Pseudogout (CPPD)

What Is It?

Pseudogout is a form of arthritis triggered by deposits of calcium crystals (calcium pyrophosphate dehydrate) in the joints. It is also called calcium pyrophosphate deposition disease (CPPD). This disease can cause short-term or long-term joint swelling, most frequently in the knee, wrist, shoulder, ankle, elbow or hand. As the name suggests, this condition can appear similar to gout, another arthritic condition caused by another type of crystal that commonly causes the sudden pain and swelling in a single joint. However, gout is caused by uric-acid crystals, and gout tends to occur in the big toe or midfoot. Pseudogout also can resemble osteoarthritis or rheumatoid arthritis.

Pseudogout most commonly affects the elderly. It occurs in about 3 percent of people in their 60s and as many as half of people in their 90s. The cause is unknown. Because many people affected by this disease already have joint damage from other conditions, it is probable that the physical and chemical changes of aging make them more susceptible to crystal formation. One theory is that an injury to cartilage allows calcium crystals to be released into the joint space, and these crystals trigger an inflammatory response.

In some cases, other medical conditions can make people more susceptible to pseudogout. These include an underactive thyroid (hypothyroidism), a genetic disorder of iron overload (hemochromatosis) or excessive blood levels of calcium (hypercalcemia). Pseudogout also can be triggered by joint injury, such as joint surgery or a sprain or the stress of a medical illness. Frequently, however, nothing can be identified that might have triggered the disease.

Symptoms

Symptoms include:

• Pain, swelling and stiffness around a single joint, especially the knee. Occasionally, more then one joint is affected at the same time.
• Fever, usually low-grade

Diagnosis

Diagnosing pseudogout can be tricky because it can resemble gout, infection or other causes of joint inflammation. Also, pseudogout commonly is associated with other joint problems. Therefore, it is important that even when pseudogout is identified, other causes of joint trouble also are considered.

X-rays may reveal calcium deposits along the affected joints, although many healthy elderly people have similar findings on X-rays without the inflammation of pseudogout. Because a joint infection or other joint disease can cause similar symptoms and findings, doctors often will recommend that joint fluid be removed from an inflamed joint and analyzed for CPPD crystals, as well as for evidence of gout crystals, inflammation or infection. Your doctor also may want to do tests for other conditions that can trigger pseudogout. These may include tests of iron, calcium and thyroid function.