From the Guidelines
Synovial inflammation is characterized by the presence of joint swelling, associated with pain or stiffness, and is a key feature of arthritis.
Key Features of Synovial Inflammation
- It is detected through clinical examination, and in doubtful cases, ultrasound, power Doppler, and MRI can be helpful 1
- Synovitis is a term used to describe inflammation of the synovial membrane, which is a key feature of rheumatoid arthritis 1
- The presence of inflammation seen with ultrasound or MRI can be used to predict the progression to clinical rheumatoid arthritis from undifferentiated inflammatory arthritis 1
Detection and Monitoring
- Ultrasound and MRI are superior to clinical examination in the detection of joint inflammation, and should be considered for more accurate assessment of inflammation 1
- MRI bone oedema is a strong independent predictor of subsequent radiographic progression in early rheumatoid arthritis, and should be considered for use as a prognostic indicator 1
- Imaging may be used to predict response to treatment, and to monitor disease activity 1
From the Research
Definition of Synovial Inflammation
Synovial inflammation, also known as synovitis, is a condition characterized by inflammation of the synovium, the lining of the joints. This inflammation can lead to the release of inflammatory molecules, which can mediate disease progression and worsening of clinical features 2.
Causes and Characteristics
Synovial inflammation is a crucial factor involved in the progression of osteoarthritis (OA) and a major player in pain onset 2. The activation of synovial tissue-resident cells recalls innate immunity cells from the bloodstream, creating a proinflammatory milieu that fuels and maintains a damaging condition of low-grade inflammation in the joint 2. The synovial membrane lining layer is the principal site of inflammation in rheumatoid arthritis (RA), where resident cells such as fibroblast-like synoviocytes (FLS) and synovial tissue macrophages are transformed toward overproduction of enzymes that degrade cartilage and bone and cytokines that promote immune cell infiltration 3.
Cell Types Involved
The following cell types are involved in synovial inflammation:
- Macrophages: play a key role in regulating secretion of pro-inflammatory cytokines and enzymes involved in driving the inflammatory response and joint destruction 4
- T cells: found in OA synovial tissues, although their role is largely unknown 5
- Mast cells: found in OA synovial tissues, with numbers as high as or sometimes even higher than in RA synovial tissues 5
- Fibroblast-like synoviocytes (FLS): transformed toward overproduction of enzymes that degrade cartilage and bone and cytokines that promote immune cell infiltration in RA 3
Grading of Synovial Inflammation
A histopathological grading system has been proposed to measure inflammation in synovial tissue, which includes:
- Hyperplasia/enlargement of synovial lining cell layer
- Activation of resident cells/synovial stroma
- Inflammatory infiltration This system grades the severity of synovitis from 0 to 9, with higher scores indicating more severe inflammation 6.