Background/Purpose: Right and Moll recognized the presence of spinal inflammation/axial disease in psoriatic arthritis (PsA) in their seminal work in 1973. The prevalence of axial disease in patients with PsA varies with disease duration. The Total Body (TB)-PET/CT with the ¹⁸F-FDG radiotracer captures glucose metabolism across the entire body, and provides standardized measures as surrogates for degree of inflammation such as SUVmax. The objective of this study was to apply high-sensitivity TB ¹⁸F-FDG PET/CT imaging to identify and characterize the spectrum of spinal inflammation in patients with PsA.

Methods: We prospectively recruited 25 PsA patients (6 female, 19 male; mean age of 51.4±16.4 years), as per CASPAR criteria. Among them, 8 patients had inflammatory low back pain (LBP). All subjects underwent a single-time point ¹⁸F-FDG TB-PET/CT using 1/5^th the standard radioisotope dose (78.2±4.9 MBq) (Abdelhafez Y,et al .J Nucl Med. 2022(10):1579-1585).

Degree of inflammation was quantified by using maximum standardized uptake value ratio corrected by the background level (rSUVmax).Qualitative changes in the joints (atlantoaxial, apophyseal, costovertebral/costotransverse, and sacroiliac) and entheses (cervical/thoracic/lumbar supra- and interspinous ligaments) were also evaluated.

Results: In one or more of the described sites PET imaging demonstrated abnormality in 21 (84%) patients. Notable changes respectively were observed in atlantoaxial (Figure 1), apophyseal, costovertebral/ costotransverse, and sacroiliac joints (Figure 2) in 15 (60%), 18 (72%), 11 (44%), and 5 (20%) patients in variable combinations.

20% patients(5/25) demonstrated sacroiliitis by PET imaging, among them the involvement was unilateral in three and bilateral but asymmetric in two patients (Figure 2). A patient with PsA with inflammatory LBP for >5 years had no evidence of sacroiliitis on MRI but demonstrated unilateral pronounced sacroiliitis on PET.

Increased ¹⁸F-FDG uptake suggestive of active inflammation on PET imaging was observed in cervical, thoracic, and lumbar spine enthuses (Figure 3) in 14 (56%), 17 (68%), and 15 (60%) patients, respectively. Overall, spinal enthesitis was evident in 80% (20/25) patients.

Quantification of the total spinal inflammatory load (rSUVmax ) could be measured in each patient, the summed rSUVmax/patient was on average 7.3±3.1 for all the described sites.

Conclusion: TB-PET/CT scan is an US FDA approved technology. We observed spinal inflammation to be a dominant pathology in PsA : i. Our findings provide direct in-vivo evidence that enthesitis could be the primary pathology for axial inflammation in PsA; spinal enthesitis was observed in 80% of patients. In majority of the patients this pathology was clinically occult, as only about one third of the patients reported back pain. ii. Non-radiographic axial disease in PsA remains unaddressed. Here we have demonstrated this condition in PsA and we provide TB-PET/CT as a biomarker tool to diagnose this condition. iii. In-vivo TB-PET imaging provided the total inflammatory burden (rSUVmax) of the whole spine thus demonstrating the ability of TB-PET/CT as a quantitative tool for assessing disease severity and for therapeutic response.

« Back to ACR Convergence 2023

ACR Meeting Abstracts - https://acrabstracts.org/abstract/spinal-inflammation-a-dominant-pathology-in-psoriatic-arthritis-characterization-and-quantification-by-in-vivo-18f-fdg-total-body-pet-ct-imaging/