Pseudogout is a form of arthritis triggered by deposits of calcium crystals (calcium pyrophosphate dihydrate) in the joints. It is also called calcium pyrophosphate deposition disease (CPPD). This disease can cause short-term or long-term swelling in joints, most often the knee, wrist, shoulder, ankle, or elbow.
As the name suggests, this condition can appear similar to gout, which is caused by another type of crystal – uric acid crystals – and commonly causes sudden pain and swelling in a single joint, usually in the foot. Pseudogout also can resemble osteoarthritis or rheumatoid arthritis.
Pseudogout is most common in the elderly. It affects about 3% of people in their 60s and as many as half of people in their 90s. Many people who get pseudogout already have joint damage from other conditions or they may have age-related degenerative joint disease. One theory is that an injury to cartilage allows calcium crystals to be released into the joint space, and these crystals cause inflammation.
In some cases, other medical conditions can make people more likely to develop pseudogout. These include:
An underactive thyroid (hypothyroidism)
A genetic disorder of iron overload (hemochromatosis)
Too much calcium (hypercalcemia) or too little magnesium (hypomagnesemia) in the blood.
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. Although age-related joint degeneration, prior joint damage or trauma, and these other medical conditions increase the likelihood of an attack of pseudogout, the reason some people develop this condition while others do not is unknown.