A sudden hot, swollen joint needs prompt assessment: CPPD disease, gout and a joint infection can look alike, and symptoms alone may not distinguish them. A clinician may need to take a small sample of joint fluid to look for crystals and check for infection. Even finding calcium pyrophosphate crystals does not rule out a simultaneous infection.
What CPPD disease is—and what it can look like
Calcium pyrophosphate deposition disease (CPPD), often called pseudogout when it causes an acute attack, occurs when calcium pyrophosphate crystals collect in and around joints. It is not the same as gout, which involves monosodium urate crystals. CPPD becomes more common with age and can cause sudden episodes of intense pain, swelling, warmth, redness and tenderness. The knee and wrist are common sites, but other joints can be affected. Fever and raised inflammatory markers can also occur, so a fever does not by itself tell you which condition is causing the inflammation.
CPPD has more than one pattern. Some people have acute attacks; others have gradual joint symptoms or calcium deposits visible on an X-ray without an obvious attack. Those deposits are often called chondrocalcinosis. An X-ray finding alone does not prove that CPPD is causing current pain: chondrocalcinosis can be incidental, and it is not always present in people with CPPD.
Why joint-fluid testing may be needed
When a joint is newly swollen and inflamed, examination and medical history help guide the assessment, but they may not settle the diagnosis. If appropriate, a clinician can draw fluid from the joint (joint aspiration) and examine it under a microscope. CPP crystals are typically rhomboid-shaped and may show weak positive birefringence—or none—under polarized light. Gout crystals have a different appearance.
The fluid can also be assessed for infection. This matters because infection in a joint can cause serious harm and needs urgent treatment. CPP crystals in the sample confirm that crystals are present; they do not prove that infection is absent. A person can have both crystal arthritis and a joint infection at the same time, so clinicians consider the whole picture and may send fluid for additional testing.
Seek urgent medical assessment for a suddenly painful, hot or swollen joint—particularly if you have fever or chills, feel unwell, or cannot use or bear weight on the joint. Do not assume a flare is pseudogout just because you have had one before. If symptoms are severe or worsening, seek emergency care.
How pseudogout treatment differs from gout
Treatment for an acute CPPD flare aims to reduce inflammation and pain. Depending on your health and the affected joint, a clinician may consider a non-steroidal anti-inflammatory drug (NSAID), colchicine or a corticosteroid. These options are also used for gout, but that overlap does not make the conditions interchangeable. Your clinician needs to consider factors such as other illnesses and medicines when choosing an approach.
The key difference is what treatment can do to the crystals. For gout, urate-lowering medicines can reduce uric acid and help dissolve urate crystals over time. There is currently no comparable treatment that reliably removes CPP crystals or reduces their overall burden. So gout’s urate targets, urate-lowering drugs and purine-focused prevention advice should not be assumed to prevent CPPD attacks.
Can you prevent future CPPD attacks?
For people with recurrent CPPD attacks, a clinician may discuss preventive treatment such as colchicine. Evidence for longer-term CPPD treatment is limited, and some approaches are based on experience with gout rather than extensive CPPD trials. There is no established crystal-clearing treatment. This makes prevention different from gout: the aim may be to reduce attacks, not to lower a crystal-forming substance to a target level.
If you have repeated attacks or ongoing joint symptoms, ask your clinician whether the diagnosis is confirmed and whether further assessment is appropriate. Tell them about other conditions and medicines before discussing treatment. For a new or unusually severe hot, swollen joint, arrange urgent assessment rather than treating it as a familiar flare at home.
