Causes of changes in synovial fluid from joints

Changes in synovial fluid in arthritis and arthrosis

Symptom	Arthritis	Osteoarthritis
Number of cells	> 10,000 in 1 μl	<400 in 1 μl
Dominant type	Polynuclears,	Lymphocytes, monocytes,
Cells	Plasmocytes	Plasmocytes
Phagocytes	6-80% and above	Less than 5%
Protein Concentration	Significantly enhanced	Moderately enhanced
	(> 6 g%)	(<4 g%)

In clinical practice, the most common lesion of joints is detected in the following diseases.

Infectious arthritis is divided into gonococcal (arising from the dissemination of gonococcal infection) and non-gonococcal - most often caused by Staphylococcus aureus (70% of cases) and Streptococcus, as well as in many viral infections (especially rubella, infectious parotitis, infectious mononucleosis, hepatitis) and Lyme disease , caused by spirochaetes of Borrelia burgdorferi, transmitted by tick bites. Septic arthritis can cause fungi and mycobacteria.

Synovitis caused by crystals. The deposition of crystals in joints or periarticular tissues underlies gout, pseudogout and apatite disease. For the diagnosis of gout and pseudogout, a polarization microscopy of the precipitate obtained by centrifuging the synovial fluid is carried out. Use a polarizing microscope with a red filter. Needle crystals of urate, characteristic of gout, glow yellow (if their long axis is parallel to the axis of the compensator) and have a strong negative birefringence. They are found in both synovial fluid and neutrophils. Crystals of calcium pyrophosphate dihydrate, detected by pseudogout, have a variety of shapes (more often diamond-shaped), glow with blue light and are characterized by weak positive birefringence. Complexes containing hydroxyapatite (specific for apatite disease), as well as complexes containing basic calcium and phosphorus salts, can be detected only by electron microscopy. It should be emphasized that hyperuricemia should not be considered a specific sign of gout, and calcification of joints is a pseudogout, in any case, a study by polarization microscopy is necessary to confirm the diagnosis.

Rheumatoid arthritis. With an obvious predominance of inflammation of one joint, synovial fluid should be investigated to exclude the infectious genesis of its origin, since rheumatoid arthritis predisposes to infectious arthritis.

Spondyloarthropathies. This group includes a number of diseases that are characterized by asymmetric oligoarthritis. Investigation of synovial fluid is performed to exclude septic arthritis. Allocate the following spondyloarthropathies.

• Ankylosing spondylitis. Of the peripheral joints, the hip and shoulder are more often affected.
• Arthritis in inflammatory bowel diseases: 10-20% of patients suffering from Crohn's disease and ulcerative colitis develop joint damage, especially knee and ankle.
• Reiter's Syndrome and reactive arthritis that develop after urogenital or intestinal infections.
• Psoriatic arthritis develops in 7% of patients with psoriasis.

Systemic lupus erythematosus. Changes in articular fluid can be both non-inflammatory (arthrosis) and inflammatory (arthritis).

Osteoarthritis is a degenerative joint disease, characterized by "wear" of articular cartilage with subsequent bone growth along the edges of articular surfaces.

The most pronounced changes in the synovial fluid are found in bacterial arthritis. Externally the synovial fluid can have the form of pus; the cell content reaches 50,000-100,000 in 1 μl, of which neutrophils constitute more than 80%. Sometimes in the first 24-48 h of acute arthritis the number of cellular elements may be less than 25,000 in 1 μl.

In patients with rheumatoid arthritis, the study of synovial fluid is important for confirming the diagnosis and determining the local activity of the inflammatory process. In rheumatoid arthritis, the number of leukocytes in the synovial fluid rises to 25,000 in 1 μl due to neutrophils (25-90%), the protein content reaches 40-60 g / l. In the cytoplasm of leukocytes, inclusions, vacuoles, similar to a brush of grapes (ragocytes) are found. These cells contain phagocytized material - lipid or protein substances, rheumatoid factor, immune complexes, complement. Ragocytes are also found in other diseases - rheumatic, psoriatic, arthritis, systemic lupus erythematosus, bacterial arthritis, gout, but not as much as with rheumatoid arthritis.

Changes in synovial fluid in various pathological processes

Symptom	Type of change
	Non-inflammatory	Inflammatory	Septic
Colour	Straw yellow	Yellow	Varies
Transparency	Transparent	Translucent	Muddy
Leukocytes, in 1 μl	200-2000	2000-75,000	> 75,000
Neutrophils,%	<25	40-75	> 75
Crystals	No	Sometimes	No
Bacteriologic study	Negative	Negative	Sometimes positive
Diseases	Osteoarthritis, traumatic arthrosis, aseptic necrosis, systemic lupus erythematosus	Rheumatoid arthritis, gout, pseudogout, systemic lupus erythematosus, seronegative spondyloarthropathies	Gonococcal arthritis, tubercular arthritis, infectious arthritis (staphylococcus and streptococcus)

Control over the effectiveness of the treatment performed according to the results of the study of synovial fluid is indicated for infectious arthritis.

[1], [2], [3], [4], [5]