[¹⁸F]FAPI PET/CT-based scoring systems for patient assessment in IgG4-related disease

Area of Science:

• Nuclear medicine imaging
• Radiopharmaceutical development
• Immunology

Background:

• ¹⁸F-Fibroblast activation protein inhibitor ([¹⁸F]FAPI) PET/CT is an emerging imaging modality for IgG4-related disease (IgG4-RD).
• Standardized quantitative analysis and image scoring remain challenges in IgG4-RD assessment.
• Accurate monitoring of disease activity is crucial for effective IgG4-RD management.

Purpose of the Study:

• To establish organ-specific reference thresholds for [¹⁸F]FAPI uptake in IgG4-RD.
• To develop and validate a novel, clinically applicable scoring system (FPAS-IgG4) for monitoring IgG4-RD activity.
• To assess the utility of [¹⁸F]FAPI PET/CT in differentiating active from inactive IgG4-RD.

Main Methods:

• Retrospective analysis of [¹⁸F]FAPI PET/CT scans from 85 IgG4-RD patients and 10 healthy controls.
• Definition of organ-specific uptake thresholds based on healthy individual data (mean + 3 SD).
• Development of the [¹⁸F]FAPI PET/CT Activity Score of IgG4-RD (FPAS-IgG4) using logistic regression and ROC analysis.

Main Results:

• [¹⁸F]FAPI PET/CT demonstrated high diagnostic performance (sensitivity 86.2%, specificity 83.3%) for IgG4-RD detection.
• The FPAS-IgG4 score was significantly higher in patients with active IgG4-RD compared to inactive disease (5.2±3.0 vs 1.7±1.3, p<0.0001).
• FPAS-IgG4 >2 achieved 93.2% sensitivity and 73.1% specificity for distinguishing active from inactive IgG4-RD, and was strongly associated with active disease (p=0.001).

Conclusions:

• [¹⁸F]FAPI PET/CT is a valuable tool for monitoring IgG4-RD activity.
• The novel FPAS-IgG4 scoring system aids in disease stratification and management.
• [¹⁸F]FAPI PET/CT facilitates objective assessment of IgG4-RD activity and treatment response.