Calcium pyrophosphate dihydrate ( CPPD) crystal deposition disease, also known as pseudogout and pyrophosphate arthropathy, is a rheumatology disease which is thought to be secondary to abnormal accumulation of calcium pyrophosphate dihydrate crystals within joint soft tissues. The knee is most commonly affected. The disease is metabolic in origin and its treatment remains symptomatic.
Signs and symptoms
- severe pain
- warmth
- swelling of one or more joints
- severe fatigue
- fever
- feeling of malaise or influenza-like symptoms
- inability to walk or perform everyday tasks or hobbies
- gnawing/chewing sensations in the joints
- burning
The symptoms can be monoarticular (involving a single joint) or polyarticular (involving several joints). Symptoms usually last for days to weeks, and often recur. Although any joint may be affected, the knees, wrists, and hips are most common.
CPPD crystals appear as shattered glass under the microscope. When released into the synovial fluid, it causes unbearable pain to the patient.
Flares are sudden, severe and without warning. Diet does not appear to cause flares. Overexertion of any exercise, standing too long, shopping, stressful or loud environments, can or may lead to severe flares, which can last from one hour to months. Although, in some patient interviews, alcohol may be a known trigger.
X-ray, CT, or other imaging usually shows accumulation of calcium within the joint cartilage, known as chondrocalcinosis. There can also be findings of osteoarthritis. The white blood cell count is often raised.
Cause
Heredity forms are rare. One genetic study found an association between CPPD and a region of chromosome 8q.
The gene ANKH is involved in crystal-related inflammatory reactions and inorganic phosphate transport.
Chrondocalcinosis may be extremely common in the population. CPPD flares may also be triggered by joint trauma from previous surgeries.
Diagnosis
Medical imaging, consisting of Radiography, CT, MRI, or ultrasound may detect chondrocalcinosis within the affected joint, indicating a substantial amount of calcium crystal deposition within the cartilage or ligaments. Ultrasound is a reliable method to diagnose CPPD. Using ultrasound, chondrocalcinosis may be depicted as echogenic foci with no acoustic shadow within the hyaline cartilageArend CF. Ultrasound of the Shoulder. Master Medical Books, 2013. Free chapter on acromioclavicular chondrocalcinosis is available at ShoulderUS.com or fibrocartilage. By x-ray, CPPD can appear similar to other diseases such as ankylosing spondylitis and gout.
Arthrocentesis, or removing synovial fluid from the affected joint, is performed to test the synovial fluid for the calcium pyrophosphate crystals that are present in CPPD. When stained with H&E stain, calcium pyrophosphate crystals appears deeply blue ("basophilic"). However, CPP crystals are much better known for their rhomboid shape and weak positive birefringence on polarized light microscopy, and this method remains the most reliable method of identifying the crystals under the microscope. However, even this method has poor sensitivity, specificity, and inter-operator agreement.
These two modalities currently define CPPD disease, but lack diagnostic accuracy. Thus, the diagnosis of CPPD disease is potentially epiphenomena.
Treatment
NSAIDs, Colchicine, and methotrexate may provide initial relief. There is currently no treatment for non-invasive removal of these crystals once they are deposited. Attempts to dissolve crystals in situ using enzymes turned up to be a "clinical failure". New, innovative methods using catalytic peptides are in development.
Epidemiology
CPPD is estimated to affect 4% to 7% of the adult populations of Europe and the United States. This topic last updated: Jul 24, 2018. Previous studies have overestimated the prevalence by simply estimating the prevalence of chondrocalcinosis, which is found in many other conditions as well.
It may cause considerable pain, but it is never fatal. Women are at a slightly higher risk than men, with an estimated ratio of occurrence of 1.4:1.
History
Terminology
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