Pseudogout (Calcium Pyrophosphate Deposition Disease)

What pseudogout is

Calcium pyrophosphate crystals form in joint cartilage, particularly the shock-absorbing menisci of the knee and the cartilage of the wrist. Their buildup is called chondrocalcinosis, which shows as fine white lines on X-ray. Many older people have these deposits without any symptoms.

When crystals break loose into the joint space, the immune system attacks them as if they were germs. The resulting inflammation causes a sudden, painful flare. This acute attack is pseudogout. The name reflects how closely it mimics gout, which is caused by uric acid (urate) crystals instead.

Forms of CPPD disease

Symptoms

• sudden pain, swelling, warmth and redness in a joint, building over 6 to 24 hours
• the knee is affected in about half of attacks; wrists, shoulders, ankles, elbows and hips are next most common
• usually one joint, sometimes several
• stiffness and difficulty using the joint
• low-grade fever and feeling unwell, especially in older adults, sometimes with confusion
• a tense, fluid-filled joint (effusion)

Attacks often follow a trigger such as surgery (especially parathyroid surgery), a serious illness, a stroke or heart attack, an injury to the joint, or a joint injection.

Pseudogout vs gout

Gout and pseudogout can occur together, which is one reason joint fluid testing matters.

Causes and risk factors

• Age: the main risk factor. Chondrocalcinosis is found in a large minority of people over 80.
• Previous joint injury or surgery, and osteoarthritis.
• Metabolic conditions, especially in people under about 55: - hyperparathyroidism (high calcium) - hemochromatosis (iron overload) - hypomagnesemia (low magnesium), including from long-term proton pump inhibitor use - hypophosphatasia, a rare bone disorder
• Family history: rare inherited forms start early in life.
• Some medicines, including loop diuretics.

How pseudogout is diagnosed

1. Joint aspiration (arthrocentesis): the doctor uses a needle to draw fluid from the swollen joint. Under a polarized light microscope, CPP crystals confirm the diagnosis. The fluid is also sent for Gram stain and culture to rule out septic arthritis, which can coexist with crystals. Draining the fluid also eases pain.
2. X-ray: may show chondrocalcinosis in the knee menisci, wrist or pubic joint.
3. Ultrasound: can detect crystal deposits in cartilage more sensitively than X-ray.
4. Blood tests: inflammation markers, and in younger people or recurrent cases, calcium, magnesium, phosphate, iron studies, parathyroid hormone and thyroid function, to look for an underlying cause.

Treatment

During an attack

• Joint drainage plus a steroid injection into the joint: often the quickest and most effective treatment for one or two joints, once infection has been ruled out.
• NSAIDs such as naproxen or ibuprofen, if safe for you. Older adults often cannot take them because of kidney, stomach or heart risks.
• Colchicine in low doses, started early in the attack.
• Oral steroids for several joints or when other drugs are unsuitable.
• Rest, ice packs and raising the joint.

Preventing further attacks

There is no medicine that dissolves CPP crystals, unlike gout. Options include:

• treating any underlying cause, such as correcting low magnesium or overactive parathyroid glands
• low-dose daily colchicine for frequent attacks
• low-dose NSAIDs, if suitable
• for chronic inflammatory CPPD, hydroxychloroquine, methotrexate or, in difficult cases, biologic drugs such as anakinra, under a rheumatologist's care

Outlook

Individual attacks resolve, usually within 1 to 2 weeks with treatment. Some people have a single attack; others have recurrent flares or develop chronic arthritis. Over time CPPD can contribute to joint damage similar to osteoarthritis, and joint replacement is an option for severely damaged knees or hips.

Frequently asked questions

What is the difference between gout and pseudogout?

Both cause sudden, painful, swollen joints, but gout is caused by uric acid crystals, often in the big toe, while pseudogout is caused by calcium pyrophosphate crystals, often in the knee or wrist of older adults. Joint fluid examined under a microscope tells them apart. Gout has long-term uric acid-lowering treatment; pseudogout does not.

What triggers a pseudogout attack?

Attacks often follow surgery, a major illness such as pneumonia, stroke or heart attack, a joint injury, or a sudden change in calcium levels, for example after parathyroid surgery. Many attacks occur without any clear trigger. Diet does not appear to play a role, unlike gout.

How long does pseudogout last?

An untreated attack can last from a few days to several weeks. With treatment, such as draining the joint and injecting a steroid or taking anti-inflammatory medicines, most attacks settle within 1 to 2 weeks. Some people go on to have repeated attacks or chronic joint symptoms.

Can diet cause pseudogout?

No. Unlike gout, pseudogout is not linked to eating red meat, seafood or drinking alcohol, and calcium in the diet does not cause the crystals. Correcting low magnesium may help some people, and underlying conditions like hemochromatosis need medical treatment.

Can pseudogout be cured?

The crystals cannot currently be removed or dissolved, so CPPD cannot be cured. However, attacks can be treated effectively, and frequent flares can often be prevented with low-dose colchicine or other medicines. Treating an underlying metabolic cause may reduce further crystal formation.