Pyrophosphate arthropathy has been linked to diverse clinical subtypes. The two most common are: acute synovitis (pseudogout) and chronic pyrophosphate arthropathy ("pseudo-osteoarthritis"). We have conducted a study to examine whether these are overlapping syndromes.
We reviewed all synovial fluid (SF) analyses performed in our laboratory from January 1988 to May 1997 to determine if patterns of SF leukocyte counts and Alizarin red stains in patients with repeated samples suggest that some patients were prone to acute attacks and some to chronic pyrophosphate arthropathy and whether acute attacks superimposed on chronic symptoms were common. Joint x-rays were screened for osteoarthritis (OA) and chondrocalcinosis.
We identified 67 patients who had Calcium pyrophosphate dehydrate (CPPD) in their SF and had more than one SF examined (185 SF). We divided the patients into 2 groups. Group A (n=25) had at least one SF leukocyte count > than 2000 per mm(3) and group B (n=42) had SF leukocyte counts always < than 2000 per mm(3). Chondrocalcinosis detected on x-ray was more common in group A versus group B, 48% versus 19% (p<0.05, Fisher's exact test). OA was mild (grades 0-1) in 39% of group A versus 12.5% of group B patients, but the difference between groups was not significant. CPPD crystals were not detected in 13.5% SFs previously having CPPD crystals. Alizarin red staining for suspected hydroxyapatite was more often 2+ to 3+ in group B (31.6%) compared to group A (15.5%; p<0.05, Fisher's exact test).
Acute synovitis and chronic pyrophosphate arthropathy are often two distinctive syndromes with some patients never having inflammatory attacks. Acute synovitis is more common in patients with chondrocalcinosis while chronic pyrophosphate arthropathy is associated with increased alizarin red staining and a trend suggestive of increased severity of OA.