Investigation On The Early Diagnosis Of Ankylosing Spondylitis

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 118 cases with inflammatory low back pain / asymmetric synovitis on low limb, with 3 autopsy materials of non-spondyloarthropathy (SpA) sacroiliac joints serving as control. Pathological and clinical data were collected and analyzed.Results Among 118 cases, 37 cases were of ≥ grade Ⅱ and 81 cases were of grade 0/I CT sacroiliitis. No pathological change was noticed in the control group. Among them, pathological changes were found in 95 cases, including bone marrow inflammation, pannus formation, subchondral bony plate destruction, cartilage degeneration/erosion, synovitis, and enthesitis. The aforementioned first 4 findings were presented in 58 cases of grade 0/I CT sacroiliitis. Bone marrow was obtained in some cases of every grade of CT sacroiliitis except grade Ⅳ, and was all showed inflammation. Inflammatory cells infiltration, pannus formation and bony destruction could be seen in all specimens which subchondral bony were obtained. Frequency rate of cartilage erosion and ossification in grade 0/I CT sacroiliitis was the lowest in comparison with the other groups, being 80%, 91%, 93% and 100% respectively. 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. Synovial specimens were obtained in 2 cases of grade 0, 2 cases of grade Ⅰ, 1 case of grade Ⅱ and 1 case of grade Ⅲ CT sacroiliitis, but synovitis was only found in 1 case of grade Ⅰ, 1 case of grade Ⅱ, and 1 case of grade Ⅲ CT sacroiliitis. Enthesis were obtained in 5cases of grade 0/1, 3 cases of grade II and 2 cases of grade III CT sacroiliitis. However enthesitis was only presented in 1 cases of grade II and 1 case of grade III CT sacroiliitis. The inflammatory index of grade III CT sacroiliitis was the highest (3.1±1.3), followed by that of grade II and grade 0/1 CT sacroiliitis (2.9±0.9 and 2.8±1.4). The inflammatory index was significantly lower in cases of grade IV CT sacroiliitis (1.3±0.5) than that in the other groups(p<0.05). Among the 81 patients with uSpA, 58 patients were diagnosed as AS after SIJ pathological examination. The mean disease duration of these 58 cases (3.9±3.6 years) was significantly shorter than that in cases of grade II, grade III and grade IV CT sacroiliitis (5.8±3.2 years, 6.4±6.1 years and 12.3±5.2 years)(p<0.05).Conclusion Inflammatory changes of SIJ did exist before SIJ abnormality was detected by CT scan. 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.