CPPD and Other Microcrystalline Disorders

Abstract

• CPPD is a clinically heterogeneous disorder characterized by the presence of intra-articular calcium pyrophosphate (CPP) crystals that form in normally unmineralized pericellular matrix of articular hyaline and fibrocartilage. • The most common sites of involvement are the knee menisci, the triangular fibrocartilage of the wrist, and the glenohumeral joint. Chondrocalcinosis is common in these sites as well as in others (e.g., the symphysis pubis). • CPP crystals deposit primarily in the middle zone of hyaline articular cartilage in joints. In gout, by contrast, the monosodium urate crystals tend to deposit on articular cartilage surface. The differing locations of crystal deposition in these conditions result in imaging appearances – e.g., on ultrasound – that are quite distinct. • Ultrasonography has greater sensitivity than plain radiography in detecting CPPD. • Pathologic cartilage calcification in CPPD is promoted by changes in inorganic pyrophosphate (PPi) metabolism and transport, and in chondrocyte differentiation. • CPPD has a close, complex relationship with osteoarthritis, another disease that is highly prevalent in aging and increases progressively with more advanced aging. • CPPD can occur in patients younger than age 55, who have a familial variant of the condition, a history of joint trauma, or who are afflicted with certain metabolic diseases that predispose to CPP crystal deposition. • No specific evidence-based therapies exist to limit or reverse CPP crystal deposition. The inflammation promoted by CPPD crystal deposition can be managed successfully in most patients through systemic therapies typically employed for the treatment of gout. However, the evidence base for the success of such systemic therapies in resolving acute inflammatory arthritis flares in CPPD is limited compared to gout, and intra-articular glucocorticoid injection remains a mainstay of management.