Objective: To study the pathological features of sacroiliitis, aiming at improving the early diagnosis of ankylosing spondylitis (AS).
Methods: CT guided needle biopsy of sacroiliac joint (SIJ) was performed in 96 cases of spondyloarthropathy (SpA) patients with 3 autopsy materials of non-SpA sacroiliac joints serving as control. Pathological features were studied by two independent observers. Clinical data were collected and analyzed.
Results: No pathological change was noticed in the control group. Among the 96 cases of SpA, pathological changes were found in 76 cases, including bone marrow inflammation, pannus formation, subchondral bony plate destruction, cartilage degeneration/erosion, synovitis, and enthesitis. The aforementioned first 4 findings were present in 45 cases of grade 0/I CT sacroiliitis. In the synovial specimens obtained, synovitis was seen in some cases of grade I and all of >/= grade II CT sacroiliitis,while no inflammatory change was noticed in all cases of grade 0 CT sacroiliitis. Frequency rate of cartilage erosion and ossification in grade 0/I CT sacroiliitis was the lowest in comparison with the other groups. Moreover, in cases of grade 0/I CT sacroiliitis, cartilage erosion only present at the bony plate side, while the joint cavity side was not affected. The inflammatory index was significantly lower in cases of grade IV CT sacroiliitis than that in the other groups. Enthesitis only presented in some cases of >/= grade II CT sacroiliitis. Among the 65 undifferentiated spondyloarthropathy patients, 45 were diagnosed as AS after SIJ pathological examination. The mean disease duration of these 45 cases was significantly shorter than that in cases of >/= grade II CT sacroiliitis.
Conclusions: Inflammatory changes of SIJ did exist in cases of the < grade II CT sacroiliitis. Sacroiliitis probably initiated with bone marrow inflammation, followed by pannus formation, subchondral bony plate destruction, and cartilage degeneration/erosion, eventually leading to fibrosis, ossification and joint fusion. Synovitis and enthesitis were not the very early changes of sacroiliitis. Pathological examination was beneficial to the early diagnosis and differential diagnosis of ankylosing spondylitis.