birefringent crystals (positive)
This usually asymptomatic condition of the elderly is due to deposition of calcium pyrophosphate dihydrate (CPPD) crystals in large joints, most commonly the knee.
The crystals are initially deposited in the cartilage - chondrocalcinosis - where they are associated with degenerative changes. The shedding of the crystals into the joint space results in an acute synovitis and a clinical picture that is similar to that seen in gout.
This condition is more common in men (ratio of 1.5:1).
Last reviewed 07/2021