Diagnostic criteria*
I. Demonstration of CPP crystals, obtained by biopsy, necropsy or aspirated synovial fluid, by definitive means.
II. A. Identification of monoclinic or triclinic crystals showing a weakly positive, or a lack of birefringence by compensated polarized light microscopy.
B. Presence of typical calcifications on radiographs.
III. A. Acute arthritis, especially of knees or other large joints with or without concomitant hyperuricemia.
B. Chronic arthritis, especially of knee, hip, wrist, carpus, elbow, shoulder, and metacarpophalangeal joints, particularly if accompanied by acute exacerbations; the chronic arthritis shows the following features helpful in differentiating it from osteoarthritis.
1.Uncommon site for primary osteoarthritis.
2.Radiographic appearance.
3.Subchondral cyst formation.
4.Severe progressive degeneration, with subchondral bony collapse (microfractures), and fragmentation, with formation of intraarticular radiodense bodies.
5.Variable and inconstant osteophyte formation.
6.Tendon calcifications, especially of Achilles, triceps and obturator tendons.
7.Involvement of the axial skeleton with subchondral cysts of apophyseal and sacroiliac joints, multiple levels of disc calcification and vacuum phenomenon and sacroiliac vacuum phenomenon.
Categories
A. Definite – criteria I or II (A) and II (B) must be fulfilled
B. Probable – criteria IIA or IIB must be fulfilled
C. Possible – criteria IIIA or IIIB should alert the clinician to the possibility of underlying CPPD deposition

^*Rosenthal AK, Ryan LM. In Arthritis and Allied Conditions. Koopman, WJ (Ed) (14th edition). Philadelphia: Williams and Wilkins pg. 2348–71, 2001.