Background Diagnosis of radiological sacroiliitis is difficult in the early stages with plain radiographs. Advanced methods such as computed tomography (CT), scintigraphy and magnetic resonance imaging (MRI) are suggested for this purpose.

Objectives To compare the role of different imaging techniques in the diagnosis of spondylarthropathy (SpA) patients with inflammatory low back pain.

Methods Thirty-four sacroiliac joints in 17 SpA patients who fulfilled the 1984 European Spondylarthropathy Classification Criteria and had inflammatory low back pain were investigated. Plain radiography, quantitative scintigraphy and MRI were performed for sacroiliac imaging. Plain radiography findings were evaluated blindly by a radiologist and rated on a 0–5 scale according to the modified New York criteria for radiological sacroiliitis. Quantitative sacroiliac scintigraphy was performed with Tc-99m hydroxy methylene diphosphonate (HMDP) and sacroiliac joint/sacrum uptake ratio for each joint was its sacroiliac index (SII). The value of SII >136 was considered as sacroiliitis. The patients also underwent MRI of sacroiliac joints with FSE T2 and SE T1 weighed images.

Results Among SpA patients the sensitivity of scintigraphy, MRI and plain radiography was 79%, 59% and 32% respectively. In 32% of 34 sacroiliac joints in which sacroiliitis was demonstrated with scintigraphy, no pathologic changes were present with MRI. On the other hand, 6% of joints were positive with MRI, but negative with scintigraphy. In cases where plain radiography showed normal radiographs, scintigraphy showed abnormalities in 44% while MRI showed abnormalities in only 18% of the joints. We couldn’t find any relationship between the sacroiliac index and plain radiography scores.

Conclusion These results suggest that the sensitivity of scintigraphy was higher than plain radiography and MRI, especially in early sacroiliitis patients with SpA.