A Swan

Synovial fluid concentration of five different cytokines in rheumatic diseases.

Interleukin-1 beta, interleukin-2, tumour necrosis factor alpha, and the interferons, alfa and gamma, were measured concurrently in synovial fluid samples from 68 patients with rheumatic diseases. Mean interleukin-1 beta concentrations (130.3 (SD 22) pg/ml) were higher in synovial fluids from patients with rheumatoid arthritis (RA) than in those from patients with osteoarthritis (27.8(4.5)pg/ml), while measurements in synovial fluids from patients with seronegative spondarthritis were intermediate (72.7 (32) pg/ml). Interleukin-2 and tumour necrosis factor alpha concentrations were lower in the inflammatory arthropathies (RA: 4.5 (0.6) U/ml, 0.39 (0.04) ng/ml; seronegative spondarthritis: 3.1 (0.3) U/ml, 0.33 (0.03) ng/ml respectively) than those in patients with osteoarthritis (5.2 (0.6) U/ml; 0.05 (0.04) ng/ml). Interleukin-2 and tumour necrosis factor alpha concentrations correlated in all groups (r = 0.7), as did the interferons alfa and gamma (r = 0.7). There was no relation between interleukin-1 beta and either interleukin-2 or tumour necrosis factor alpha, or between the interferons and any other cytokine. Several distinct cytokine patterns were noted. Synovial fluids from two non-arthritic subjects were also examined: interleukin-1 beta concentrations were low, but concentrations of the other cytokines were higher than those seen in most arthritic fluids.

The value of synovial fluid assays in the diagnosis of joint disease: a literature survey

Objective: To carry out a critical appraisal of the literature in an attempt to assess the current value of synovial fluid (SF) analysis in the diagnosis of joint disease. Methods: A literature search was undertaken using the Medline, Biomed, Bids, Pubmed, and Embase electronic databases using the keywords: synovial fluid (SF) analysis, SF crystals, joint sepsis, acute arthritis, and SF cell counts, cytology, biomarkers, and microbiology. Results: Publications fell into three main categories. Firstly, reports assessing the value of the three traditional assays (microbiology, white blood cell counts, and microscopy for pathogenic crystals). For these quality control evidence was found to be sparse, and tests for sensitivity, specificity, and reliability showed worrying variations. These poor standards in SF analysis may be due to lack of inclusion of some tests within routine pathology services. Secondly, claims for the usefulness of “new” assays (cytology and biochemical markers). For cytology, the supporting evidence was mainly anecdotal and there were no reports on specificity, sensitivity, and reliability. Interpretation difficulties are a major hindrance to the clinical use of biochemical assays, which remain primarily research tools. Finally, work on the diagnostic value of SF analysis in general. The appraisal confirmed that SF analysis remains of major diagnostic value in acute arthritis, where septic arthritis or crystal arthropathy is suspected, and in intercritical gout. Conclusions: Given the importance of SF tests, rationalisation of their use, together with improved quality control, should be immediate priorities. Further investigation is recommended into the contribution of SF inspection and white cell counts to diagnosis, as well as of the specificity and sensitivity of SF microbiological assays, crystal identification, and cytology.

Changes in cartilage metabolism in arthritis are reflected by altered serum and synovial fluid levels of the cartilage proteoglycan aggrecan. Implications for pathogenesis.

The metabolism of the cartilage proteoglycan aggrecan was studied in patients with osteoarthritis (OA, n = 83), rheumatoid arthritis (RA, n = 127), and in controls (n = 117) using monoclonal antibody-based radioimmunoassays for glycosaminoglycans in the serum and synovial fluid (SF) to detect epitope 846 on chondroitin sulfate (probably only on recently synthesized molecules) and a keratan sulfate (KS) epitope AN9PI, present on intact and degraded molecules. Epitope 846 levels were always elevated in SF over serum (mean 38-fold in OA and 8.6-fold in RA) being highest in OA patients with the longest disease duration and greatest loss of cartilage, and lowest in RA joints with high leucocyte counts. Serum levels were more often elevated in RA (56%) than in OA (19%) and probably reflect increased aggrecan synthesis in diseased joints. KS levels were higher in SF than in serum in 69% of patients (up to 2.3-fold); levels were inversely (OA) and directly (RA) related to SF leucocyte counts. Serum KS was reduced in both diseases and in RA was inversely related to both systemic and joint inflammation markers. SF 846 levels were inversely related to SF KS in both diseases. These epitopes may provide a measure of the balance between cartilage synthesis and degradation in these diseases.

Detection of crystals in synovial fluids by light microscopy: sensitivity and reliability.

