Tobias Manigold, Alexander Leichtle
Affiliation(s):
Department of Rheumatology and Immunology, Inselspital University Hospital Bern, Bern, Switzerland.
Background: crystal arthritides mainly comprise of gout and calciumpyrophosphat (CPP) Deposition Disease, known as CPPD or pseudogout. The prevalence, medical and socioeconomic impact of gouty arthritis is well recognized and estimated to affect 5% of the population in developed countries. However, while chondrocalcinosis, a non-pathogenic deposition of CPP crystals in cartilage, shows a high and increasing prevalence in persons over 60 years, the prevalence of CPP arthritis in daily practice remains unclear. We herein sought to assess the unbiased prevalences of crystal and crystal arthritides in synovial fluid (SF) samples at the largest hospital in Switzerland.
Methods: We included SF samples, obtained between 2015-2023 at the University hospital Bern (Inselspital), the largest hospital in Switzerland. Samples from all Departments were considered and analyzed, irrespectively of the indication for arthrocentesis and final diagnosis. Crystal analysis was performed by rheumatologists and specifically trained lab personnel. Crystals were assessed based according to negative (MSU) or positive (CPP) birefringence under polarized light as well as positive staining with alizarin red (BCP) under ordinary light microscopy. All results were documented in a semiquantitative manner (little, moderate, massive). In parallel, leucocyte counts including fractions of mononuclear and polynuclear were assessed in most SF samples.
Results: we analyzed 4777 samples from 3239 patients. Crystals were found in 39.2% of all samples, with CPP being detected in 59.3%, while 40.7% were positive for MSU. As for BCP 9.3% of samples stained positive for alizarin red. Cell numbers in SF were available in 2899 samples, among which 1703 (58.7%) were classified as inflammatory (>2000 cells/ul), and 1196 (41.3%) as non-inflammatory (<2000 cells/ul). Among inflammatory samples 38.5% were crystal positive, with CPP predominating with 58.4% versus 41.6% MSU, whereas 7.3% of samples stained positive for BCP crystals. Neither the mean of total leucocyte numbers nor the yields of polynuclear cells were significantly different between MSU and CPP positive samples.
Conclusion: Contrary to the general belief that gout is the most common form of crystal arthritis, our data indicate that CPP arthritis may in fact be the most common cause among multimorbid patients at a tertiary center. To our knowledge this is the largest study assessing the unbiased prevalence of crystals in in SF.