1. Biopsy sampling
- A minimum of four synovial biopsies needs to be retrieved in small joints.
- Biopsies shall be retrieved in different areas of the joint, if possible.
- If it is clinically relevant, bacteriological, fungal and mycobacteriological assessment should be performed.
- Polymerase chain reaction analysis for RNA 16S should be performed if clinically relevant, especially if empiric antibiotic course has been started.
- If it is clinically relevant, polymerase chain reaction analysis for Lyme and Whipple diseases should be performed.
2. Biopsy processing
- The biopsies should spend 24 h in formalin 4%.
- At least two biopsies should be formalin-fixed and paraffin-embedded.
3. Histological criteria
- Synovial biopsy surface should be more than 2.5 mm2.
- A lining layer should be seen.
- Morphology of the synovial tissue should be preserved.
4. Staining and immunohistochemistry (IHC)
- H&E staining should always be performed.
- CD68 staining should be performed.
- In particular clinically relevant cases, additional staining should be performed (CD3, CD20, CD138, CD31 or FVIII).
- If performed, IHC results can be given using a semi-quantitative score.
5. Biopsies interpretation and pathologist’s report
- A synovitis score should be performed, analysing: lining layer hyperplasia, inflammatory infiltrate and resident cell activation (Krenn, other).
- Synovial pathotype should be described.
- Presence or absence of lymphoid follicles within the membrane should be described.
- Analysis can be semi-quantitative or quantitative depending on the question.
- If a semi-quantitative or quantitative analysis is performed for multiple biopsies, an average score should be calculated and given for the analysis of inflammation and vascularisation.
- The pathologist should mention the presence of granulomas
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1. Biopsy sampling
- A minimum of six synovial biopsies needs to be retrieved in large joints.
- A minimum of four synovial biopsies needs to be retrieved in small joints
- Biopsies shall be retrieved in different areas of the joint, if possible.
2. Biopsy processing
- The biopsies should spend 24 h in formalin 4%*.
3. Histological criteria
- Synovial biopsy surface should be more than 2.5 mm2.
- A lining layer should be seen.
- Morphology of the synovial tissue should be preserved.
4. Staining and IHC
- H&E staining should always be performed.
- CD68 staining should be performed.
- CD3, CD19 or CD20 staining should be performed.
- Additional CD 31 or FVIII, CD4, CD8, CD138 staining might be performed depending on the question.
5. Biopsies interpretation and Pathologist’s report
- A synovitis score should be performed, analysing: lining layer hyperplasia, inflammatory infiltrate and resident cell activation (Krenn, other).
- Lining layer hyperplasia should be scored.
- Synovial pathotype should be described.
- Presence or absence of lymphoid follicles within the membrane should be described.
- Analysis can be semi-quantitative or quantitative depending on the question.
- If a semi-quantitative or quantitative analysis is performed for a single biopsy: at least three areas of the biopsy should be assessed.
6. RNA analysis
- Biopsies of one patient can be pooled for RNA extraction if needed.
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