[Hydroxyapatite rheumatism (multiple tendon calcification disease). II. - Microscopic study - HL-A antigen - Experimental arthritis - Pathogeny].

Optical and electron microscopic studies of the articular fluid in multiple calcification disease reveals the existence of rounded intra- and extracellular crystalline formations. These crystalline formations of calcium and phosphorus are made up of accumulations of tiny crystals shaped like fine needles 200 nm X 15-20 nm and are highly suggestive of hydroxyapatite. Crystals injected into the plantar pads of rats or the knees of rabbits induce an acute inflammatory reaction maximal at 5 hours and recovering in 24 72 hours. Hydroxyapatite crystals are swiftly dissolved in serum and more rapidly still when cells are present. Their dissolution releases calcium into the surrounding area. HLA typing of patients with multiple tendinous calcification (28 cases) or single tendinous calcification (10 cases) shows an increased frequency of HLA A2 and BW 35 in comparison with controls.