P. 322

An Urban Experience
A.R. Alleman1
1Lighthouse Veterinary Consultants, LLC, Gainesville, FL 32606
Synovial  uid 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  uid analysis is to classify the  uid as nonin ammatory or in ammatory during the microscopic exam, a fast and simple anaysisi can be performed on a small volume of  uid (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  ndings. Those joints that are obviously effusive should be sampled. However, in dogs and cats, even if only one joint appears clinically affected,  uid should be collected from multiple joints in order to document a polyarthropathy. The carpi and sti es are most frequently sampled.
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  uid will form at least a 1 inch long string before the strand is broken. Microscopically, normal synovial  uid has a very dense granular eosinophilic background as illustrated in the  gure.
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  eld) 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  uid on a 100 X oil objective, if the  uid 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  elds. In the cat, there should be less than 1 nucleated cell seen in 10 microscopic  elds.
Differential Cell Count: Normal synovial  uid 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  uid during the collection process will cause the addition of increased number of nucleated cells, mostly neutrophils, sometimes making an interpretation of in ammatory vs. Nonin ammatory joint disease dif cult.
Nonin ammatory Joint Disease: In patients with nonin ammatory 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  elds). 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 nonin ammatory disease: Degenerative joint disease, Trauma, Hemarthrosis, and Neoplasia.
In ammatory Joint Disease: The cardinal features
of most in ammatory 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  eld. 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 in ammatory
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  uid will still be classi ed as in amed if an increased number of neutrophils are present. Occassionally, an in ammatory 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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