Calcium pyrophosphate. Histological characterization of crystals in pseudogout.

Deposits taken from an acetabulum and the head of a femur and known to contain crystals of calcium pyrophosphate were examined by selected histological methods for calcium after the application of a variety of solvents. Treatment with 10% ferric chloride removed all calcium salts tested, except a birefringent crystalline component in the pyrophosphate deposits. This corresponds to the previous optical and morphological descriptions of calcium pyrophosphate as found in synovial fluids. Calcium pyrophosphate stains consistently only by the fluorescent morin method.