Pseudogout (calcium pyrophosphate dihydrate crystal deposition disease) is a disorder caused by deposits of calcium pyrophosphate dihydrate crystals in the cartilage and then in the fluid of the joints, leading to intermittent attacks of painful joint inflammation.

• Crystals accumulate in joints and cause varying degrees of inflammation and tissue damage.
• The diagnosis is confirmed by finding calcium pyrophosphate crystals in joint fluid.
• Treatment is with nonsteroidal anti-inflammatory drugs (NSAIDs) and sometimes injection of corticosteroids into joints.

Pseudogout usually occurs in older people and affects men and women equally.

Causes

The reason that calcium pyrophosphate dihydrate crystals deposit in the joints of some people is unknown. It may occur in people who have other diseases, such as an abnormally high calcium level in the blood caused by a high level of parathyroid hormone (hyperparathyroidism), an abnormally high iron level in the tissues (hemochromatosis), or an abnormally low magnesium level in the blood (hypomagnesemia). However, most people with pseudogout have none of these conditions. The disorder can be hereditary. The calcium crystals frequently occur in joints affected by osteoarthritis (see Joint Disorders).

Symptoms

Symptoms vary widely. Some people have attacks of painful joint inflammation, usually in the knees, wrists, or other relatively large joints. Other people have lingering, chronic pain and stiffness in joints of the arms and legs, which may be similar to rheumatoid arthritis or osteoarthritis. Sudden painful (acute) attacks are usually less severe than those of gout, but as in gout, attacks in pseudogout can cause fever. Some people have no pain between attacks, and some have no pain at any time, despite large deposits of crystals. Unlike in gout, people with pseudogout do not develop hard lumps of uric acid crystals (tophi).

Diagnosis

Doctors make the diagnosis by taking fluid from an inflamed joint through a needle (joint aspiration). Calcium pyrophosphate dihydrate crystals are found in the joint fluid. They can be distinguished from uric acid crystals (which cause gout) using a special polarized light microscope. Masses of calcium pyrophosphate crystals, unlike uric acid crystals, can be seen on an x-ray.

Prognosis and Treatment

Often, the inflamed joints heal without any residual problems, but in many people, permanent joint damage can occur, with some joints so severely destroyed that they can be confused with Charcot's joints.

Usually, treatment can stop acute attacks and prevent new attacks but cannot reverse changes in already damaged joints. Most often, NSAIDs are used to reduce the pain and inflammation (see Pain: Nonsteroidal Anti-Inflammatory Drugs). Colchicine can be given by mouth in daily low doses to limit the number of attacks. Sometimes, excess joint fluid is drained and a corticosteroid suspension is injected into the joint to reduce the inflammation and pain. No specific effective long-term treatment is available; however, physical therapy (such as muscle-strengthening and range-of-motion exercises) may be helpful to maintain joint function.

Last full review/revision February 2008 by Daniel J. McCarty, MD