suggests keeping active once a flare-up is under control, as exercise can strengthen the muscles and improve pain and fatigue. It says calcium crystal diseases are not caused by eating too much calcium, and that you need enough calcium in your diet to avoid osteoporosis, so a well-balanced diet is recommended. Patient.info says the damage from chronic CPP crystal arthritis can be limited by keeping your weight normal and getting moderate exercise.

On the NHS, a GP can examine the joint, arrange tests and prescribe treatment, and may refer you to a rheumatologist or orthopaedic team if the diagnosis is unclear or attacks keep recurring. Some people choose private rheumatology for faster access to joint aspiration and imaging. The treatments are the same in both settings.