CT is especially helpful for evaluation of the thoracic spine and facet joints, which can be challenging to evaluate on radiography [49]. There is not a consistently established convention to guide the clinician on whether to image only the sacroiliac joints or both the sacroiliac joints and spine in patients with suspected axSpA. However, spinal involvement is common, and numerous studies have shown that axSpA involvement can be isolated to the spine, isolated to the sacroiliac joints, or can involve both the sacroiliac joints and spine [19,59-63]. Therefore, if CT is performed, imaging the spine in addition to the sacroiliac joints is beneficial in the setting of symptoms referable to the spine. There is no role for IV contrast in the CT evaluation of axSpA. Fluoride PET/CT Skull Base to Mid-Thigh There is not enough data to support the routine use of F-18-fluoride PET/CT in the evaluation of patients with suspected axSpA. F-18-fluoride has been shown to be a potentially useful tracer in identifying sites of osteoblastic activity in axSpA patients [64], with uptake corresponding to sites of active bone formation on histology [65]. Uptake on PET/CT has also been shown to correlate with clinical disease activity in patients with axSpA [66,67]; however, there is conflicting evidence regarding the extent to which tracer uptake correlates with specific Inflammatory Back Pain inflammatory and structural lesions seen on CT and MRI resulting in uncertainty about its diagnostic utility [64,67- 72]. In one study, the interreader reliability of diagnosing sacroiliitis on PET/CT was poor and substantially lower than that for MRI or CT [67]. In a small study using radiographs as the reference standard, F-18-fluoride PET/CT had a sensitivity of 80% and specificity of 77% for the detection of sacroiliitis in AS, although there are inherent limitations in the use of radiographs as the reference standard for diagnosing axSpA [73].
Inflammatory Back Pain Known or Suspected Axial Spondyloarthropathy PCAs. CT is especially helpful for evaluation of the thoracic spine and facet joints, which can be challenging to evaluate on radiography [49]. There is not a consistently established convention to guide the clinician on whether to image only the sacroiliac joints or both the sacroiliac joints and spine in patients with suspected axSpA. However, spinal involvement is common, and numerous studies have shown that axSpA involvement can be isolated to the spine, isolated to the sacroiliac joints, or can involve both the sacroiliac joints and spine [19,59-63]. Therefore, if CT is performed, imaging the spine in addition to the sacroiliac joints is beneficial in the setting of symptoms referable to the spine. There is no role for IV contrast in the CT evaluation of axSpA. Fluoride PET/CT Skull Base to Mid-Thigh There is not enough data to support the routine use of F-18-fluoride PET/CT in the evaluation of patients with suspected axSpA. F-18-fluoride has been shown to be a potentially useful tracer in identifying sites of osteoblastic activity in axSpA patients [64], with uptake corresponding to sites of active bone formation on histology [65]. Uptake on PET/CT has also been shown to correlate with clinical disease activity in patients with axSpA [66,67]; however, there is conflicting evidence regarding the extent to which tracer uptake correlates with specific Inflammatory Back Pain inflammatory and structural lesions seen on CT and MRI resulting in uncertainty about its diagnostic utility [64,67- 72]. In one study, the interreader reliability of diagnosing sacroiliitis on PET/CT was poor and substantially lower than that for MRI or CT [67]. In a small study using radiographs as the reference standard, F-18-fluoride PET/CT had a sensitivity of 80% and specificity of 77% for the detection of sacroiliitis in AS, although there are inherent limitations in the use of radiographs as the reference standard for diagnosing axSpA [73].