[Low-grade-/high-grade-synovitis: synovitis-score as a gold standard?]

Synovectomy specimens represent important material submitted from the orthopedist to the pathologist. However, no consistent histopathological grading system for chronic synovitis has been established so far.

The three compartments of chronic synovitis (enlargement of lining cell layer, density of synovial stroma cells, leukocytic infiltrate) are graded semiquantitatively (from 0=absent to 3=strong), and the points for each compartment add up to the synovitis score: 0-1 = no synovitis, 2-4 = low-grade synovitis, 5-9 = high-grade synovitis. A total of 618 synovial specimens (resections n=559, biopsies n=59) from degenerative and inflammatory joint diseases were graded by two independent observers.

Median synovitis scores when correlated to clinical diagnoses were: 1, control; 2, osteoarthritis and post-traumatic arthritis; 3, psoriatic arthritis; 5, reactive and rheumatoid arthritis. The differences between rheumatic and non-rheumatic diseases were significant (p<0.001). The correlation between the two observers was high (p<0.001).

The proposed synovitis score enables stratification of chronic synovitis into low-grade (score 2-4) and high-grade (score >4), which is correlated to the nature of the disease (low-grade to non-rheumatic, high-grade to rheumatic), and it therefore contributes to the diagnosis of rheumatic and non-rheumatic joint diseases.