- In pseudogout, calcium pyrophosphate dihydrate (CPPD) crystals collect in the joint cartilage.
- Causes of pseudogout are unknown.
- Symptoms are similar to the painful joint inflammation of urate gout, but less severe.
- The prognosis is usually good.
This is a type of crystal disease, with deposits of calcium pyrophosphate dihydrate crystals within the joint and joint cartilage. The disease is not the same as gout, which is caused by deposits of uric acid crystals.
The term pseudogout arises from the similarity in presentation to the well-known common condition of gout. Patients present with an acute episodic inflammatory arthritis, much like that seen in gout. However, the crystals involved are different, hence the treatment is also different. The prognosis is usually good.
In pseudogout, CPPD crystals are deposited in the joint cartilage at the joint surfaces. It is a joint disease that manifests with intermittent attacks of acute joint inflammation. Degenerative arthritic changes can be severe, but are often asymptomatic. X-rays may show evidence of calcification of the joint cartilage (chondrocalcinosis).
The causes of pseudogout are unknown. There is a striking association with age, and the condition is rare under 50 years. It is often associated with other conditions like trauma, surgery, hyperparathyroidism, gout, and haemochromatosis. Thus it seems that the deposits of the CPPD crystals follow degenerative or metabolic changes in cartilage. Many elderly people have asymptomatic chondrocalcinosis on X-ray, reaching nearly 30 percent by age 85. Both sexes are affected, with a slight female preponderance.
There are two common presentations of pseudogout. The first is that of acute inflammation in a single joint (monarthritis), mimicking the classic acute attack of gout. The commonest presentation is sudden onset of severe pain, stiffness and swelling developing over a period of 6-24 hours. The knee is usually the site of involvement, followed by the wrist, shoulder, ankle and elbow. The joint is acutely inflamed, red and swollen and the patient, especially the elderly, may have a fever and be generally unwell and even confused. The acute attack usually clears within a few weeks, but may recur in another joint. Between attacks symptoms may be completely absent, or there may be low-grade symptoms similar to those of rheumatoid arthritis. These patterns can persist for life.
A more chronic form of this condition resembles rheumatoid arthritis in the elderly. Presentation is with chronic pain, stiffness and limitation of mobility in the knees, wrists, shoulders, elbows, hips and midfoot. Acute attacks may be superimposed on this chronic background of pain and inflammation.
Pseudogout may coexist with and aggravate osteoarthritis. Joint swelling occurs, as well as local heat and thickening of the lining of the joint – the synovium. Accumulation of fluid is called an effusion.
The prognosis is usually good, but severe joint damage can occur.
A small amount of joint fluid is drawn with a needle and syringe and examined under the microscope. If CPPD crystals are present, a diagnosis of pseudogout is made. Crystals may be seen free or within white blood cells. They differ from the crystals of uric acid as seen in gout. X-rays that show calcification of the joint cartilage can support the diagnosis. The X-rays of choice are the knees, wrists, hands and shoulders.
Aims of treatment are to reduce symptoms, identify and treat triggering illnesses and rapidly mobilize the patient once inflammation has settled. Elderly patients often have other coexisting conditions and local therapies are often the best. Low dose oral colchicine may be quite effective. If the joint is swollen from inflammation, it should be drained and injected with cortisone. Symptomatic therapy is also possible using anti-inflammatories (NSAIDs), or newer safer anti-inflammatory drugs known as COXIBs.
Patients with progressive large joint involvement such as the knee may benefit from joint replacement.