From the Guidelines
SPECT-CT is not the primary imaging modality for evaluating sacroiliac (SI) joint pathology, and its use is generally not recommended for the diagnosis of sacroiliitis as part of axial spondyloarthritis (axSpA) 1. The most recent and highest quality study, published in 2021, recommends MRI of the sacroiliac joints as the next imaging technique of choice after radiography in the evaluation of patients with suspected axSpA 1. This is because MRI can identify both active inflammatory lesions and chronic structural lesions of the sacroiliac joints, and has been shown to be predictive of both subsequent radiographic disease progression and the likelihood of response to therapy 1. Some key points to consider when evaluating SI joint pathology include:
- Radiography is recommended as the first imaging modality for evaluation in cases of suspected axSpA, but it has a low sensitivity for detecting abnormalities in the early stages of the disease 1.
- MRI of the sacroiliac joints is the best examination for the assessment of acute inflammatory changes, and should include fat-suppressed fluid-sensitive sequences such as T2-weighted fat-saturated or STIR images 1.
- CT may be helpful in identifying subtle erosions and soft-tissue ossification, especially in patients unable to undergo MRI examination, but it lacks sensitivity for the direct inflammatory changes of early axSpA 1. Overall, while SPECT-CT may provide some diagnostic information, it is not the primary imaging modality for evaluating SI joint pathology, and its use should be guided by the clinical context and the availability of other imaging modalities.
From the Research
Role of SPECT CT in Evaluating the Sacroiliac (SI) Joint
- SPECT CT is a diagnostic modality that can be used to evaluate the SI joint, particularly in cases of sacroiliitis [(2,3,4)].
- The study by 2 found that SPECT/CT was useful in diagnosing severe SIJ dysfunction, with all 32 patients showing tracer accumulation with a standardized uptake value (SUV) of >2.2.
- Another study 3 found that SPECT scanning identified sacroiliitis in 38% of patients with inflammatory low back pain, compared to none in controls.
- The diagnostic utility of SPECT/CT has been compared to MRI, with one study 4 finding that visual scoring of SIS ratios of SPECT/CT images had high sensitivity and negative predictive value in axial spondyloarthritis, although the diagnostic utility was inferior to MRI.
Comparison with Other Imaging Modalities
- MRI is considered the modality of choice for suspected inflammatory sacroiliitis 5.
- Radiography and CT, especially low-dose CT, are reasonable alternatives when MRI is unavailable [(5,6)].
- Low-dose CT has been shown to have a lower effective radiation dose than radiography 6.
Clinical Applications
- SPECT/CT may be a suitable supplementary diagnostic modality for SIJ dysfunction 2.
- Visual scoring of SIS ratios of SPECT/CT images can be used to identify sacroiliitis in patients with axial spondyloarthritis 4.
- SPECT/CT can be used to predict the prognosis of SIJ dysfunction, with patients exhibiting higher levels of tracer accumulation requiring more advanced treatment 2.