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% 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.