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CPPD: Managing a Prevalent Predicament

CPPD: Managing a Prevalent Predicament

Calcium pyrophosphate deposition disease (CPPD), which stems from the deposition of calcium pyrophosphate (CPP) crystals in articular hyaline and fibrocartilage cartilage, is a common cause of both acute and chronic arthritis in elderly patients. It will become increasingly prevalent as the population ages.

Conservative estimates judge that CPPD now affects at least 10 million Americans. However, although it was described in the early 1960s in both Europe and the US,1,2 fifty years later we know remarkably little about the pathogenesis of CPPD, have few randomized trials of therapies, and consequently have no proven management strategies. Fewer than 3000 references pertaining to CPPD appear in Ovid from 1962 through 2015, notably few of them randomized trials. (In contrast rheumatoid arthritis, which is only about 15% as prevalent as CPPD in the US, has over 100,000 citations.) 

CPPD can be a challenge to diagnose accurately, and is often overlooked in patients with a chronic polyarticular pattern of arthritis.3 (About 25% of patients thought to have typical osteoarthritis have  CPP crystals in their synovial fluid at the time of knee joint replacement.)4 The similar acute mono- or oligoarthritis known as pseudogout, in contrast, is usually not missed.

CPPD is also associated with a unique group of metabolic disorders including hemochromatosis and hyperparathyroidism. It occurs in both sporadic and familial forms.
 

Why is CPPD so poorly understood?

•   Elderly patients often have several reasons for joint pain, and sorting these out can be difficult.    
•   The lack of effective therapy may discourage a careful clinical diagnosis of CPPD.
•   CPP crystals are small, weakly birefringent, and difficult to find under polarizing light microscopy.
•   Diagnostic tests are nuanced and easy to misinterpret.
•   Perhaps most importantly, the lack of clear well-validated diagnostic criteria has hampered progress in this disease.

How do we differentiate CPPD from other common forms of arthritis? This is a critical issue for those of us caring for patients with CPPD.  

•   Acute CPPD (also known as pseudogout) often presents very much like acute gouty arthritis. It can be diagnosed by observing CPP crystals in synovial fluid from the affected joint (Figure 1).  Suspect acute CPPD when the involved joint is not typical of gout, such as a shoulder or wrist.
•   Important: Remember that the presence of synovial fluid crystals does not rule out septic arthritis.
•   The chronic polyarticular forms of CPPD are typically more challenging to diagnose. They often mimic osteoarthritis with or without inflammatory “flares” but can also present with a symmetric inflammatory arthritis resembling rheumatoid arthritis.

CPP crystals.Figure 1. The arrow points to a small cluster of CPP crystals in this micrograph of synovial fluid examined under polarizing light.

Like gout, in the absence of the ability to “crystal-prove” a patient, certain patterns of chronic arthritis suggest CPPD:  
•   a joint distribution different from that of typical OA, such as involvement of the shoulders,  wrists and 2nd and 3rd MCPs
•   characteristic radiographic features including tendon calcification and severe joint destruction.5

What are the imaging criteria for diagnosing CPPD?

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