Calcium Pyrophosphate Deposition: Terminology and Classification

An expert panel put together by the European League Against Rheumatism (EULAR) has come up with consensus definitions for the spectrum of conditions associated with calcium pyrophosphate crystals.

They define calcium pyrophosphate deposition (CPPD) as an umbrella term for all instances of calcium pyrophosphate crystal occurrence. Chondrocalcinosis is defined as cartilage calcification and stress that it is not always due to calcium pyrophosphate deposition. Radiograogic chondrocalcinosis is neither sensitive nor specific for diagnosis of calcium pyrophosphate deposition.

Four clinical presentations can be associated with calcium pyrophosphate deposition:

• Asymptomatic CPPD: May be isolated chondrocalcinosis or associated with osteoarthritis. Often an incidental finding during imaging for another indication.
• Osteoarthritis with CPPD: CPPD in a joint that also shows changes of osteoarthritis. The knees are typically involved, although the distribution may be atypical for osteoarthritis elsewhere (e.g., radiocarpal or midcarpal, glenohumeral, hindfoot or midfoot). Cyst and osteophyte formation tends to be more prominent than in osteoarthritis without CPPD. Patients may have chronic symptoms and/or acute attacks of crystal-induced inflammation. In contrast to osteoarthritis without CPPD, there may be more inflammatory symptoms and signs.
• Acute CPP crystal arthritis: Acute-onset, self-limiting synovitis with CPPD (formerly known as pseudogout). Patients typically present with severe, rapid-onset joint pain, tenderness, swelling, and overlying erythema. The symptoms peak within 6–24 hours. May coexist with a septic joint.
• Chronic CPP crystal inflammatory arthritis: Chronic inflammatory oligoarthritis or polyarthritis associated with CPPD. Patients have occasional systemic upset with elevation of CRP and ESR and superimposed flares with characteristics of crystal inflammation (see above). Differential considerations include rheumatoid arthritis and other chronic inflammatory joint diseases in older adults.

Imaging findings are similar to those of osteoarthritis, but the dirstribution within the joint is different, with CPPD affecting non-weight-bearing surfaces of joints. It is also usually bilateral and symmetric. Synovial inflammation and joint effusions can also be seen. Osteophytes and osteochondral bodies are commonly present. Subchondral cysts are more prominent than in osteoarthritis, and may form before cartilage loss is radiographically evident. Risk factors for calcium pyrophosphate arthropathy are aging, osteoarthritis, previous joint trauma, metabolic diseases (e.g., the four Hs: hemochromatosis, primary hyperparathyroidism, hypophosphatasia, hypomagnesemia), and hereditary predisposition.

References

• Steinbach LS, Resnick D. Calcium pyrophosphate dihydrate crystal deposition disease revisited. Radiology. 1996 Jul;200(1):1-9.
• Zhang W, Doherty M, Bardin T, Barskova V, Guerne PA, Jansen TL, Leeb BF, Perez-Ruiz F, Pimentao J, Punzi L, Richette P, Sivera F, Uhlig T, Watt I, Pascual E. European League Against Rheumatism recommendations for calcium pyrophosphate deposition. Part I: terminology and diagnosis. Ann Rheum Dis. 2011 Apr;70(4):563-70.