The quantitative assessment of interstitial lung disease with positron emission tomography scanning in systemic sclerosis patients

Abstract

Objectives: The reversibility of interstitial lung disease (ILD) in SSc is difficult to assess by current diagnostic modalities and there is clinical need for imaging techniques that allow for treatment stratification and monitoring. 18F-Fluorodeoxyglucose (FDG) PET/CT scanning may be of interest for this purpose by detection of metabolic activity in lung tissue. This study aimed to investigate the potential role of 18F-FDG PET/CT scanning for the quantitative assessment of SSc-related active ILD.

Methods: 18F-FDG PET/CT scans and high resolution CT scans of eight SSc patients, including five with ILD, were analysed. For comparison, reference groups were included: eight SLE patients and four primary Sjögren's syndrome (pSS) patients, all without ILD. A total of 22 regions of interest were drawn in each patient at apical, medial and dorsobasal lung levels. 18F-FDG uptake was measured as mean standardized uptake value (SUVmean) in each region of interest. Subsequently, basal/apical (B/A) and medial/apical (M/A) ratios were calculated at patient level (B/A-p and M/A-p) and at tissue level (B/A-t and M/A-t).

Results: SUVmean values in dorsobasal ROIs and B/A-p ratios were increased in SSc with ILD compared with SSc without ILD (P = 0.04 and P = 0.07, respectively), SLE (P = 0.003 and P = 0.002, respectively) and pSS (P = 0.03 and P = 0.02, respectively). Increased uptake in the dorsobasal lungs and increased B/A-t ratios corresponded to both ground glass and reticulation on high resolution CT.

Conclusion: Semi-quantitative assessment of 18F-FDG PET/CT is able to distinguish ILD from non-affected lung tissue in SSc, suggesting that it may be used as a new biomarker for SSc-ILD disease activity.

Keywords: 18F-FDG PET/CT; Systemic sclerosis; interstitial lung disease; lung fibrosis; positron emission tomography.

Fig. 1

Visual examination of ¹⁸F-FDG-PET and HRCT Transverse and sagittal slides of ¹⁸F-FDG-PET scans and HRCT scans of a SSc patient without ILD (A) and a SSc patient with ILD (B). Increased ¹⁸F-FDG uptake in dorsobasal lung areas is marked by red arrows. FDG: fluorodeoxyglucose; HRCT: high resolution CT; ILD: interstitial lung disease.

Fig. 2

¹⁸F-FDG uptake in dorsobasal ROIs Each data point represents the mean of six dorsobasal SUVmean values of a patient. Mean values for the different groups were: SSc with ILD: 1.19; SSc without ILD: 0.60; SLE: 0.62; pSS: 0.74. SUVmean values were significantly higher in the SSc with ILD group compared with the SSc without ILD patients, SLE patients and pSS patients (P = 0.04, P = 0.003 and P = 0.03, respectively). Statistic test: Mann–Whitney U-test. FDG: fluorodeoxyglucose; ILD: interstitial lung disease; SUV: standardized uptake value; ROI: region of interest; SUVmean: mean SUV.

Fig. 3

B/A-p and B/A-t ratios (A) Mean values of B/A-p ratios were: SSc with ILD: 2.63; SSc without ILD: 1.65; SLE: 1.36; pSS: 1.42. The B/A-p ratio was higher in patients with ILD compared with patients without ILD, SLE patients and pSS patients (P = 0.07, P = 0.002 and P = 0.02, respectively). (B) Mean values of B/A-t ratios were: normal lung parenchyma: 1.45; ground glass: 2.95; reticulation: 2.79; reticulation with architectural distortion: 2.45. The B/A-t ratio was significantly higher in areas of ground glass and in areas of reticulation with architectural distortion compared with normal lung parenchyma (P = 0.02 and P = 0.02, respectively), but not in areas of reticulation without architectural distortion (P = 0.13). Statistic test: Mann-Whitney U-test. B/A-p ratio: basal/apical ratio at patient level; B/A-t ratio: basal/apical ratio at tissue level; ILD: interstitial lung disease; SUVmean: mean SUV.