Polarised light microscopy of synovial fluid is an established diagnostic technique widely regarded as reliable for the detection of crystals. The threshold concentration of crystals which can be detected has been investigated and the sensitivity and specificity of six observers compared. Various concentrations of laboratory manufactured crystals of monosodium urate monohydrate (MSUM), calcium pyrophosphate dihydrate (CPPD), and basic calcium phosphates (BCP) were added to the synovial fluid. The threshold for reliable identification of MSUM and CPPD was in the range of 10-100 micrograms/ml. False positives were frequent. The mean sensitivity of the six observers for MSUM was 69% and for CPPD was 82%. The mean specificity for MSUM was 97% and for CPPD was 78%. There was much discrepancy in the results of the slides stained with alizarin red S. Thus the value of alizarin red S as a screening test for BCP is questioned. In view of the variable sensitivity and specificity of different observers for MSUM and CPPD and the concentration threshold for reliable crystal identification, greater caution in the interpretation of synovial fluid analysis is advised, and recommendations for increased quality control are supported.

Identification of crystals in synovial fluid

Synovial fluids can contain a number of crystals and other particulate matter. Some of these, particularly monosodium urate monohydrate (MSUM) and calcium pyrophosphate dihydrate (CPPD) crystals, are pathogenic; others, including cholesterol and other lipid particles and the basic calcium phosphates (BCPs), including apatites, are of doubtful significance. Table 1 lists the main forms of particulate matter that have been identified in synovial fluids. View this table: Table 1 Intrinsic and extrinsic crystals and particles detected in synovial fluid In the case of MSUM and CPPD crystals it is clear that the identification of these crystals in a synovial fluid that also has a high polymorphonuclear cell count (indicative of acute inflammation) is the only certain way to diagnose an attack of gout or pseudogout respectively.1 Furthermore, this is one of the few tests that has been shown to change clinical practice in rheumatology,2 and it is apparent that the consequences of getting the diagnosis wrong can be severe.3 Therefore, accurate identification of MSUM and CPPD is important. There are a large number of techniques that can be used to identify crystals that can be found in synovial fluid, nearly all of which rely on microscopy of one sort or another because of the small size of the individual particles. They range from the very simple, like Garrod’s famous “string test”,4 to the furiously complex, such as laser microscopy or atomic force microscopy.5 6 In clinical practice we need a relatively simple, affordable technique, with a reasonable degree of sensitivity and specificity. Polarised light microscopy remains the only possibility that comes anywhere near fulfilling these needs: it is available in most hospitals and is relatively inexpensive; in addition, as MSUM and CPPD crystals …

Evidence for a causal relationship between the structure, size, and load of calcium pyrophosphate dihydrate crystals, and attacks of pseudogout.

OBJECTIVE--To investigate any relationship between the nature, size, and numbers of synovial fluid (SF) calcium pyrophosphate dihydrate (CPPD) crystals, and attacks of pseudogout. METHODS--Knee SF was aspirated from nine selected patients, first during an attack of pseudogout (acute sample) and again later when the attack had subsided (interval sample). CPPD crystals were extracted, weighed, examined by high resolution transmission electron microscopy (HRTEM), and characterised by size and crystal habit (monoclinic or triclinic). Structural analysis was carried out by x ray powder diffraction (XRD) and the proportions of monoclinic to triclinic CPPD were estimated from densitometric measurements of selected key reflections. RESULTS--The mean crystal size, by HRTEM, indicated that the crystals in the acute sample were larger than those in the interval sample. The ratio of monoclinic to triclinic CPPD, whether estimated from their morphological appearance by HRTEM, or from XRD, was greater in the acute than in the interval sample in all nine patients. The total amount of extracted mineral varied, but in every patient the concentration of CPPD per ml of fluid, and the total mineral per joint, were greater in the acute sample than in the interval sample. CONCLUSION--In this highly selected group of patients, the large numbers of CPPD crystals associated with attacks of pseudogout included a greater proportion of monoclinic crystals, and larger crystals, than those present when inflammation had subsided. A special, phlogistic population of crystals may exist, originating in different joint tissues, or cleared in a different manner, than the more common populations of smaller crystals with a greater proportion of triclinic CPPD, seen in chronic disease.

A tissue kallikrein in the synovial fluid of patients with rheumatoid arthritis.

Tissue kallikrein is an enzyme that forms the vasoactive peptide kallidin from an endogenous substrate L-kininogen. Tissue kallikrein has been identified in joint fluids and in inflammatory infiltrates within synovial membranes. It is suggested that tissue kallikrein and kinins have an important role in synovitis and joint damage. Immunoreactive tissue kallikrein and amidase activity were both measured in the synovial fluid of 24 patients with rheumatoid arthritis (RA) and 12 with osteoarthritis (OA). Active enzyme concentrations were higher in RA than in OA and correlated well with the lysosomal enzymes beta-glucuronidase and lactate dehydrogenase. Both total immunoreactive tissue kallikrein and the proenzyme values were similar in RA and OA. Tissue kallikrein was localised by immunocytochemistry to the polymorphonuclear leucocytes present in the synovial fluid and membranes of patients with RA.