Utility of 99mTc-MDP Bone Scan in Comparison to Mri and Plain Radiographs for the Diagnosis of Early Spondyloarthropathy

Abstract

Introduction: Spondyloarthropathy as a cause of inflammatory lower back ache often goes undiagnosed for long. Though various clinical criteria have been developed, evidence of sacroiliitis is considered the basis for diagnosis. As sacroiliitis may become apparent on plain radiographs after a long duration, it is important to evaluate the efficacy of other imaging techniques to make an early diagnosis. Magnetic resonance imaging (MRI) and development of various specific sequences have helped in picking up structural changes as well as inflammation in sacroiliitis. The present study is to assess the role of MRI and radionuclide bone scan in patients with early SpA of less than 3 years. Materials and methods: Patients with inflammatory LBA, defined according to the Calin criteria and satisfying the European Spondyloarthropathy Study Group (ESSG) criteria for SpA of less than 3 years duration, were included. Controls had mechanical LBA. A detailed clinical assessment and assessment of disease activity and functional impairment was done with validated measures. Radiological assessment included conventional radiograph of the pelvis, radionuclide scan and MRI of sacroiliac joints (SI joints). The sensitivity, specificity and predictive value of each modality in contributing to the diagnosis of SpA were assessed. Results: Assessment of 136 SI joints in 42 patients [(Age 29 (± 5.6) and 26 controls (Age 32.1 (± 8.91)] was done. The mean disease duration of cases was 12.5 (± 10.2) months. Conventional radiograph failed to pick up sacroiliitis in any of the cases. Positive bone scan was present in 34 cases (28 bilateral sacroiliitis, 6 unilateral sacroiliitis). Bone scan had a sensitivity of 81.8% and a specificity of 87%. Magnetic resonance imaging abnormality was present in 37/42 (88%) (bilateral in 27 and unilateral in 10) and in none of the controls. This accounted for a sensitivity of 87% and a specificity of 100%. The MRI changes included bone marrow edema (82%), synovial enhancement (60%), subchondral edema (42%), erosions (46%) and sclerosis (38%). JOSS