CPPD arthropathy is a joint condition caused by calcium pyrophosphate crystals building up in cartilage and joint tissues, triggering inflammation and, over time, structural damage. It was long called “pseudogout” because its sudden, painful flares mimic gout, but the underlying crystals and affected joints are different. CPPD becomes increasingly common with age, affecting roughly 3.7% of people in their late 50s and climbing to 17.5% of those in their early 80s.
What Happens Inside the Joint
The core problem in CPPD is an excess of a substance called inorganic pyrophosphate in the cartilage. Under normal conditions, enzymes break pyrophosphate down before it causes trouble. When that balance tips, pyrophosphate combines with calcium and forms solid crystals that embed in cartilage, tendons, and the soft tissue lining of joints.
Once those crystals are present, the immune system treats them as foreign invaders. White blood cells swarm the joint and activate an inflammatory cascade, producing swelling, heat, redness, and pain. This is the same general alarm system the body uses against infections, which is why a CPPD flare can look remarkably like a joint infection or gout attack. Crystal deposits are also strongly linked to cartilage breakdown and osteoarthritis, though researchers still aren’t sure whether the crystals cause the cartilage damage or whether damaged cartilage creates conditions that encourage crystal formation.
How CPPD Presents
CPPD doesn’t look the same in everyone. It spans a wide spectrum, from crystals sitting silently in a joint with no symptoms at all to severe, recurring inflammation.
- Asymptomatic deposits. Many people have calcium pyrophosphate crystals in their joints and never know it. These are often discovered incidentally on an X-ray taken for something else. The term “chondrocalcinosis,” which refers to calcification visible in cartilage on imaging, is sometimes used for this silent form.
- Acute flares. A sudden attack of intense joint pain, swelling, and warmth that develops over hours and typically peaks within a day or two. The knee is the most commonly affected joint, though wrists and ankles are also frequent targets. A single flare can last days to weeks. This is the presentation historically called pseudogout.
- Chronic CPPD arthropathy. Some people develop persistent, low-grade joint inflammation rather than distinct flares. This chronic form can resemble rheumatoid arthritis, with ongoing stiffness, swelling in multiple joints, and progressive joint damage. Older classification systems actually called this “pseudo-rheumatoid arthritis” because of the resemblance.
Rarely, CPPD causes severe destructive changes in a joint that mimic a condition called neuropathic arthropathy, where the joint essentially falls apart. This was historically labeled “pseudoneuropathic” CPPD.
Who Gets It and Why
Age is the single biggest risk factor. CPPD is uncommon before 50 and becomes dramatically more prevalent in each subsequent decade. A UK community study found the average age at identification was about 64.
In younger patients, CPPD often signals an underlying metabolic condition that disrupts the enzymes responsible for clearing pyrophosphate. The most recognized triggers include hyperparathyroidism (overactive parathyroid glands), hemochromatosis (iron overload), low magnesium levels, and a rare inherited condition called hypophosphatasia. Low magnesium is particularly worth knowing about because it can result from common, correctable causes: certain diuretic medications, chronic diarrhea, kidney problems, or conditions like short bowel syndrome. Magnesium serves as a helper molecule for the enzyme that breaks down pyrophosphate, so when magnesium runs low, pyrophosphate accumulates and crystals form.
There are also hereditary forms of CPPD that run in families and cause early-onset disease, sometimes appearing in people’s 30s or 40s.
How CPPD Is Diagnosed
The gold standard is pulling fluid from the inflamed joint with a needle and examining it under a polarized light microscope. CPPD crystals have a distinctive appearance: they’re rhomboid or rod-shaped, typically 1 to 20 micrometers long, and show weakly positive birefringence (meaning they glow faintly in a specific direction under polarized light). This contrasts sharply with gout crystals, which are needle-shaped and show strongly negative birefringence. The difference is clear-cut under the microscope and is what separates the two diagnoses.
That said, CPPD crystals can be tricky. Only about 20% of crystals in a fluid sample show enough birefringence to be easily spotted, and some show none at all. An experienced examiner makes a real difference in accuracy.
Imaging Options
When joint fluid can’t be obtained, imaging fills the gap. Standard X-rays can reveal chondrocalcinosis, the chalky line of calcium deposits in cartilage, but they miss crystals about 30% of the time. Ultrasound performs better, picking up crystal deposits with close to 100% sensitivity in studies comparing it against confirmed crystal-positive joint fluid. On ultrasound, CPPD typically appears as bright spots or bands within the cartilage itself, which is a useful distinction from gout, where crystal deposits tend to coat the surface of cartilage.
Dual-energy CT, a specialized scan that can color-code different materials in the body, also shows high sensitivity for detecting calcium pyrophosphate deposits, though it’s less widely available and still being refined for routine CPPD diagnosis.
How CPPD Differs From Gout
CPPD and gout are both crystal-driven joint diseases, but the crystals, the joints they favor, and the patient profiles differ. Gout is caused by uric acid crystals and most famously strikes the big toe, while CPPD favors larger joints like the knee and wrist. Gout tends to involve slightly more joints per flare (an average of about 2.2 joints versus 1.6 for CPPD in one comparative study). Gout is strongly tied to diet, alcohol, and kidney function; CPPD is primarily tied to aging and metabolic conditions.
Both can coexist in the same person, and both can trigger identical-looking flares of sudden joint swelling and pain. The only reliable way to tell them apart is microscopic crystal analysis of joint fluid.
Treatment for Acute Flares
There is no treatment that dissolves calcium pyrophosphate crystals once they’ve formed. Management focuses on controlling inflammation during flares and preventing recurrences.
For acute attacks, the first-line options are anti-inflammatory medications and colchicine, a drug that dampens the inflammatory response to crystals. Colchicine is typically given in small, frequent doses during a flare. When anti-inflammatory drugs and colchicine aren’t suitable, perhaps because of kidney problems or stomach ulcers, a short course of oral corticosteroids or a corticosteroid injection directly into the swollen joint can bring rapid relief. Joint injections are especially practical when only one or two joints are involved.
Managing Chronic CPPD
For people with ongoing or frequently recurring symptoms, European guidelines recommend daily low-dose anti-inflammatory medications or low-dose colchicine as maintenance therapy. A small study of patients taking colchicine daily for a year found 90% reported fewer flares compared to a year without it.
When those approaches aren’t enough, low-dose corticosteroids, methotrexate, or hydroxychloroquine may be considered. Treating any underlying metabolic condition is also important. If low magnesium, iron overload, or hyperparathyroidism is driving crystal formation, correcting the root cause can slow or reduce new crystal deposits.
Long-Term Joint Damage
Over years, CPPD can contribute to progressive cartilage loss and joint degeneration that looks like advanced osteoarthritis on imaging. The chronic inflammatory environment, combined with the physical presence of crystals embedded in cartilage, accelerates wear. Some people with CPPD develop joint damage severe enough to eventually warrant joint replacement, particularly in the knees. Because there’s no way to clear existing crystals, the goal of long-term management is reducing the frequency and intensity of inflammation to slow that progression.