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(Calcium Pyrophosphate Crystal Deposition Disease; Calcium Pyrophosphate Dihydrate Crystal Deposition Disease)
Pseudogout is a disorder caused by deposits of calcium pyrophosphate dihydrate crystals in the fluid and tissues of the joints, leading to intermittent attacks of painful joint inflammation or a chronic arthritis similar to rheumatoid arthritis.
Crystals accumulate in the fluid and tissues of the 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 and sometimes injection of corticosteroids into joints.
Pseudogout usually occurs in older people and affects men and women equally.
The reason that calcium pyrophosphate dihydrate crystals form in some people is unknown. The crystals often occur in people who have the following:
A joint injury (including surgery)
Accumulations of protein in various organs and tissues (amyloidosis)
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)
An abnormally low magnesium level in the blood (hypomagnesemia)
A rare disorder that causes an abnormally low alkaline phosphatase level in the blood (hypophosphatasia)
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 and their causes and effects are not yet completely understood.
Symptoms of pseudogout vary widely. Some people have attacks of painful joint inflammation (arthritis), 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, where collections of crystals often occur in tissues near joints, people with pseudogout rarely develop hard lumps of crystals (tophi).
Doctors suspect the diagnosis of pseudogout in older people with arthritis, particularly when joints are swollen, warm, and painful. Doctors confirm the diagnosis by removing a fluid sample 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 microscope with polarized light.
Often, the inflamed joints heal without any residual problems. However, in some people, chronic arthritis and permanent joint damage can occur, with some joints so severely destroyed that they can be confused with neurogenic arthropathy (Charcot joints).
Usually, treatment can stop acute attacks and prevent new attacks but cannot reverse changes in already damaged joints. Most often, nonsteroidal anti-inflammatory drugs (NSAIDs) are used to promptly stop the pain and inflammation of acute attacks.
Colchicine (see Table: Drugs Used to Treat Gout) 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 rapidly 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.
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