Pseudogout

Pseudogout (calcium pyrophosphate dihydrate crystal deposition disease) is a disorder caused by deposits of calcium pyrophosphate crystals in the cartilage and then in the fluid of the joints, leading to intermittent attacks of painful joint inflammation.

Pseudogout usually occurs in older people and affects men and women equally.

Causes and Symptoms

The reason that calcium pyrophosphate crystals deposit in the joints of some people is unknown. It may occur in people who have other diseases, such as an abnormally high calcium level in the blood caused by a high level of parathyroid hormone (hyperparathyroidism), an abnormally high iron level in the tissues (hemochromatosis), or an abnormally low magnesium level in the blood (hypomagnesemia). However, most people with pseudogout have none of these conditions. The disorder can be hereditary.

Symptoms vary widely. Some people have attacks of painful joint inflammation, 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 doctors may confuse with rheumatoid arthritis. Acute attacks are usually less severe than those of gout, but as in gout, attacks in pseudogout 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, people with pseudogout do not develop tophi.

Diagnosis

Doctors make the diagnosis by taking fluid from an inflamed joint through a needle (joint aspiration). Calcium pyrophosphate crystals (rather than urate crystals) are found in the joint fluid. They can be distinguished from urate crystals using a polar light microscope. Masses of calcium pyrophosphate crystals, unlike urate crystals, are radiopaque and can therefore be seen on x-ray.

Prognosis and Treatment

Often, the inflamed joints heal without any residual problems, but in many people, permanent joint damage can occur, with some joints so severely destroyed that they can be confused with Charcot's joints (see Section 6, Chapter 95).

Usually, treatment can stop acute attacks and prevent new attacks but cannot prevent damage to the affected joints. Most often, nonsteroidal anti-inflammatory drugs (NSAIDs), including the COX-2 inhibitors (coxibs), are used to reduce the pain and inflammation (see Section 6, Chapter 78). Occasionally, colchicine may be given intravenously to relieve the inflammation and pain during attacks and can be given by mouth in low doses daily to prevent attacks. Sometimes, excess joint fluid is drained and a corticosteroid suspension is injected into the joint to reduce the inflammation. No effective long-term treatment is available; however, physical therapy (such as muscle-strengthening and range-of-motion exercises) may be helpful.