Background/Purpose: Interstitial lung disease (ILD) in systemic sclerosis is treated by immunosuppressive drugs (e.g. cyclophosphamide), aimed at reduction of inflammatory response . Differentiation between inflamed and non-inflamed fibrotic tissue might help to develop treatment stratification, with the aim of improving the prognosis of (subgroups of) SSc-ILD patients. ¹⁸F-Fluoro-Dexoxyglucose Positron Emission Tomography (¹⁸F-FDG PET) scan might be a promising tool to detect inflamed lung areas, as formerly shown in a semi-quantitative setting.[1, 2] This study aims to investigate the potential role of ¹⁸F-FDG PET –scan for the quantitative assessment of metabolically active SSc related ILD.

Methods: ¹⁸F-FDG PET -scans of 22 patients with systemic auto-immune disease, including 9 with SSc , 9 with systemic lupus erythematosus (SLE) and 4 with primary Sjögren’s syndrome (pSS) , were retrospectively analyzed. FDG-uptake was quantitatively measured within 2cm-sized Regions of Interest (ROIs) at apical, medial and basal lung levels. A total of 22 ROI’s were drawn in each patient. SUVmean values of all ROI’s were corrected by the medial SUVmean bloodpool value. Subsequently, the average of 6 posterior basal SUVmean values was divided by the average of 6 posterior apical SUVmean values (basal/apical ratio). High Resolution Computed tomography (HRCT)-scans and Pulmonary Function Tests (PFT) were examined to confirm the diagnosis of ILD and to specify the pattern of fibrosis.

Results: Mean age of patients was 69.4 (SSc-ILD), 62.5(SSc without ILD), 38.9 (SLE) and, 49.3 (pSS). In SSc patients, the mean disease duration was 5.0 (SSc-ILD) and 4.4 (SSc without ILD) years. Diffuse cutaneous sclerosis was present in 2 SSc-ILD and 1 SSc without ILD patients, while other SSc patients were diagnosed with limited cutaneous SSc. ILD was present in 5 out of 9 SSc patients as confirmed by HRCT and PFT. ILD was active in 3 out of 5 SSc-ILD patients. Posterior basal/apical SUVmean ratios of SSc-ILD patients were significantly increased compared to SSc patients without ILD (p=0.016), and compared to SLE and pSS patients without ILD (p=0.001 and p=0.016, respectively), which is shown in Figure 1.

Conclusion: Our findings demonstrate that ¹⁸F-FDG PET is potentially useful for the quantitative assessment of active ILD lesions in SSc patients. The technique may therefore provide opportunities to select the patients with inflammatory regions in ILD that are most likely to respond to immunosuppression.

References:

1. Uehara, T., et al., Deep-inspiration breath-hold 18F-FDG-PET/CT is useful for assessment of connective tissue disease associated interstitial pneumonia. Mod Rheumatol, 2016. 26(1): p. 121-7.

2. Jacquelin, V., et al., FDG-PET/CT in the prediction of pulmonary function improvement in nonspecific interstitial pneumonia. A Pilot Study. Eur J Radiol, 2016. 85(12): p. 2200-2205.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-use-of-positron-emission-tomography-pet-scan-for-the-quantitative-assessment-of-interstitial-lung-disease-in-systemic-sclerosis/