Calcium pyrophosphate dihydrate crystal deposition disease, Table 1. Some conditions associated with CPPD crystal deposition.

High probability of a true association
	Primary hyperparathyroidism
	Familial hypocalciuric hypercalcaemia
	Haemochromatosis
	Haemosiderosis
	Hypophosphatasia
	Hypomagnesaemia
	Bartter's syndrome
	Hypothyroidism
	Gout
	Neuropathic osteoarthropathy
	Amyloidosis
	Localized trauma (surgery for osteochondritis dissecans; hypermobility syndrome)
	Corticosteroid therapy (long-term)
	Ageing
Modest probability of a true association
	Hyperthyroidism
	Nephrolithiasis
	Diffuse idiopathic skeletal hyperostosis DISH
	Ochronosis
	Wilsons disease
	Haemophilic arthritis

The CPPD deposits may occur in cartilage (both hyaline and fibrocartilaginous), synovium, capsule, tendons, and ligaments. Chondrocalcinosis is most frequent in the knees, wrists, symphysis pubis, elbows and hips. Deposits in fibrocartilage appear on radiographs as thick, shaggy, irregular radiodense areas with a predilection for the central aspect of the joint cavity. Hyaline cartilage calcifications are thin and linear on radiographs; they may be seen parallel to and separated from the subjacent subchondral bone. In general, chondrocalcinosis of more than one set of joints usually indicates CPPD crystal deposition disease (as opposed to calcium hydroxyapatite crystal deposition disease).

The structural joint damage (pyrophosphate arthropathy) resembles the changes in degenerative joint disease both pathologically and radiographically; however, the pattern and distribution show distinctive features. Pyrophosphate arthropathy is most common in the knee, wrist and metacarpophalangeal joints. Usually the joints are involved bilaterally. Cartilage fibrillation, erosion partial or complete denudation, and joint space narrowing are typical findings. Thickened trabeculae and multiple cysts are found in subchondral bone. The cysts of CPPD crystal deposition disease typically are larger, more numerous, and of