Pseudogout and Calcium Pyrophosphate Deposition Disease

What is pseudogout?

Pseudogout is a joint condition where calcium pyrophosphate dihydrate crystals are deposited in and around the joints. It is known as pseudogout because it is similar to the more common crystal-induced arthritis known as gout, where urate crystals accumulate in the joints. Comparatively, pseudogout is not as common as gout. Unlike with gout, almost any joint can be affected in pseudogout it is the joint of the big toe that is most commonly afflicted. The condition that leads to pseudogout is known as calcium pyrophosphate deposition disease (CPDD).

How common is pseudogout?

Overal calcium pyrophosphate deposition disease is fairly common among seniors. It is more likely to arise in the 50s onwards and it is estimated that half of seniors aged 85 years have the disease. However, most patients are asymptomatic so pseudogout is not a common presentation. Calcium pyrophosphate deposition disease (CPDD) is often detected with radiographic investigations or may remain undetected.

Calcium Pyrophosphate Crystal Formation

Calcium pyrophosphate crystal form from the bonding of inorganic phosphate with calcium. The inorganic phosphate is sourced from the breakdown of ATP (adenosine triphosphate), the compound that transports energy in a chemical form throughout the body. It is believe dthat for some reason, the enzymes that normally breakdown ATP become overactive in the area of the joints. Nucleoside triphosphate pyrophosphohydrolase is one of these enzymes and have found to overactive in the cartilage of patients with pseudogout. The inorganic phosphate can then bind with calcium to form calcium pyrophosphate crystals that deposit in the cartilage and the lining of the joint known as the synovium.

About Pseudogout Video

Signs and Symptoms

Calcium pyrophosphate deposition disease does not always lead to pseudogout. In fact psuedogout is just one acute presentation. Most cases are asymptomatic. Caclium pyrophosphate deposition disease (CPDD) may present in five ways  and it is therefore important to to discuss the symptoms in each presentation, and not just in pseudogout.

Asymptomatic

Asymptomatic (lanthanic) calcium pyrophosphate deposition disease does not present with any symptoms. In fact CPDD is only detected in this stage when it is noticed that the cartilage of the affected joints becomes calcified (chondrocalcinosis) as is seen on an x-ray.

Acute pseudogout

Joint symptoms involve a single joint or many joints simultaneously. The knee or wrist are most commonly affected. These joint symptoms include :

  • Pain in the joints (arthralgia)
  • Swelling of the joints
  • Warmth of the joint

The symptoms may resolve and a person may be asymptomatic until another attack recurs. In a rare presentation known as pseudoseptic syndrome there may be a fever and elevated white blood cell count (leukocytosis).

Pseudo-osteoarthritis

The joints affected in this presentation of calcium pyrophosphate deposition disease includes the knees, wrists, elbows, shoulders, spine, the joints between the first and second finger bones (proximal interphalangeal joints) and the joints between the hand bones and finger bones (metacarpophalangeal joints). The cartilage changes are similar to osteoarthritis.

Pseudorheumatoid arthritis

The metacarpophalangeal (MCP) joints and proximal interphalangeal (PIP) joints are affected on both sides at the same time similar to rheumatoid arthritis. The joints may be swollen and there may also be morning stiffness.

Pseudoneuropathic joints

This is an uncommon presentation of calcium pyrophosphate deposition disease (CPDD) and it most commonly affects the knee. Joint destruction is severe and there is diminished sensation of the affected limb. However, there is no nerve disease in pseudoneuropathic arthropathy.

Causes and Risk Factors

Pseudogout is a result of calcium pyrophosphate crystal deposition in the joints. It is believed that genetic factors contribute to the overactivity of enzymes that break down ATP and allow for inorganic phosphates thus yielded to bind with calcium to form calcium pyrophosphate disease. There is some evidence to suggest that mutations of the ANKH and COL genes may be responsible. Since the condition is mainly seen in people over the age of 50 years and in the elderly, it is believed that an interplay of both age and genetics play a role in the development of crystal pyrophosphate deposition disease (CPDD) and thus pseudogout.

Although advancing age is the single most significant risk factor for the development of CPDD and pseudogout, other risk factors have been identified including :

  • Acromegaly (deformities due to excessive growth hormone).
  • Trauma to the joint as a result of severe injury or invasive joint surgery.
  • Hypercalcemia (high blood calcium levels).
  • Hemochromatosis (iron overload).
  • Hypomagnesemia (low blood magnesium levels).
  • Hypothyroidism (underactive thyroid gland).
  • Hyperparathyroidism (overactive parathyroid gland).
  • Wilson disease (congenital copper toxicity).

The presence of these risk factors and contributing conditions may cause pseudogout in younger people although it is uncommon under the age of 50 years.

Tests and Diagnosis

There are other more common forms of joint disease that present in a similar manner to calcium pyrophosphate deposition disease. This includes osteoarthritis, rheumatoid arthritis and gout. Specific criteria have now been outlined for the diagnosis of calcium pyrophosphate deposition disease. The investigations that are utilized to diagnose CPDD and pseudogout includes :

  • X-rays are the main imaging studies used in the diagnosis of CPDD. Magnetic resonance imaging (MRI) and ultrasound scans may also be of use.
  • Arthrocentesis where fluid is extracted from the joint and then sent for further laboratory testing to identify its composition.
  • Various blood tests may be conducted to diagnose and monitor the underlying causes and risk factors. However, blood tests are not helpful for diagnosing CPDD specifically.

Pseudogout Treatment

Pseudogout can be treated and managed effectively with medication. Unlike with gout, dietary change plays no specific role in the management of pseudogout.

Medication

  • Non-steroidal anti-inflammatory drugs (NSAIDs) such as naproxen, diclofenac and  indomethacin help in reducing inflammation and easing the symptoms.
  • Steroid injections into the joint (methylprednisolone) or oral corticosteroids (prednisone) to reduce pain and inflammation in severe cases.
  • Colchicine is another anti-inflammatory drugs that is commonly used in gout and may be helpful in the treatment of pseudogout.

Surgery

There is no specific surgical procedures for pseudogout. Therapeutic arthrocentesis is a procedure where fluid is removed from the joint in order to relive pain and swelling in very acute cases of pseudogout.

References :

http://www.mayoclinic.com/health/pseudogout/DS00717

http://emedicine.medscape.com/article/330936-overview

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001458/

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