The Significance of Calcium Phosphate Crystals in the Synovial Fluid of Arthritic Patients: The "Pseudogout Syndrome"

Abstract

Over 200 synovial fluids from 140 arthritics were examined for particulate matter by phase contrast and polarized light microscopy. Rhombic and rod-shaped crystals, 1 to 25 microns long, composed of a hydrated calcium salt of a complex phosphate closely resembling pyrophosphate were found in affected knees of 8 patients. Injection of a suspension of them into normal joints produced an acute arthritis. Fluid from 1 patient, a known gouty arthritic, contained urate crystals as well; unfortunately the non-urate crystals in this case were too few to permit definitive identification. The clinical and radiologic features of the 7 other cases were distinctive. All were elderly; there were 5 men and 2 women in the series, 5 were Negro, 2 were Caucasian. Two had chronic, 5 had acute, arthritis of the knee. A history of pain in other joints was obtained in most cases and objective involvement of the wrists was observed in 2 patients. Trauma, surgery and injection of a mercurial diuretic appeared to precipitate acute attacks. Abnormal articular calcifications were found in all cases; a calcification protruding into the joint was found in 3, large calcifications in the suprapatellar pouch, in 2, intra-articular fractures in 2, calcified menisci and articular cartilage in 2, osteochrondroma in 1, calcification of the articular disc of the distal radio-ulnar joint and cricothyroid cartilage in 1, sclerosis of the inferior aspect of the sacroiliac joint in 1 and localized calcific densities in both ears in 1. Because of the identical crystal populations, clinical and radiological similarities, it is suggested that these cases represent a disease entity, which we have termed "pseudogout". Review of the literature revealed 47 cases of an entity called "chrondrocale-cinosis" because of its'' characteristic roentgenographic appearance. On the basis of clinical and radiologic similarities, it is believed that pseudogout and this condition are one and the same. As only 2 of the 7 patients could have been diagnosed by the X-ray appearance alone, it would appear that the identification of the characteristic crystals is a more accurate definition of the disease. The condition may affect all 3 types of cartilage. It has been suggested by others that the underlying defect may be an inherited metabolic disturbance as it tends to be familial and because of a high incidence of associated metabolic disturbances.