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An Urban Experience
WSVA7-0519
CYTOLOGY
THE RAPID EVALUATION OF SYNOVIAL FLUID: ALL YOU NEED IS A DROP!
A.R. Alleman1
1Lighthouse Veterinary Consultants, LLC, Gainesville, FL 32606
Introduction
Synovial fluid analysis typically includes a quantitative and qualitative interpretation such as volume, color, viscosity, total nucleated cell count and differential nucleated cell count. Since the primary goal of synovial fluid analysis is to classify the fluid as noninflammatory or inflammatory during the microscopic exam, a fast and simple anaysisi can be performed on a small volume of fluid (i.e., drops), if necessary. This is performed by assessing viscosity as a slide is being prepared for microscopic examination, and assessing mucin quality, nucleated cell counts
and differential interpretion during the microscopic examination.
Arthrocentesis is performed aseptically, usually under
(at least) light sedation. Selection joints to sample
may be dictated by physical exam and radiographic findings. Those joints that are obviously effusive should be sampled. However, in dogs and cats, even if only one joint appears clinically affected, fluid should be collected from multiple joints in order to document a polyarthropathy. The carpi and stifles are most frequently sampled.
Examination
Viscosity: Viscosity is easily assessed by gross evaluation, during the preparation of the microscope slide. Once a drip is placed on the microscope
slide, gently lift the tip of the syringe away from the slide. Normal synovial fluid will form at least a 1 inch long string before the strand is broken. Microscopically, normal synovial fluid has a very dense granular eosinophilic background as illustrated in the figure.
Total Nucleated Cell Counts: Once the slide is smeared and stained, the total nucleated cell count can be estimated during the microscopic examination. The estimation should be performed in an area of the
slide that has a monolayer of cell sand where a clear distinction between the nucleus and the cytoplasm
can be made. The formula for estimating cell counts microscopically is Nucleated cells/μl = (average # of nucleated cells per field) X (microscope objective power)2
Normal cell counts in the dog may range from 500 cells / μl up to 2,000 cells / μl. For cats cell counts rarely exceed 500 cells / μl. When examining the fluid on a 100 X oil objective, if the fluid has a normal cell count, in
the dog you should typically see less than 1 or at most, occasionally 2 nucleated cells after examination of 10 microscopic fields. In the cat, there should be less than 1 nucleated cell seen in 10 microscopic fields.
Differential Cell Count: Normal synovial fluid contains >90% mononuclear cells (Figure above) and <5% nondegenerate neutrophils. The mononuclear cells should consist predominantly of macrophages and possibley low numbers of small, well-differentiated lymphocytes. Occasionally, synoviocytes (clasmatocytes) may also be observed. These are round to oval cells with abundant basophilic cytoplasm and an eccentrically placed oval nucleus that has condensed chromatin pattern. The differential cell count may be affected, sometimes dramatically, by the presence of blood contamination. Peripheral blood intrduced into the fluid during the collection process will cause the addition of increased number of nucleated cells, mostly neutrophils, sometimes making an interpretation of inflammatory vs. Noninflammatory joint disease difficult.
Noninflammatory Joint Disease: In patients with noninflammatory joint disease, the nucleated cell count is either normal or mildly increased (less than 1 nucleated cell in every 2 or 3 100 X oil fields). Mononuclear cells will predominate, the majority of which will be macrophages (Figure on right). Some of the macrophages will
be moderately to markedly reactive with increased cytoplasmic vacuolation. Typically, a few neutrophils
will be present (<10%). Though, with hemorrhagic or traumatic lesions, a moderate number of neutrophils (<25%) may be. There are four differentials for noninflammatory disease: Degenerative joint disease, Trauma, Hemarthrosis, and Neoplasia.
Inflammatory Joint Disease: The cardinal features
of most inflammatory arthropathies are increased
cell counts most of which will be neutrophils. During microscopic examination there will be typically be 1
to many nucleated cells per 100 X oil field. Neutrophil percentages will be high, often approaching 90% of the cell population, but any time there is a predominance of neutrophils present, a diagnosis of inflammatory
joint disease should be made. This differential needs
to account for any peripheral blood contamination that may be present and could have increased the number of neutrophils observed. Even if the cell count is normal or mildly increased, the joint fluid will still be classified as inflamed if an increased number of neutrophils are present. Occassionally, an inflammatory arthropathy may be associated with increased lymphocyte percent (e.g., lymphoplasmacytic synovitis, late feline chronic progressive polyarthritis). There may be an association between this condition and anterior cruciate rupture in the dog.
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 42ND WORLD SMALL ANIMAL VETERINARY ASSOCIATION CONGRESS AND FECAVA 23RD EUROCONGRESS
  


































































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