Single photon emission computed tomography in the diagnosis of inflammatory spondyloarthropathies

The role of bone scintigraphy in the evaluation of patients with inflammatory spondyloarthropathy is controversial and previous studies have reported a lack of sensitivity and specificity. The aim of our study was to determine whether single photon emission computed tomography (SPECT) scanning would enhance the clinical utility of bone scintigraphy in the detection of inflammatory axial disease, in particular sacroiliitis.

Twenty patients with definite sacroiliitis (New York criteria > 1) on plain film radiographs and 20 age matched controls were studied. Bone scintigraphy and SPECT scanning were carried out 2 h after an intravenous injection of 99mTc imidodiphosphonate (IDP). A quantitative and qualitative assessment of radiopharmaceutical uptake in the sacroiliac (SI) joints was derived from planar films and a qualitative analysis of uptake in the SI joints was derived from SPECT scans. All films were read without knowledge of patient identification.

Quantitative analysis of planar films did not identify any difference between study and control groups (p > 0.05). Qualitative assessment of planar films identified features of sacroiliitis more frequently in patients than in controls (p < 0.05) with a sensitivity of 25% and a specificity of 95%. SPECT scanning also revealed enhanced radiopharmaceutical uptake in the SI joints more frequently in patients than in controls (p < 0.001) with a sensitivity of 85% and a specificity of 90%. Increased uptake in the lumbar facet joints and costovertebral joints was identified in 3 patients. Similar abnormalities were not detected in the control group.

Our results indicate that SPECT scanning is both sensitive and specific for the detection of established sacroiliitis and may also identify inflammatory disease at other sites in the spine.