Can gout be fake? Learn more about pseudogout!

Author: Su Yin, Chief Physician, Peking University People's Hospital

Reviewer: Zhang Zhuoli, Chief Physician, Peking University First Hospital

Many people think that red, swollen, hot and painful joints are gout attacks, but in fact they may be pseudogout, which needs to be identified.

Pseudogout is a form of arthritis caused by the deposition of calcium pyrophosphate in the articular cartilage, meniscus, synovium and periarticular tissues, which causes reactive inflammation and triggers acute swelling, pain and tenderness in the joints.

Figure 1 Original copyright image, no permission to reprint

Calcium pyrophosphate is a product of abnormal metabolism in the body and is not closely related to diet. The cause of abnormal calcium pyrophosphate metabolism is still unclear and may be related to multiple factors such as gene mutation.

The incidence rate of pseudogout is not very high and is related to age. The incidence rate gradually increases with age.

1. Pseudogout VS gout

Gout is caused by deposits of monosodium urate, which can be deposited in many parts of the body. Pseudogout is caused by deposits of calcium pyrophosphate in the joints and rarely in other parts of the body.

The acute attack stage of pseudogout is very similar to gout, with local redness, swelling, heat and pain in the joints and limited movement. In the chronic stage, both can cause multiple arthritis, resulting in pain that cannot be relieved in the short term and recurring.

Pseudogout often first attacks large joints, especially the knee joints. It can be a single attack and last for 1-4 weeks before relief. Gout caused by high uric acid is more common in the first metatarsophalangeal joint of the foot. About 80% of patients have this joint as the first site of attack. The first attack will be relieved by itself within 3 days to a week.

Gout is the deposition of monosodium urate. Urate deposits cannot be seen on X-rays because urate can pass through X-rays. However, pseudogout can be seen as calcium pyrophosphate deposits on X-rays.

2. Typical manifestations of pseudogout

During an acute attack of pseudogout, the patient may experience symptoms of redness, swelling, heat, and pain in the joints. If these symptoms are particularly pronounced, attention should be paid to whether there is joint effusion. In the case of severe swelling, joint movement is limited and cannot bend normally, which is a typical manifestation of pseudogout. After entering the chronic stage, although the symptoms of redness, swelling, heat, and pain may be alleviated, there will still be persistent dull pain and swelling, accompanied by obvious local tenderness.

In addition, a characteristic of pseudogout is morning stiffness, which is a feeling of stiffness in the joints in the morning, which needs to be relieved by activities. In the long term, the disease may also lead to damage to the articular cartilage and joint deformities, which usually appear in the late stage of the disease and may sometimes be accompanied by osteoarthritis, leading to hyperplasia and erosion changes, and eventually causing the joints to present various deformities, also known as disability-like changes.

3. Diagnosis of pseudogout

To diagnose pseudogout, first of all, there are clinical manifestations, such as joint effusion. The joint effusion can be obtained and crystals of calcium pyrophosphate deposits can be found under a polarized light microscope to distinguish it from other arthritis diseases.

Patients who suffer from recurrent joint swelling and pain and are suspected of having pseudogout can take a regular X-ray, such as an X-ray of the knee joint. In the joint space, fine piles or irregular linear calcifications formed by calcium pyrophosphate deposits can be seen, which sometimes cross the joints and may be accompanied by joint contracture. At this time, pseudogout should be highly suspected.

In addition, you can also do an ultrasound examination to see calcium deposits, and you can also do a magnetic resonance imaging examination to see whether there is synovitis or inflammatory reaction.

The two simplest and most important examinations are observation of the joint fluid under a polarized light microscope and X-rays.

Treatment of pseudogout

The first step in treating pseudogout is to quickly relieve symptoms. The first choice of medicine is non-steroidal anti-inflammatory drugs, such as ibuprofen and diclofenac sodium, which are mainly used to relieve pain and eliminate local inflammation.

For more serious cases with joint effusion and mainly single joint disease, glucocorticoids are sometimes used locally, or joint fluid can be extracted and glucocorticoids can be injected locally at the same time. The anti-inflammatory effect of glucocorticoids is very strong and can quickly relieve symptoms, but they should not be used more than three times within a year to avoid adverse reactions.

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In addition, calcium pyrophosphate deposition may be related to low magnesium and calcium metabolism in the body. Long-term treatment can supplement magnesium, and drugs for treating rheumatoid arthritis and osteoarthritis are also effective.

There are literature reports that joint irrigation is also a treatment method, and it can be used to treat when there is a lot of calcium pyrophosphate deposited. However, on the other hand, irrigation may also induce the deposition of calcium pyrophosphate.

Other treatments include joint-protecting exercises and physical therapy, but care should be taken to minimize local trauma.

In the chronic stage of pseudogout, joint inflammation continues to be unrelieved, and joint function is impaired, resulting in joint deformity. Joint replacement surgery can be performed. If the cartilage is not damaged but only the synovium is damaged, synovectomy can also be performed.