As its name implies, pseudogout has many of the same symptoms as gout, including the sudden onset of severe pain, swelling, warmth, and redness in a joint.
Pseudogout most frequently affects the knee but can occur in any joint, including the ankle, wrist, shoulder, elbow, and hip. Unlike gout, however, pseudogout rarely affects the big toe.1
Pseudogout occurs when calcium pyrophosphate crystals accumulate in a joint and trigger an immune system response. Doctors often refer to pseudogout as calcium pyrophosphate deposition (CPPD) or acute calcium pyrophosphate crystal arthritis (acute CPP crystal arthritis).
The crystals that cause pseudogout are frequently found in the joints of older people, but only occasionally do the crystals trigger pseudogout episodes. In fact, one clinical study found that more than half the subjects undergoing total knee arthroplasty had evidence of calcium pyrophosphate crystal deposits in their joint tissue, and that almost none of the subjects who had the crystals were aware of them.2
Pseudogout is less common than gout and osteoarthritis, and it is often misdiagnosed as gout, osteoarthritis or rheumatoid arthritis. Thankfully, the initial treatments for these conditions are quite similar, so a misdiagnosis does not necessarily result in the wrong treatment.
What Is Pseudogout?
Doctors sometimes refer to pseudogout and gout as "crystal-induced arthropathies," which simply means they are joint diseases caused by microscopic crystals. The primary difference between these two diseases is the type of crystals that cause symptoms:
- Pseudogout is caused by calcium pyrophosphate dihydrate crystals, often referred to as calcium pyrophosphate crystals or CPP crystals.
- Gout is caused by monosodium urate crystals, often referred to as uric acid crystals.
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Experts believe calcium pyrophosphate crystals are produced in a joint's cartilage, and if the cartilage is disturbed through normal wear-and-tear, an injury or trauma, the crystals can be released into the joint fluid and other nearby soft tissue. This in turn can trigger an acute immune response resulting in a brief episode of severe pain, swelling, redness, and warmth called pseudogout or CPPD.
Researchers have known about calcium pyrophosphate crystals for decades but still do not fully understand the crystals' exact origins, or why some people who have them experience pseudogout episodes and others do not. There is also a lack of reliable studies regarding the number of people who get pseudogout , although it is known that the risk increases exponentially with age.3,4
Left untreated, an initial pseudogout episode will usually resolve itself within 5 to 14 days.3,5 Successive episodes may last longer and may affect more joints. Repeated instances of pseudogout inflammation can permanently damage joints over time. This damage is diagnosed as "secondary" osteoarthritis.
Research suggests people who have osteoarthritis are up to three times more likely to have calcium pyrophosphate crystal deposits than those who do not.6 Whether the crystals cause joint damage or are the result of joint damage - or both - has long been debated. Scientists agree more research needs to be done in this area.4,7