Original articlePrevalence of calcium pyrophosphate and monosodium urate crystals in synovial fluid of patients with previously diagnosed joint diseases
Introduction
Synovial fluid (SF) analysis is one of the most useful laboratory procedures for the diagnosis of joint diseases [1], [2]. This analysis is recommended in all SF samples obtained from undiagnosed inflamed joints and it is mandatory in the suspect of septic or crystal induced arthritis [3].
Monosodium urate (MSU) and calcium pyrophosphate (CPP) crystal identification in SF allows the immediate diagnosis of gout and CPP related arthropaties, respectively. Furthermore, they may be found in joint diseases with a previous established diagnosis, providing matter for a possible associated or coexisting disease. Sometimes, the presence of CPP crystals, although insufficient to fit the diagnosis of a true CPP deposition disease [4] may be able to influence the local inflammatory reaction.
However, very few data are available on the prevalence of MSU and CPP crystals in some relevant joint diseases, such as rheumatoid arthritis (RA), spondyloarthropathy (SpA) including psoriatic arthritis (PsA) or reactive arthritis (ReA), and septic arthritis (SeA).
In this study, we report the frequency of MSU and CPP crystals in SF obtained from patients with previously diagnosed joint diseases, by evaluating retrospectively the results of 10 years of SF analysis performed in our Rheumatology Unit.
Section snippets
Methods
The study was retrospective. We reviewed the results of SF analysis of 5020 samples collected from outpatients undergoing arthrocentesis for non-traumatic joint effusions presenting at the rheumatology unit of the University of Padova between January 2000 and December 2010 and identified those with a definite diagnosis made by a rheumatologist and based on clinical examination and radiographic findings.
When more than one SF analysis data was found for the same patients, only the first was
Results
As depicted in Fig. 1, out of the 5020 SF examined, 2049 were excluded from the study due to doubtful diagnosis or missing data for diagnosis while 601 were excluded as they came from the same patient.
Table 1 shows the total number of SF analysis considered with subject characteristics subdivided according to the type of disease.
The table reports the frequency of SF crystals in OA, RA, PsA, ReA, non PsA non ReA SpA, gout, acute CPP crystal arthritis (CPP-CA), SeA, and juvenile idiopathic
Discussion
Our study shows the prevalence of CPP and MSU crystals in SF obtained from patients with previously diagnosed joint diseases. The main aim of this study was to investigate the coexistence or the association between CPP and MSU crystals with other well established joint diseases.
With the obvious exception of gout, in which they were found in the 97.7% of cases, MSU crystals were rarely observed in SFs. In this context, the disease in which MSU crystals were most frequently identified was the PsA
Disclosure of interest
The authors declare that they have no conflict of interest concerning this article.
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