Calcium Pyrophosphate (CPP) Arthritis

The reason that CPP dihydrate crystals form in some people is unknown. The crystals often occur in people who have the following:

• A previous joint injury (including surgery)

• Gout

• Accumulations of an abnormal protein in various organs and tissues (amyloidosis)

• hyperparathyroidism)

• An abnormally high iron level in the tissues (hemochromatosis)

• An abnormally low magnesium level in the blood (hypomagnesemia)

• Certain rare disorders including hypophosphatasia, Gitelman syndrome, hypophosphatemic rickets, and familial hypocalciuric hypercalcemia

• Older age

However, many people with CPP arthritis have none of these conditions. The disorder rarely can be hereditary.

Calcium crystals can frequently occur in joints affected by osteoarthritis for unclear reasons. However, calcium deposits in a joint may not cause symptoms.

Symptoms of CPP arthritis vary widely. Some people have attacks of painful joint inflammation (arthritis) similar to gout flares, usually in the knees, wrists, or other relatively large joints. Other people have lingering, chronic pain and stiffness in joints of the arms and legs, which may be similar to rheumatoid arthritis or osteoarthritis.

Compared to gout flares, attacks from CPP arthritis vary more in intensity, tend to last longer, and are often more difficult to treat. As in gout, CPP arthritis attacks can cause fever. Some people have no pain between attacks, and some have no pain at any time, despite large deposits of crystals.

Unlike in gout, where collections of crystals often occur in tissues near joints, people with CPP arthritis rarely develop hard lumps of crystals (tophi).

• Microscopic examination of joint fluid

• Sometimes x-rays or ultrasonography

Doctors suspect CPP arthritis in older people with arthritis, particularly when joints are intermittently swollen, warm, and painful. Doctors confirm the diagnosis by removing a fluid sample from an inflamed joint through a needle (joint aspiration). CPP dihydrate crystals are found in the joint fluid. They can be distinguished from uric acid crystals (which cause gout) using a special microscope with polarized light.

X-rays may show masses of crystals in a joint's cartilage suggests the diagnosis. Ultrasonography of the joint may show crystals in joint cartilage and strongly suggests the diagnosis of CPP arthritis.

Often, the inflamed joints heal without any residual problems. However, in some people, chronic arthritis and permanent joint damage can occur over time, with some joints so severely destroyed that they can be confused with neurogenic arthropathy (Charcot joints).

Unlike gout, chronic CPP arthritis is difficult to treat because there is no therapy that effectively eliminates or reduces the amount of CPP dihydrate crystals. People who have frequent flares, especially younger people, are often evaluated for underlying diseases.

• Drainage of joint fluid and injection of a corticosteroid

• Medications to relieve pain and swelling resulting from inflammation

• Physical therapy

Treatment of acute CPP arthritis is similar to that for acute gout. Usually, treatment can stop acute attacks and prevent new attacks but cannot reverse changes in already damaged joints. Excess joint fluid can be drained and a corticosteroid can be injected into the joint to rapidly reduce the inflammation and pain.

Medications taken by mouth help treat CPP arthritis. Most often, nonsteroidal anti-inflammatory drugs (NSAIDs) are used to promptly stop the pain and inflammation of acute attacks.

Drugs Used to Treat Gout) can be given by mouth in daily low doses (usually 1 or 2 pills) to try to limit the number of flares.

Unlike for gout, no specific effective long-term treatment of CPP arthritis is available. However, physical therapy (such as muscle-strengthening and range-of-motion exercises) may be helpful to maintain joint function.